Entrapment of Bradysia paupera (Diptera: Sciaridae) by Phaseolus vulgaris (Fabaceae) plant leaf

Abstract

Flies of the genus Bradysia (Diptera, Sciaridae) are considered as major insect pests of greenhouse-grown horticultural crops. The ability of hooked trichomes of the French bean Phaseolus vulgaris to impale and entrap herbivorous insects thus resulting in insect reduced longevity, reproduction and larval mortality is well known. The present study investigates under laboratory conditions the ability of hooked trichomes of bean leaves to entrap fungus gnats Bradysia paupera, in order to estimate the reduction of their population. We characterized the entrapment mechanism of hooked trichomes towards B. paupera using cryo-scanning electron microscopy, and evaluated the silicon distribution in hooked trichomes with the energy dispersive X-ray microanalysis. We evaluated the trapping efficiency of hooked trichomes in fertilized and unfertilized bean plants towards B. paupera, in comparison with insects feeding on the plant leaf such as black bean aphid Aphis fabae and young stages of the southern green stinkbug Nezara viridula. For B. paupera, we recorded about 30% of entrapped insects in unfertilized plants. Considering the number of entrapped insects in relation to the leaf surface, the percentage of entrapped insect was higher in unfertilized than in fertilized plants having lower density of hooked trichomes. The presence of P. vulgaris plants in greenhouses could represent a useful method in integrated pest management to reduce Bradysia spp. population.