Laboratory studies on parasitism of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) by two species of Trichogramma Westwood (Hymenoptera: Trichogrammatidae) in different grains, and evaluation of traps for their monitoring

The aim of the present study was to evaluate two species of egg parasitoids under laboratory conditions for biological control of the Indian meal moth Plodia interpunctella, an emerging stored product pest in bulk grain. Trichogramma evanescens proved to be a better candidate for biological control compared to T. cacoeciae as it accepted and parasitised a higher percentage of Indian meal moth eggs. Consequently the foraging of T. evanescens was studied in detail. Preferred oviposition sites on individual seeds by P. interpunctella are the germ region and the raphe. Moth eggs were parasitised at both regions. P. interpunctella eggs received higher parasitism at the germ region compared to the raphe. In stored grain and rice, P. interpunctella eggs can be found in the upper 8 cm of the bulk. Foraging parasitoids were shown to enter up to this depth into wheat, oats, and paella and Basmati rice. Wheat and oats were found most suitable for foraging, as larger numbers of T. evanescens were able to reach this depth as compared to the rice varieties. Among different traps, i.e. probe traps, cone traps and wiregauze tubes with adhesive cardboard, cone traps proved best for monitoring T. evanescens. These cone traps as well as the wiregauze tubes were used for the first time to monitor Trichogramma spp. in bulk grain. Cone traps recorded T. evanescens both when placed on the grain surface and in 5 cm depth within the grain irrespective of the release technique of Trichogramma, i.e. release from cardboard cards or sprinkling loose parasitised eggs. The potential for release of Trichogramma spp. within an integrated control strategy for the Indian meal moth in bulk stored grain and rice is discussed.