© 2007 The Authors Journal compilation © 2007 The Royal Entomological Society Agricultural and Forest Entomology (2007), 9, 189–199 DOI:10.1111/j.1461-9563.2007.00335.x Introduction In the last few years, significant locust and grasshopper prob- lems have been reported in many parts of the world, includ- ing major outbreaks in Central Asia ( Latchininsky and Gapparov, 2000), parts of the U.S.A. (Lorentzen, 2002) and north Africa and the Sahel (Enserink, 2004; FAO, 2005). Biopesticides based on the mitosporic fungus, Metarhizium anisopliae var. acridum (= Metarhizium flavoviride Gams and Rozsypal; Driver et al., 2000), have shown considerable potential for biological control of locust and grasshoppers and have been tested extensively throughout Africa, Australia and parts of Europe and Latin America (Thomas et al., 2000; Lomer et al., 2001; Thomas and Kooyman, 2004). Indeed, 2005–06 saw operational use of M. anisopliae var. acridum Development of a model for evaluating the effects of environmental temperature and thermal behaviour on biological control of locusts and grasshoppers using pathogens Justine I. Klass, Simon Blanford and Matthew B. Thomas NERC Centre for Population Biology, Imperial College at Silwood Park, Ascot, Berks., SL5 7PY, U.K. Abstract 1 Recent years have seen an upsurge in locust and grasshopper populations in many parts of the world. Environmentally sustainable approaches to locust and grass- hopper control may be possible through the use of biopesticides based on ento- mopathogenic 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 applica- tions. 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 satis- factory to guide operational use of the biopesticide. 4 The model was subsequently used for a prospective evaluation of the perform- ance 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 con- trol operations, develop improved application strategies to optimize the perform- ance of the biopesticide and identify appropriate target species and environments. Keywords Body temperature model, Calliptamus italicus, Chortoicetes terminifera, Dociostaurus maroccanus, environmental temperature, Locustana pardalina, Metarhizium anisopliae var. acridum, Nomadacris septemfasciata, Oedaleus sen- egalensis, thermoregulation, Zonocerus variegatus. Correspondence:Matthew B. Thomas, CSIRO Entomology, GPO Box 1700, Canberra ACT 2601, Australia. Tel.: +61(02) 62464252; fax: +61(02) 62464362; e-mail: matthew.thomas@csiro.au