Utilising plant feeding phytoseiid predators for pest control: Pros and cons

While plant feeding is well documented in insect predators, in Acarine (=mite) biological control agents (ABAs) little is known. Our objectives in this manuscript were to: 1) review plant feeding in the predatory mite family Phytoseiidae and its effects on the plant; 2) evaluate the biocontrol efficacy of the phytoseiid plant feeder Euseius scutalis. Several studies on phytoseiids have demonstrated that species belonging to the genera Typhlodromus, Kampimodromus, Typhlodromalus, Euseius and Iphiseius compliment their diet by feeding from the plant. In contrast, other species belonging to the genera Neoseiulus and Amblyseius do not. Using scanning electron microscopy, penetration holes in the leaf epidermis of pepper plants were identified and were identical to the penetration holes in pollen grains fed on by E. scutalis. In potted pepper plant experiments in a growth chamber, plant weight and canopy size were negatively affected by very high E. scutalis populations. However, in pepper greenhouses, where predator levels were an order of a magnitude lower than our growth chamber study, effective control of the broad mite Polyphagotarsonemus latus was attained without any evident damage to the plant. Feeding on the plant can sustain the predator when prey is scarce thereby improving the sustainability of the system, providing the species is adapted to the crop. However such plant feeding predators may be more susceptible to both systemic and non-systemic pesticides and the mass production of these mites may need to be performed on a compatible plant host. To incorporate plant-feeding phytoseiids for pest control in organic horticultural crops, more studies are needed to determine plant-mite interactions, as these will be crucial for the sustainability of the system.