Biological Control Of Locusts Research Articles

Development of a model for evaluating the effects of environmental temperature and thermal behaviour on biological control of locusts and grasshoppers using pathogens

Abstract1 Recent years have seen an upsurge in locust and grasshopper populations in many parts of the world. Environmentally sustainable approaches to locust and grasshopper control may be possible through the use of biopesticides based on entomopathogenic fungi. Unfortunately, the performance of these biopesticides is highly variable with environmental temperature and host thermoregulatory behaviour critically determining the pattern and extent of mortality after applications. Here, we present a temperature‐dependent model that enables us to predict the field performance of Metarhizium anisopliae var. acridum, the key fungal pathogen used in locust biopesticides.2 The model was constructed using mortality rate data generated across a range of temperatures in the laboratory and is driven by environmental temperature data linked through host body temperature models.3 Model predictions were validated against empirical field data obtained for five species, Locustana pardalina, Oedaleus senegalensis, Zonocerus variegatus, Nomadacris septemfasciata and Chortoicetes terminifera. Mortality predictions were accurate to a 2‐day error in every 10 days. This level of resolution is satisfactory to guide operational use of the biopesticide.4 The model was subsequently used for a prospective evaluation of the performance of M. anisopliae var. acridum against two additional pest species, Dociostaurus maroccanus and Calliptamus italicus in Spain. Results suggest that this pathogen would work reasonably well against these species as long as early instars are targeted.5 The model could provide a useful tool to assist in interpreting effectiveness of control operations, develop improved application strategies to optimize the performance of the biopesticide and identify appropriate target species and environments.

Advances in biological control of locusts and grasshoppers in Mexico

A project to develop a biological control strategy for locusts and grasshoppers is being conducted in Mexico. Major activities include: surveys of entomopathogenic fungi, laboratory screening of isolates, testing of methods for mass production, and formulation and field evaluation of virulent strains.The Centro Nacional de Referencia de Control Biológico (CNRCB) has, in its entomopathogen collection, 40 isolates of Metarhizium spp. obtained from the Central American locust (Schistocerca piceifrons piceifrons). The isolates MaaPL16, MaaPL25 and MaPL40 are among the most virulent.A comparative analysis on Random Amplified Polymorphic DNA patterns between two Mexican isolates of Metarhizium, MaPL40 and MaPL32, and an Australian isolate of Metarhizum anisopliae var. acridum (FI-985), showed that the Mexican isolates and the Australian isolate have similar DNA fingerprints, suggesting they may belong to the same variety.Field trials using oil formulations of the MaPL40 and MaPL32 isolates against hopper bands of S. piceifrons piceifrons, applied at a rate of 50g of conidia in oil, 1 l ha−1, provided >90% reduction in the hopper bands 10 d after treatment. Comparative studies between the Mexican and the Australian isolates were conducted over a range of temperatures: results are reported in detail.

Assessing the feasibility of biological control of locusts and grasshoppers in West Africa: Incorporating the farmers' perspective

A participatory rural appraisal inthree West African countries examined thepossibility for replacing chemical pesticidesto control locusts and grasshoppers with abiological control method based on anindigenous fungal pathogen. The fungus iscurrently being tested at different sites inthe Sahel and in the humid tropics of WestAfrica. Structured group interviews, individualdiscussions, and field visits, were used toobtain farmers' perceptions of locust andgrasshoppers as crop pests, their quantitativeestimation of crop losses, and theirwillingness to pay for locust control. Farmersas well as plant protection officers generallyperceived locusts and grasshoppers as importantpests that cause significant damage. Farmerswere aware of some of the risks of the use ofchemical pesticides, but not of the potentialalternatives. The use of the fungus in anoil-formulation and standard Ultra Low Volume(ULV) equipment was demonstrated, and theresults discussed with farmers. Theirimpressions of biological control werefavorable, and they expressed an interest inusing the technology. Farmers' expressedwillingness to pay for locust control is small,but not negligible. Locusts and grasshoppersare very visible pests and thus amenable topressure from farmers to local administrators,as well as by farmers' relatives in the city onthe national government. Therefore, politicalpressure for locust control is strong, althoughnational governments spend little on it,depending mostly on foreign donors. Donors areincreasingly worried about the environmentaleffect of the large amounts of chemicalpesticides used on locust control, and arepushing for more benign alternatives. Theresults of the present survey indicate thatthere may be a potential market for abiopesticide against grasshoppers and locustson cash crops in the humid areas. The potentialmarket in the Sahel depends on a reduction ofcosts or a subsidy of its price. This subsidycould be justified by the expected reduction inenvironmental and health costs when replacingchemical pesticides. Since donors are thecurrent purchasers of chemical pesticides forthe Sahel, they would also be expected to beinvolved in the purchase of the biologicalproduct.

Prospects for Biological Control of the Red Locust, Nomadacris septemfasciata (Serville) (Orthoptera: Acrididae)

Prospects for the biological control of locusts and grasshoppers have become much brighter during the last ten years thanks to a number of international research projects. This paper examines a number of options, including one that is ready for immediate implementation: the mycoinsecticide, Green Muscle®, based on the fungus Metarhizium anisopliae (flavoviride) var. acridum. It has been registered in South Africa and other African countries are likely to follow during 1999. Trial results on grasshoppers and several locust species have been very encouraging, and preliminary tests on red locusts show potential as well. Recent research on pheromones also points to some interesting possibilities, both when used alone and in combination with a mycoinsecticide. Finally, microsporidian protozoans and rhabditid nematodes show some promise for long-term suppression of red locust populations, but more research and development is needed to demonstrate their potential.

Infection of Schistocerca gregaria (Orthoptera: Acrididae) hoppers by Metarhizium flavoviride (Deuteromycotina: Hyphomycetes) conidia in an oil formulation applied under desert conditions

In the framework of the LUBILOSA programme (Lutte Biologique contre les Locustes et les Sauteriaux), a field trial was carried out on hopper bands of the desert locust, Schistocerca gregaria (Forskal) (Orthoptera: Acrididae), in south-central Mauritania. The objective of the trial was to show that conidia of the entomopathogenic funbws Metarhizill171 flavoviride Gams and Roszypal formulated in oil would be able to infect and kill hoppers under desert climatic conditions. LUBILOSA is a research programme on the biological control of locusts and grasshoppers carried out by the International Institute of Biological Control (IIBC), Ascot, UK, the International Institute of Tropical Agriculture

Biological control of locusts and grasshoppers using a fungal pathogen: the importance of secondary cycling

Persistent chemical pesticides can provide an effective means of control against locusts and grasshoppers due to prolonged activity of the spray residue. However, use of these pesticides is now prohibited, and non-persistent chemical alternatives are substantially less successful. Here we show why it is expected that biological pesticides based on the fungal pathogen Metarhizium flavoviride will be highly effective in the control of both locust and grasshopper. We demonstrate, using novel population dynamic models containing measured estimates of horizontal transmission coefficients, that secondary cycling of the pathogen after a single spray application provides a biological substitute for chemical persistence. This has significant consequences for the economics of biopesticide use in pest control. Furthermore, by identifying that secondary cycling acts in a density-dependent manner, this study also highlights fundamental differences between conventional pesticides and biopesticides and how they might be used.

Biological Control of Locusts and Grasshoppers. Edited by C. Prior and C.J. Lomer (Wallingford: CAB International, 1992). xii + 394 pp.

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