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Biocontrol News and Information
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September 1999, Volume 20 No. 3
- General News
- Training News
- Internet Round-Up
- Announcements
- Biorational
- New Books
Biorational
Integrated pest management (IPM) involves the use of many techniques, including biological control, to provide effective control of crop pests with minimum harmful side-effects. Those techniques which are compatible with the use of biological control or have little impact on natural enemies have been described as `biorational'.
Coffee berry borer (Hypothenemus hampei) was first identified in coffee some 130 years ago, and is now its most serious pest in many of the major coffee-producing areas of the world, including Latin America and India. A few coffee-producing countries (Costa Rica, Cuba, Panama) are still free of the pest, and for them stringent quarantine precautions are important, for transportation of seeds containing borers has been the vehicle for its worldwide spread. Crop losses can be severe, with 50-100% of berries attacked if no control measures are applied, leading to up to 50% crop losses and poor quality coffee which can be difficult to market.
A number of natural enemies, insects and pathogens, has been recorded from the borer. Two bethylids, Cephalonomia stephanoderis and Prorops nasuta, were introduced to many Latin American countries from Africa, particularly in the 1980s and 1990s, and seemed to establish easily. In addition, Beauveria bassiana is an important natural control agent in very wet regions including Colombia. However, these agents have not by themselves been able to control the borer and farmers worldwide still rely mostly on chemicals or hand picking to control the pest. Hence there is a need to develop IPM strategies to control this difficult pest, especially in Colombia, where the borer has become the country's most serious pest problem.
In Colombia the borer is widespread in over 650,000 ha of coffee. This report* summarizes activities carried out for a bilateral project on coffee IPM for Colombia during 1993-98, funded by DFID (the UK Department for International Development) and Cenicafé (Federación Nacional de Cafeteros de Colombia). The project encompassed both research and training, and focused solely on the coffee berry borer and its control. Activities included farmer studies (socio-economic and anthropological), basic research, the introduction of a new natural enemy, sampling, modelling and IPM-related research.
Studies of farmer adoption of control methods for the borer revealed that nearly all have adopted some form of regular picking in order to keep the borer under control. However, efficiency of picking depends on the age of the tree and the height of the branch above the ground; older trees and lower branches tend to carry berries with a disproportionately high level of borer infestation and are a serious source of re-infestation. Field experiments looking at the impact of berry removal found that removal of lower non-productive branches can be achieved without risk of infecting the tree with Ceratocystus fimbriata. However, although this reduces incidence of borer, there appeared to be no associated cost advantage. Importantly, farmers do not collect the large numbers of berries that fall to the ground before during and after harvest. These are an important reservoir of borer infestations, but they proved particularly difficult to remove and available mechanical methods were unsuccessful.
The coffee farmers in this project (85% of whom farmed less than 3 ha) tended to have small families, whose members were generally not involved in routine work on the farm. Instead, farmers hired labour, which they perceived as expensive. Although they had received extension training, safety aspects of insecticide use were poorly understood, as were technical terms used in extension work. Case studies revealed that farmers tend to apply higher-than-recommended doses of insecticide, while few have adopted sampling to determine the optimum time to control the borer. Most had tried spraying Beauveria bassiana to control the pest, but less than 10% had continued to use it, while most (two-thirds) used chemicals sprays, an average of three times a year. A study of a young coffee plot, in which there were 22 flowerings in 17 months, revealed that borer attack following these flowering episodes was not uniform. Even detailed sampling was unable to relate field damage to damage on the harvested crop. This suggests that it would be effectively impossible to develop a simple sampling method for farmers to be able to predict crop losses.
Studies of the borer life cycle indicated that the reproductive rate depends on the age of the berry. Borer growth and survival were best on cherries infested when they were more than 180 days old (i.e. more than 180 days after flowering), while mortality was high and few borers survived to become adults in berries attacked at less than 120 days old. Borers could complete their life cycle before harvest in berries attacked at 120-180 days old, and up to three second generation adults emerge per infested berry before harvest. Some third of emerging borers manage to re-infest berries in the same plot. However, emergence of borers was found to be fastest and greatest where felled material was left in the field following stumping to promote re-growth, and this causes substantial re-infestation of surrounding plots. The recommendation that farmers leave `trap' trees in cleared fields would seem not to be effective.
Extensive field releases of C. stephanoderis indicated that the parasitoid could control borer populations over a period of a year, but cost projections from mass-rearing suggested that it could never be produced sufficiently cheaply to make commercial releases economically viable. The principal action of the parasitoid was found to be predatory, and parasitism rates remained stubbornly low (at less than 10%), even at release rates of 100 wasps per infested berry. Laboratory studies contributed the information that the parasitoid developed too slowly and required too many immature stages of the borer for it to be an efficient control agent.
The eulophid Phymastichus coffea was introduced into Colombia, and has been established in the field. A rearing technique was successfully developed for it, although it had previously been considered difficult to rear, and by early 1998 up to one million wasps per month were being produced. First field results suggest it is more promising than C. stephanoderis or P. nasuta, with up to 67% parasitism recorded.
Ironically, results with Beauveria bassiana proved to be disappointing, despite the widespread and highly visible naturally occurring infestations in the field. It was most effective on borers attacking young berries, but its action was slow compared to insecticides. Although mortality at very high spore concentrations could get to 80%, this took some 30 days to develop fully. Extensive formulation work failed to improve its efficacy and reliability in the field, and analysis of Cenicafé work suggests that it is currently uneconomic to use and should not be recommended until technical problems have been overcome.
Entomopathogenic nematodes were found to be able to penetrate and infect borers inside berries, and a new Steinernema sp. was discovered.
A computer model of the borer and its effects on coffee was developed, including control activities, harvesting, etc., based on data collected during this project, and suggestions for borer research and management in Colombia are discussed.
The report concludes that IPM of coffee berry borer in Colombia is potentially complex, but that on the basis of what has been learned it is possible to rule out a number of potential elements: the bethylid parasitoids previously introduced, B. bassiana, numerical sampling and trap trees all play only a minor role in helping to control the pest. In the short term, this leaves cultural controls, insecticides, possibly P. coffea and modelling as the blocks from which to build an IPM strategy, and it is suggested that the logical way to do this may be to move away from sampling-based farmer decisions to model-based extension advice. The importance of thinking strategically about coffee berry borer in the longer term is stressed. It is suggested that cultural control might be promoted in young coffee (up to two years old) before serious infestations develop and while the procedures are relatively easy to carry out. Further research and modelling of the role of P. coffea is proposed. Importance is also attached to enhancing the transfer of coffee berry borer control technology to farmers, and the differing needs of large- and small-scale growers are considered.
*Baker, P. (1999) The coffee berry borer in Colombia. Final report of the DFID-Cenicafé-CABI Bioscience IPM for coffee project (CNTR 93/1536A). Chinchiná, Colombia; DFID-Cenicafé, 144 pp.
Report obtainable from:
CABI Bioscience UK Centre (Ascot),
Silwood Park, Buckhurst Road,
Ascot SL5 7TA, UK.
Price US$10.00 to developing countries, US$ 25.00 to developed countries and
commercial companies.
Contact: Peter Baker, CABI Bioscience UK
Centre (Ascot), Silwood Park,
Buckhurst Road, Ascot SL5 7TA, UK
Email: p.baker@cabi.org
Fax: +44 1491 829123
Pheromone Pot-pourri1
The past decade has seen many refinements in the use of pheromones worldwide for detecting and monitoring pests and for control of pest populations. Pheromones are chemicals produced by insects that elicit strong behavioural reactions in the same species at minute amounts. They are usually produced by females to attract males of the same species for mating. Since the first insect pheromone product was registered for commercial use in 1991, considerable effort has been put into making the theoretical possibility of pheromone use in pest management an economic reality.
Recently, research into the effects of pest kairomones and plant semiochemicals on parasitoid behaviour has suggested new avenues to be explored. Pest kairomones, used for host location, may be used to monitor parasitoid activity and population size. There may also be a role for pest kairomones and plant semiochemicals in enhancing parasitoid activity and populations, but this work is still at an early stage.
Pheromones are used for monitoring pest populations to collect data for optimizing decision making. Probably the earliest example of an area-wide monitoring system was established by Clive Wall in the UK for pea moth, and this system is still in widespread use in Europe. Pheromone monitoring is now a cornerstone of pest management systems worldwide. Pheromone traps are used in most crop systems, and traps are available for all economically important species. For example, there are probably not many commercial fruit orchards in Europe and North America without a pheromone trap.
Unlike crop pests, many forest pests are cyclical, erupting into outbreaks at intervals of several years separated by long periods of vanishingly low densities. Effective monitoring is key to keeping tabs on such species. One well-established system has used pheromone traps for the last ten years deployed at more than 700 sites throughout North America to monitor the spruce budworm (Choristoneura fumiferana), which fluctuates on a long cycle of 35-40 years. Before the advent of pheromone traps, pre-outbreak population build-ups generally went undetected until trees became visibly defoliated. Now, the use of pheromone-based systems to monitor populations of defoliating forest pests and to optimize treatment timings is widespread.
The Douglas-fir tussock moth (Orgyia pseudotsuga) is a native defoliator of western North American forests. Outbreaks occur in British Columbia about every seven to 13 years, and these cause extensive tree mortality among the primary host, the interior Douglas fir, Pseudotsuga menziesii ssp. glauca: in 1993 over 25,000 ha were defoliated, and similar damage was only narrowly avoided in succeeding years. Since then the Canadian Forest Service, in cooperation with the British Columbia Ministry of Forests and the USDA Forest Service has developed a management strategy. Areas vulnerable to future attack are identified on the basis of forest types and biogeoclimatic zones of previously defoliated stands. Pheromone traps are used to monitor populations in these areas. If a threshold number of males is reached for three consecutive years, an outbreak is predicted as likely to occur in the next few years. Intensive sequential surveying for egg masses is then conducted to assess whether an outbreak is developing and the level of defoliation to be expected, and these predictions are confirmed by larval sampling.
When an outbreak and unacceptable levels of defoliation are judged to be imminent, control measures are implemented. A mating disruption method (mating disruption is dealt with in more detail below) has been used, the first successful use of this technique against a forest pest in Canada. Aerial or ground sprays, using standard equipment, of a synthetic sex pheromone enclosed in polyvinyl chloride beads of 250-400 m in diameter (from Consep Membranes, Bend, OR, USA) at doses of 18 g/ha resulted in 100% mating disruption. Aerial or ground sprays of a naturally occurring nucleopolyhedrovirus (NPV) have also been successful. The NPV builds up naturally during outbreaks, and eventually puts an end to them. But precise spray timing is crucial as the virus needs to be applied soon after egg hatch for its optimum spread through the population. The value of pheromone monitoring is that it allows widespread monitoring and gives valuable forewarning of annual population build up. The spray is triggered before defoliation is visible from the air, and the NPV starts to build up in the population earlier in the outbreak than it would naturally, and thus the severity of the infestation can be effectively limited. Combining these treatments could be synergistic, and logistical or biological drawbacks of either method may be offset by the other. NPV treatment could keep populations to a level where mating disruption is most effective, while adult moths developing from uninfected larvae would be subjected to mating disruption.
Information: Managing Douglas-fir tussock moth outbreaks. Victoria, B.C., Canada; Pacific Forestry Centre, Canadian Forest Service, Information Forestry, April 1999, p.3.
Contact: Rod Maides, Canadian Forest Service,
Pacific Forestry Centre,
506 West Burnside Road,
Victoria, B.C. V8Z 1M5, Canada
Email: rmaides@pfc.forestry.ca
Fax: +1 250 363 0775
Fewer Shot-holes
Pheromone monitoring is also used in a management programme for black army cutworm, Actebia fennica, developed by the Canadian Forestry Service in British Columbia. There is no effective control strategy for this pest, so the accent is on outbreak prevention. Pheromone monitoring is used to determine whether to plant seedlings or not.
The black army cutworm is widely distributed throughout the north temperate and subarctic regions of the world, and occurs throughout most of Canada and the northern USA. Caterpillars are polyphagous, and have been reported as pests of conifer seedlings and blueberries and occasionally forage crops in North America. First visual evidence of damage, resembling shot-holes in the vegetation, is often observed for the first time by planting crews, at which time it is difficult and costly to alter planting programmes. It is therefore crucial to identify vulnerable sites during the planning stage.
A natural or prescribed fire is the triggering mechanism for an outbreak - so fire-clearance of sites for planting is playing with fire in more ways than one. Moths fly throughout July-September, and congregate on sites burned earlier that spring or the previous autumn. The eggs they lay during the summer hatch after some two months and overwinter as early-instar larvae in the soil. In spring, caterpillars remain buried in the top layers of the soil by day, emerging to feed at night. They are therefore extremely difficult to locate by visual survey, but finding new infestations early is crucial. Larval feeding is usually complete within six weeks of spring emergence, and most damage is caused by these first-season outbreaks, with often little damage in subsequent years. Although infestations are generally fairly localized, entire blocks of trees are occasionally defoliated, and damage to seedlings can have long-term effects on growth.
With a sporadic occurrence of outbreaks combined with rapid onset of feeding damage, knowing where and when it is safe to plant is important, but appropriate management involving careful monitoring and planning can minimize the damage. The importance of pheromone monitoring in this system is that it can detect potentially damaging insect populations long before visual monitoring of pests or damage would be effective.
Contact: Tom Gray, Canadian Forest Service,
Pacific Forestry Centre,
506 West Burnside Road, Victoria,
B.C. V8Z 1M5, Canada
Email: tgray@pfc.forestry.ca
Fax: +1 250 363 0775
The Chemical Ecology Unit at Simon Fraser University in British Columbia has carried out basic research on the identification of bark and ambrosia beetle pheromones and their application in forest and industrial settings. The results from work by John Borden and John McLean have been developed commercially by Phero Tech Inc., and this includes bark and ambrosia beetle management programmes.
Aggregation pheromones are used to lure the insects to traps so populations can be sampled. This monitoring information is combined with other observations to improve control programmes through better targeting and timing: a threshold is established, and catches above this number indicate a control programme should be initiated. In some instances it has been possible to show a good correlation between trap catches and potential insect damage.
Generally, mass trapping using large numbers of traps is not an effective control strategy, and should be approached with caution. However, it is sometimes a useful tool in combination with other techniques. This is demonstrated by ambrosia beetle control in British Columbia, which has used mass trapping for the last 15 years. Ambrosia beetle populations in sawmills, log sorting areas and around log boom storage areas are surveyed with pheromone-baited traps, and areas of high risk are mass-trapped using funnel traps.
Bark beetle aggregation pheromones are used in a rather different, to concentrate beetle populations in an area about to be logged. Removal of the infested timber by clear cutting or selective logging removes brood-containing trees and reduces field populations, which continue to be monitored with pheromone-baited funnel traps.
Information: Phero Tech Inc., 7572 Progress
Way, Delta, B.C. V4G 1E9, Canada
Email: admin@pherotech.com
Fax +1 604 940 9433
Internet: http://www.pherotech.com/
The gypsy moth, Lymantria dispar, is one of North America's most devastating forest pests. The European strain was introduced to Massachusetts in the 1860s and was quickly recognised to be a serious problem. The first and ultimately unsuccessful attempt to eradicate it began in 1890. It feeds on the foliage of hundreds of species, and its most common hosts are oaks and aspen. During heavy infestations trees may be completely defoliated. Males are strong fliers, although the females are flightless, and its range has increased inexorably. Even so, it still occupies only about 25% of the total area predicted to be susceptible to infestation. Until now, control of its spread was effected by monitoring for isolated populations occurring beyond its contiguous range, and then attempting their eradication by a combination of methods including mating disruption, sterile-male release and biological pesticide treatments. However, it continues to spread, and an additional threat persists in western North America in the shape of the Asian strain of the species, whose female is winged.
The gypsy moth mating pheromone, disparlure, was identified and synthesized in 1970, and many attempts have been made since then to manage low-level populations by mating disruption. Insects use sex pheromones to communicate for mating. Pheromones elicit strong behavioural reactions at minute amounts, they are species-specific and non-toxic. By permeating the atmosphere with synthetic pheromones, olfactory communication and mate finding can be prevented. Mating disruption works best when applied on an area-wide basis, so forest pests are good candidates. The European gypsy moth possesses characteristics both suited and ill-suited to this technique. Its high fecundity, highly polygamous males and clumped/aggregated distribution of females are far from ideal, but its flightless females, poor mating success at low densities and limited dispersal of males and single generation per year are more compatible with mating disruption. The USDA Forest Service mating disruption programme for gypsy moth recommends that the technique should only be used to manage isolated or area-wide low-density populations of the European strain of the moth.
The programme illustrates well some of the problems encountered with pheromone-based management, including the importance of adequate dispenser systems. Numerous formulations containing disparlure were evaluated during the early years, including hollow plastic fibres, gelatin microcapsules, and plastic laminated flakes. Although these seemed fine in the laboratory, in the field deposition and penetration were uneven, disparlure was inefficiently released, and there were major problems with the available aircraft release systems. Initial results were inconsistent and discouraging. However, a plastic laminate flake formulation (Disrupt II from Hercon) was registered with the US Environmental Protection Agency (EPA), which is still in use today. Disrupt II releases disparlure at a constant but slow rate. This is operationally too low during the male flight period in the first year and the high dose needed to rectify this is expensive. More seriously, although progress has been made with release systems and overall performance has been considerably improved, application problems persist and equipment performs erratically. An open-pore polymeric flowable bead formulation diameter was developed (Decoy GM from AgriSense, Fresno, CA - now ThermoTrilogy) that could be applied using conventional boom and nozzle systems. Initial trials demonstrated that the beads (range 50-1000 m diameter, median 275 m) released the pheromone too erratically and too fast (on average, flakes release 30-40% of their pheromone by day 42 after release, beads 50% by day 20) and further work is needed on additives to optimize suspension and adhesion of the bead formulation. The fast release rate can be compensated for by double applications, but with a concomitant increase in costs. AgriSense has a petition to the EPA to register the bead formulation, and 3M Canada also has a microencapsulated formulation that is being evaluated for gypsy moth control.
The USDA Forest Service is also looking at the use of countrywide monitoring to improve containment of the spread of European gypsy moth. The national Slow the Spread (STS) Project began in 1999, following a pilot study which demonstrated that application of the latest survey and management practices could slow the rate of spread of the European gypsy moth by 60%. The project is being implemented across a 2000-km frontier from North Carolina through to Michigan. The project goal is to use novel IPM strategies in order to slow the moth's spread westwards into uninfested areas. The project is based on the use of pheromone traps for intensive monitoring of low moth populations in the transition zone between areas generally considered infested and those considered uninfested, coupled with timely control of growing isolated populations. When males are trapped for several years in the same location, this is evidence of a breeding population, and suppression with mating disruption and/or sprays of Bacillus thuringiensis (Bt) or a formulation of a naturally occurring nucleopolyhedrovirus (Gypchek) is implemented.
Contact: Richard Reardon,
Forest Health Technology Enterprise Team, 180 Canfield Street, Morgantown, WV 26505, USA
Email: Reardon_Richard/na_mo@fs.fed.us
Fax: +1 304 285 1505
The sex pheromone of codling moth (Cydia pomonella), codlemone, was identified some 20 years ago, and in the USA the first commercial dispenser became available in 1991. The technique sounds simple: dispensers tied to branches release artificial sex pheromone, which confuses male moths looking for mates. Males normally follow a plume of natural pheromone emanating from a female moth and fly upwind to find her, but these plumes are 'lost' in a fog of artificial sex pheromone. Codling moth is a key pest of apple and pear (pome) orchards, and because consumers are squeamish about biting into the occasional worm, stringent control is crucial to the pome industry. In the absence of control measures it can damage up to 50% of the crop and can make it impossible to store as infested apples start to rot.
Initially there was low and slow grower uptake of the mating disruption technology because of its perceived high cost/low efficiency. Studies in the Pacific Northwest showed that growers needed to reduce insecticide applications by four or more per season for pheromone use to be economically viable; spraying machinery and time were still needed for fertilizer and fungicide applications, and insecticides were necessary for some secondary pests. In addition, mating disruption proved less effective than insecticides under high codling moth pressure, and there were significant failures of control at the 'edges' of pheromone-baited areas. Costs were also elevated because of the expense of the pheromone and the absence of an efficient applicator. However, interest was maintained because of public and farmer concern over high insecticide use, the development of insecticide resistance and, more recently, the moves to ban some widely used insecticides.
This year, a five-year large-scale areawide IPM programme for the management of codling moth in the Pacific Northwest region of the USA (which began in 1995) entered its final phase. The aim of this programme had been to take management practices used on a limited scale by a few growers and apply them in contiguous orchards owned and managed by several growers. The programme has been coordinated by the US Department of Agriculture - Agricultural Research Service (USDA-ARS) Yakima Agricultural Research Laboratory in Washington State, together with Washington and Oregon State Universities and the University of California at Berkeley. The management system uses not only mating disruption, but also Bt sprays and ichneumonid parasitoid (Mastrus ridibundus and Liotryphon caudatus) and sterile male codling moth releases. The goal was to get all orchards in a large area to function as a complex sustainable ecosystem, a process which it was envisaged would need several years to attain.
It is difficult to draw any definite conclusions because codling moth pressure varies between years, but certainly some of the aims of this ambitious programme are coming to fruition. There has been a large increase in farmer uptake and enthusiasm, and good results are being achieved at low codling moth pressure. Three years into the project, some farmers were reporting that they had halved use of insecticides and were looking forward to eliminating them altogether. Codling moth numbers have declined every year since the large treated areas were set up. By the end of 1998 seasonal catches in some locations were reduced from 1000/trap six years ago to single figures, while there was almost no (less than 0.2%) codling moth infestation at harvest. Even where pressure is high, growers found that a combination of half-rates of pheromone dispensers and spraying was successful in bringing moth numbers down to reasonable levels.
The picture is not entirely rosy, as there have been persistent problems with leafrollers, and an increasing incidence of (stink) bug problems. However, orchards that have been sprayed with insecticides for decades are not the ideal places to work in. Many of the secondary pests now pose a problem probably because their natural enemies have been knocked out, and the pest populations have bounced back while the natural enemies take longer to build up again. It is also important to remember that codling moth is the key pest for the industry, and does serious damage, while many of the secondary pests cause lesser, often only cosmetic, damage. Codling moth cannot be controlled by other biological methods alone (the larvae bore into the fruit and are protected) while the secondary pests tend to be surface or leaf feeders, and are more susceptible to, for example, Bt sprays, parasites and predators, and may eventually be kept under comparatively good control by the naturally occurring arthropod fauna.
One final note, the rate of expansion of pheromone use has decreased this year, owing to poor returns to growers for their apples. A timely reminder that making ends meet is the bottom line for farmers.
Contact: Tim Smith,
Washington State University
Email: smithtj@wsu.edu
Internet: http://pwa.ars.usda.gov/yarl/areawide/areawide.html
Another, and spectacular, example of mating disruption success comes from South Africa. Stonefruit (peach, nectarine, plum and apricot) orchards cover some 20,000 ha, and the key pest, especially on canning peaches, is the Oriental fruit moth, Grapholita molesta. Introduced in the late 1980s, this species has four to six generations per year in South Africa, and spread rapidly through the stonefruit-growing areas. By 1991 and despite intensive chemical control measures involving up to 13 organophosphate treatments per season, it was causing shoot damage and crop losses in canning peach orchards of up to 80% in the worst-affected cases. In the face of the collapse of the industry as growers began to uproot susceptible orchards, a mating disruption programme was trialled. Isomate-M (Pacific Biocontrol) was deployed in a contiguous 1200 ha of peach and nectarine orchards in 1991-92. The success of the strategy was phenomenal. In the entire area, only 69 adults were trapped by the end of the season, there was only isolated shoot damage, and no infested fruit was recorded.
Key to the success of this project was the involvement of the fruit industry, research and extension back-up, support by the product distributor and participation by all growers. However, the cost of the programme far-outweighed the cost of an insecticide programme because the pheromone components had to be imported, and this was identified as the reason that mating disruption of Oriental fruit moth has not been widely used since.
Mating disruption of codling moth on pome fruit (a high-value export crop) is much more widely practised in South Africa. Resistance to both azinphos-methyl and pyrethroids was increasing and, by the early 1990s, 30% fruit damage was recorded in some orchards even after 12 sprays. A project began in 1992 to assess the efficacy of mating disruption using rope-style dispensers Isomate-C and Isomate-C Plus (Pacific Biocontrol) together with supplementary insecticide sprays. By 1996 insecticide applications had been reduced an average of 32% and fruit infestation limited to about 0.3%. This combination of improved codling moth control and reduced insecticide usage was particularly noteworthy given the development of insecticide resistance and the high reproductive potential of the pest in South Africa, and the situation has improved further since. In the past season some apple orchards which received no sprays had 0% fruit damage, even with dispensers reduced from 1000 to 500-800/ha.
Contact: Tom L. Blomefield, Fruit,
Vine & Wine Research Institute,
Private Bag X5013, Stellenbosch 7599 South Africa
Email: tom@infruit.agric.za
Fax: +27 21 809 3400
Also: IOBC-WPRS Working Group, Montpellier proceedings [see below].
The grape berry moth (GBM), Endopiza viteana, is the most important insect pest of grapes in eastern North America. Mating disruption has proven a highly effective for managing this pest. Decoy GBM (AgriSense, Fresno, CA), a polymer-matrix-gel pheromone dispenser, was registered for use in Canada in 1992. These dispensers were commercially available from 1992 to 1995 but were never used on more than 4% of the 5400 ha of commercial vineyards in Ontario. The low rate of adoption was due to the relatively greater cost of pheromone compared with insecticide treatment, and the labour required to apply the dispensers at the recommended rate of 1000/ha. It was also suggested that the marketing strategy was at fault. Promoting mating disruption purely on the grounds that it was environmentally friendly did not cut much ice with growers, and an approach that focused on the benefits of using it as part of a pro-active resistance management programme would have probably had more impact.
Sprayable pheromone is being developed for controlling the GBM. This will permit growers to apply pheromone with conventional pesticide application technology, and in some cases in combination with other vineyard pest control products.
Contact: Mitch Trimble, Southern Crop
Protection & Food Reseach Centre - Vineland Agriculture & Agri-Food Canada,
Vineland Station, Ontario,
L0R 2E0, Canada
Fax: +1 905 5624335
Email: trimbler@em.agr.ca
Also: IOBC-WPRS Working Group, Montpellier proceedings [see below].
On the Scent
The IOBC-WPRS (International Organization for Biological Control - West Palaearctic Regional Section) Working Group on the Use of Pheromones and Other Semiochemicals in Integrated Control is coordinated by Peter Witzgall at the Swedish University of Agricultural Sciences at Alnarp. The group has traditionally taken the role of liaising between basic research and practical application, and regularly runs workshops and symposia [see Announcements, this issue]. Their Internet site hosts Pheronet [see Internet Round-up, this issue], based on the book ` List of Sex Pheromones of Lepidoptera and Related Attractants' by Heinrich Arn, Miklós Tóth and Ernst Priesner.
Amongst a variety of useful publications are the proceedings of a meeting held in Montpellier, France in 1996 on technology transfer in mating disruption. Detection and monitoring with pheromones is covered, including programmes for spruce budworm and the European cornborer, Ostrinia nubilalis. There is a wealth of information on mating disruption programmes in orchards and vineyards (including some of the codling moth, Oriental fruit moth and grape berry moth examples described above). Research on insect behaviour in relation to mating disruption includes the role of antagonist chemicals. Mass trapping, attract-and-kill techniques and the integration of pheromone techniques with microbial control are also included. Other key areas dealt with are methodology (novel methods for release) and technological and commercial aspects. The proceedings are on the Working Group website at:
Internet: http://216.172.92.219/iobc/index.html
A printed version is available from:
Mireille Montes de Oca,
IOBC Permanent Secretariat,
Montpellier, France
Email: iobc@agropolis.fr
Fax: +33 4 67047599
Contact: Peter Witzgall,
SLU - Box 44,
230 53 Alnarp,
Sweden
Email: peter.witzgall@phero.net
Fax: +46 40 462166
The costs of both development of pheromones and their use have tended to confine this technology to high-value crops. Effectively, they are only used by smallholder farmers in cash crops such as cotton (for example, see `Making Use of the Good Bugs in Cotton', Training News, and `Organic Cotton', New Books, both this issue). In addition, mating disruption works best on larger areas and as a consequence is difficult to apply on areas farmed by smallholders unless they are willing to work collaboratively.
IPM programmes using pheromones to control pink bollworm (Pectinophora gossypiella) and Helicoverpa bollworms are in use in India and Pakistan, but the biggest area under pheromone treatment, some 40,000 ha, has been in Egypt. Until recently, the Egyptian cotton industry was regulated by the government, and they introduced a centrally managed programme of IPM with pheromone monitoring as a core element in 1980. Mating disruption is used particularly against pink bollworm, and this was so effective that the Ministry of Agriculture produced an illustrated pamphlet for farmers to explain the methods. Amongst products used is Frustrate-PBW (AgriSense-BCS, UK), formulated as small polymer strips incorporating the P. gossypiella sex pheromone and applied to young plants by placing them over the terminals at the first appearance of moths. In the growing organic sector, pheromone trapping is used to reduce cotton leaf worm (Spodoptera littoralis) populations, but pheromones have been less effective against a new pest, spiny bollworm (Earias insulana). Knowing how to use pheromone technology effectively is a common problem for farmers. Following the withdrawal of central control and support, the Egyptian German Cotton Sector Promotion Program is focusing on farmer learning groups, in which farmers are getting together with extensionists to discuss problems, improve observation in the field and learn how they can improve decision making.
Information: El-Araby, A; Merckens,
K (1999) Egypt. In: Myers, D.;
Stolton, S. (eds) Organic cotton.
From field to final product, pp. 164-175.
Egyptian German Cotton Sector Promotion Program, Project Management Office, Midan Nadi
El-Said, Dokki, Cairo, Egypt
Email: cspp@brainy1.ie.eg.com
Fax: +20 2 3365415
NRI (the Natural Resources Institute, UK) have investigated the potential of mating disruption to control yellow rice stemborer (Scirpophaga incertulas) in India, a project which aimed to improve the productivity and sustainability of smallholder-based high potential rice production systems. They have been able to demonstrate season-long control of the stemborers by using the natural ratio of artificially produced sex pheromone in a Selibate release system (AgriSense-BCS) in trials at three locations in Andhra Pradesh. Selibate was developed for the control of striped stemborer (Chilo suppressalis). In this project, it was formulated as strings which were tied to or forced into the split ends of attachment sticks, and these were placed on sticks or bamboo canes some 1 m high. Assessed by pheromone trap catches, it was found that pheromone-mediated communication in two of the trial areas was reduced at least 94% for up to three months after pheromone deployment, and rice damage was reduced 40-83% in comparison to damage in conventional farmers' practice plots.
The work done by NRI in India has clearly demonstrated the effectiveness of the mating disruption system. The main barriers to entry of this technology are its comparatively high costs, which are further compounded by import taxes in India and the natural resistance of farmers to a technology where it is very difficult to see visible evidence of the effect of the product (no dead insects). A survey of farmers revealed that 92-100% of the farmers applied insecticides once against stemborers (the number varying between areas) and 60% in one area treated their plots twice. Even so, this represented only some 5% of rice production costs, and it remains to be seen whether they will, or can, pay for the more expensive pheromone technology.
Information: NRI, Chatham, UK
Internet: http://vwww.netcom.net.uk/~n/nri/pcpp/r6739.htm
AgriSense-BCS Ltd.,
Treforest Industrial estate, Pontypridd,
Mid Glamorgan
CF37 5SU, UK
Email: enzoc@agrisense.demon.co.uk
Fax: +44 1443 841152
The messages coming from these initiatives are similar. If they are to play an effective role in pest management, pheromones need to be economically competitive with chemical treatments, application technology needs to be simplified (and ideally it should be possible to combine pheromone deployment with other treatment applications), field persistence has to be improved, together with efficacy at high pest densities.
A key player in the cost stakes has been Shin-Etsu (Japan), whose development of acetylene derivatives paved the way for relatively low-cost mass production, and they now produce a wide variety of pheromone products. Application technology has also advanced. Deployment of hand dispensers may be semi-automated with clip-on ties that can be attached by long-handled devices, so growers no longer have to climb each tree with a ladder to tie on dispensers by hand. However, even with rope-style dispensers it has been estimated that less than 20% of pheromone is released into the air, the remainder being lost to photodegradation, isomerization and polymerization.
Working with codling moth and other orchard pests at the University of California at Riverside, a team led by the late Professor Harry Shorey was developing a pheromone dispensing system based on remote control mechanical timers that periodically dispense puffs of product from aerosol cans (or `puffers'). Field trials conducted over a number of years in California demonstrated that these devices could be more widely spaced than conventional dispensers that operate by passive diffusion, and the pheromones within the cans are better protected from environmental and chemical degradation. The cans can be filled with selected amounts of a number of chemicals, and thus used to control more than one species (for example, codling moth and leafrollers). The timed release system means that the pheromone release rate remains constant over time and is also not affected by weather conditions, At the time of Professor Shorey's death in August 1998, this system was at the point of commercialization following several years of extended field trials in California.
Sprayable microencapsulated formulations are also a promising development, but as described for the gypsy moth programme above, they have the big drawback of fast release, and therefore low persistence, in the field. Sprayable products are now available for a number of crop pests (including pink bollworm) and tree fruit pests (including Oriental fruit moth).
The production process involves mixing the pheromone with a polymer and forming microcapsules with diameters for pheromone products of generally around 20 m (half the diameter of human hair). The pheromones diffuse through pores in the capsule wall, which also protects the pheromone from the effects of oxidation and ultra-violet light. However, the small capsules, with their high surface area:volume ratio, release all their pheromone too quickly; current lifetimes are around 2-4 weeks. An investment by 3M Canada and the Canadian Government will allow a team led by Harald Stover at McMaster University to conduct research on the structure of polymers, particularly those used in pheromone microencapsulation, and it is hoped that this will lead to effective pest control over a longer time period.
Natural pheromones contain a number of components, but synthetic (commercially available) pheromone blends used in pest control are usually much simpler. For example, mating disruption of codling moth still relies largely on a single compound, codlemone, identified in 1971. The difference between natural and synthetic products is suggested to be one reason for the failure of mating disruption, especially at high pest densities.
Deployment of artificial sex pheromone stimulates search flights of codling moths in the tree canopy. Visual cues and the female pheromone signal, containing behaviorally active components other than codlemone, guide the males to calling females at close range. The increased male flight activity observed under codlemone treatment will thus lead to matings, especially at high population densities. Vulnerable areas include orchard edges and treetops where the concentrations of synthetic pheromone are lowest.
An interdisciplinary programme of MISTRA, the Swedish Foundation for Strategic Environmental Research is conducting research on pheromones and kairomones. Its overall goal is to develop biological control methods for some important insect pests in Europe, including codling moth and other pests in pome fruit orchards, stored-product pests in mills and bakeries (flour moths, flour beetles), and aphids, and the use of antifeedants for protection of conifer seedlings against pine weevils. The objective of the codling moth project is to identify behavioural synergists and antagonists, and to see whether the activity of the main pheromone compound can be amplified by blending it with these compounds.
A group of scientists in Sweden, Italy and France, coordinated by Peter Witzgall of the Swedish University of Agricultural Sciences, has looked at the effectiveness of sex pheromone/antagonist blends for disrupting mating in codling moth. Antagonists are usually pheromone compounds from closely related species which play a role in reproductive isolation. They disrupt the ability of male moths to respond to sex pheromones and may be very potent repellents. They have been shown to be effective mating disruptants on their own, but are most efficient and give the best communication disruption when blended with sex pheromone.
Contact: Professor Jan Löfqvist,
The Swedish University of Agricultural Sciences, Box 44, S-230 53 Alnarp, Sweden
E-mail: Jan.Lofqvist@vsv.slu.se
Fax: +46 40 46 21 66
Also: IOBC-WPRS Working Group, Montpellier proceedings [see above].
Natural enemies use a variety of chemical cues to locate their hosts. Female aphid parasitoids, belonging to seven species so far investigated, are attracted to aphid sex pheromones, which are potential cues for host location. So is it possible to use these pheromones to manipulate aphid parasitoid populations in the field? Robert Glinwood and Wilf Powell at the Institute of Arable Crops Research (IACR), Rothamsted (funded through the MAFF-LINK scheme by the UK Ministry of Agriculture Fisheries and Food, the Horticultural Development Council, the Home-grown Cereals Authority and the Processors and Growers Research Organization) have looked at the potential for pheromones to improve early season control of pest aphid populations on cereal crops.
Parasitoids can play a vital role in the regulation of aphid populations, but only if they are active in the crop during the initial period of aphid population increase. Glinwood and Powell demonstrated that parasitoid behaviour can be manipulated in the field, and they suggest that this provides the opportunity to develop an aphid control strategy based on the use of aphid sex pheromones.
They showed that the major braconid parasitoids of cereal aphids are attracted to aphid sex pheromones and will attack aphids present around pheromone lures. For potted cereal plants artificially infested with Sitobion avenae and exposed in the field for three days, parasitization levels on plants baited with sex pheromone lures were significantly higher than on unbaited plants. Only asexual aphids (virginoparae), which do not produce sex pheromone, were present on the plants, yet these were attacked by the parasitoids, indicating that parasitoids attracted/arrested by the lure will attack aphid morphs other than the sexual females (oviparae) that naturally produce the pheromone. Parasitism was enhanced in aphids on plants 20 cm from the lure for the generalist aphid parasitoid Praon volucre, and up to 1 m away for the cereal aphid specialist Aphidius rhopalosiphi; parasitism rates on plants at greater (15 m) distances were apparently not affected by the lures. Since A. rhopalosiphi is usually the dominant parasitoid species attacking aphids in cereal crops, it could be an important target species for a parasitoid manipulation strategy.
Further work showed that parasitization levels were higher and increased earlier in pheromone-baited field plots of winter wheat than in unbaited plots, and Powell and Glinwood argued that this indicates that the aphid sex pheromones encouraged parasitoid activity during the initial period of aphid population increase, the stage at which parasitoids can have their greatest impact as control agents.
When arable crops are harvested, aphid parasitoids must disperse into other habitats to find alternative prey populations. In temperate regions, the parasitoids overwinter in these habitats, and spend time foraging there the next spring, before dispersing back into the cereal fields. The key to early-season enhancement, then, is to encourage parasitoids to make this move early. A strategy is being developed at Rothamsted to concentrate over-wintering parasitoids into vegetation strips along field margins (designed and managed to provide aphid hosts and winter shelter) by using aphid sex pheromones as lures to attract the parasitoids when they disperse from cereal fields at the end of the summer. This, it is hoped, should ensure a more rapid recolonization of the fields the following spring.
Contact: Wilf Powell, IACR-Rothamsted,
Harpenden, Herts. AL5 2JQ, UK
Email: wilf.powell@bbsrc.ac.uk
Fax: +44 1582 760981
In an analogous situation, research and trials in East Africa looked at whether cropping regimes may be able to exploit the different reactions of pests and parasitoids to plant semiochemicals [see BNI 18, 27N]. A team of scientists from IACR-Rothamsted in the UK, and ICIPE (the International Centre for Insect Physiology and Ecology, based in Kenya) and KARI (the Kenya Agricultural Research Institute) showed that while undamaged plants of some species, such as Sudan grass (Sorghum sudanensis) and Napier grass (Pennisetum purpureum), repelled stemborer pests (Busseola fusca and Chilo partellus), others repelled the pests but attracted their parasitoids. Intercropping maize with molasses grass (Melinis minutiflora) significantly decreased populations of stemborers in the maize crop and increased larval parasitism by Cotesia sesamiae. They further demonstrated that a volatile component produced by undamaged molasses grass attracted the parasitoid but repelled gravid C. partellus. They suggested that intact plants with the ability to release such compounds could be used in 'push-pull' crop protection strategies to entice pests out of the crop and natural enemies in.
There is also evidence that some plants produce distinct semiochemicals in response to damage by different pests, and that these plant emissions can transmit herbivore-specific information that is detectable by parasitoids. De Moraes and co-workers showed using chemical and behavioural assays that tobacco, cotton and maize plants produced different volatile blends of chemicals with different pests. They also found that in field trials the specialist braconid parasitoid Cardiochiles nigriceps exploited these differences to distinguish infestation by its host, Heliothis virescens, from that by Helicoverpa zea.
Jennifer Thaler has now shown that manipulating the biochemical pathways implicated in defence systems against herbivores increased parasitism of lepidopteran pests in tomatoes. She sprayed plants with jasmonic acid to induce the octadeconoid pathway, which contributes to plant resistance both by directly killing herbivores and by enhancing the action of natural enemies. Although parasitoid performance was shown to be reduced on hosts reared on induced plants compared with control plants, parasitism of Spodoptera exigua by Hyposoter exiguae on treated plants was increased two-fold in an agricultural field. Thaler found that the expression of the octadeconoid pathway was associated with an increased attractiveness and/or retention of parasitoids to the plants. She notes that the abundance of three guilds insects (leaf-, phloem-, and cell content-feeders) was reduced following treatment of the host plants with jasmonic acid, and suggests that elicitors of plant resistance could be investigated as tools in pest management.
Information: Khan, Z.R. et al. (1997)
Intercropping increases parasitism of pests. Nature 388, 631-632.
De Moraes, C.M.; Lewis, W.J.; Pare,
P.W.; Alborn, H.T.; Tumlinson,
J.H.; (1998) Herbivore-infested plants selectively attract parasitoids. Nature 393,
570-573.
Thaler, J.S. (1999) Jasmonate-inducible plant defences cause increased parasitism of
herbivores. Nature 399, 686-688.
Biocontrollers are beginning to exploit pest kairomones as a tool for sampling natural enemy populations. In New Zealand, Landcare Research are using pheromone traps for monitoring populations of Cydia succedana, a seed feeder introduced for control of gorse. They have also been using traps to monitor the presence or absence of the braconid parasitoid Ascogaster in orchards.
Information: Suckling, D.M.; Hill, R.L.; Gourlay, A.H.; Witzgall, P. (1999) Sex attractant-based monitoring of a biological control agent for gorse. Biocontrol Science and Technology 9, 99-104.
We have reported on research aimed at recruiting natural enemies as dispersal agents for pathogens in recent issues. The `contamination device' for Glossina pallidipes and Glossina longipennis described in by Nguya Maniania and David Nadel in `Tsetse's Lethal Path' [BNI 20(1), 7N-8N] used a trap baited with cow urine to lure tsetse flies into a trap that contaminates them with the entomopathogenic fungus Metarhizium anisopliae.
Judith Pell and Michael Furlong at IACR-Rothamsted have been developing `lure and infect' strategies for management of the diamondback moth, Plutella xylostella in collaboration with scientists in Asia and, more recently, Africa (DFID Project No. R6615). The entomopathogenic fungus Zoophthora radicans is a widespread and important member of the natural enemy complex attacking the diamondback moth. Epizootics, which contribute to the suppression of larval populations, are common but often occur too late in the season to retain crop damage below the economic threshold. By combining Z. radicans with synthetic female sex pheromone Pell and Furlong hypothesize that epizootics can be encouraged earlier when pest populations are small. Male moths are lured, in response to sex pheromone, into inoculum stations where they become contaminated with the fungus. On leaving the inoculum station they return to the crop disseminating infection amongst the susceptible population with the potential to establish early season epizootics. Simple and effective inoculum stations have been designed and evaluated in laboratory and field studies. Future work will include more extensive field testing in different geographic regions.
Contact: Judith Pell,
IACR-Rothamsted, Harpenden, Herts. AL5 2JQ, UK.
Email: Judith.Pell@bbsrc.ac.uk
Fax: +44 1582 760981
The key to the future of pheromones in pest management is threefold: efficacy of product, ease of deployment and effective use, and this will involve research, industry and farmers in equal measure. Research has the role of improving the efficacy of synthetic pheromones by identifying key behavioural compounds, and industry needs to take on the commercial development of these highly specific (and therefore in many cases small-market) products. Industry is taking the lead in improving ways of dispensing pheromones, sometimes developing ideas from researchers elsewhere. The final step is training for the end-users, the farmers and growers. Growers' associations are ideally placed but do not exist in all sectors and/or regions, and finding ways of providing users with technical back-up will be crucial to ensuring adoption of pheromone systems. Pheromone-based control is a more complex technology than chemical control, and growers will need clear instructions and strict guidelines to follow.
The use of pheromones to control insect pests is still in its early stages, although a number of outstanding successes have enhanced the profile of the technique and stimulated a high level of interest, especially against a background of disillusionment with chemical control. The enormous wealth and diversity of chemical communication within the animal kingdom may offer a lot for specifically designed pest control techniques. If the next decade experiences a similar varied use of pheromones to the past one, and advances in formulations and synthesis continue at the present rate, then great strides can be achieved in pest management and control of both forest and agricultural pests. It would be, to paraphrase Heinrich Arn, an elegant way of doing it.