Variability in Plutella and its natural enemies: implications for biological control

Since 1996, as part of a cooperative ARS/CIRAD Plutella biocontrol program, 115 Plutella populations have been collected in 32 countries from cole crops and cruciferous weeds. Twenty-seven primary hymenopterous parasitoid species were found, especially Diadegma spp., Cotesia plutellae and Oomyzus sokolowskii. A number of fungal pathogens, isolates of Paecilomyces fumosoroseus, Paecilomyces sp., Metarhizium sp. and Beauveria sp. were found in Australia, Benin, Romania and Georgia respectively. Biological, biochemical and genetic differences have been shown in DBM and their natural enemy populations from different geographic origins. Marked differences have been found in the behaviour of C. plutellae and O. sokolowskii towards different populations of DBM and some inter population crossings resulted in failure or only male progeny. Metarhizium from Romania and Paecilomyces from Australia killed 70–95% of DBM larvae exposed to them; other pathogens were less effective. Biocontrol of DBM is required in the south western USA where another pest, Bemisia tabaci biotype B, present in the same habitat, is managed by biocontrol based means. For successful biocontrol of DBM it may be necessary to evaluate and select natural enemies based on their association with the target DBM population.