Improving secondary pick up of insect fungal pathogen conidia by manipulating host behaviour

It is often assumed that efficient application of a mycoinsecticide involve s hitting the target pest insect directly with a lethal dose of conidia. Ho wever, secondary pick-up of conidia from surrounding vegetation may be a mo re important source of inoculum. We have investigated ways of increasing co nidia acquisition by enhancing host movement. The aphid alarm pheromone, E- beta -farnesene, significantly increased mortality among peach potato aphid s. Myzus persicae Sulzer, that were exposed for 24 h to discs of green pepp er leaf sprayed with conidia of Verticillium lecanii (Zimmerman) Viegas the n transferred to fresh untreated discs to allow disease development. A more practical approach to increasing conidia pick-up appears to be the use of sub-lethal doses of the chloronicotinyl insecticide imidacloprid. One perce nt of the recommended dose, applied systemically, dramatically increased ap hid movement; quantified by image analysis of videotaped aphid behaviour. T his resulted in greater mortality from mycosis in experiments where aphids were exposed to insecticide-treated leaf discs that had been sprayed with f ungal conidia. A comparison with results from an experiment where conidia w ere sprayed directly onto aphids which were feeding on insecticide-infused pepper discs established that synergy was due to an indirect effect of the insecticide, i.e. through increased movement, rather than a direct effect v iz. predisposition of insecticide-weakened insects to disease.