Potential of two insectivorous avian species and two insect predators for spreading Spodoptera littoralis nucleopolyhedrovirus (SlNPV) in Egyptian ecosystem

Abstract

AbstractThe polyhedral inclusion bodies (PIBs) of Spodoptera littoralis nucleopolyhedrosis virus (SlNPV) were extracted from droppings of both the house sparrow Passer domesticus Raf. and the cattle egret Bubulcus ibis Bon. Due to the wide host range of the SlNPV, the extracted PIBs were bioassayed versus newly hatched larvae (L1) of S. littoralis, S. exigua, Trichoplusia ni, and Autographa circumflexa belonging to the insect fauna of the Egyptian clover Trifolium alexandrinum L. and the greater wax moth Galleria mellonella. Mortality of treated neonates of the 5 tested insect species ranged between 80 and 100 % after 7 days from ingesting the PIB-contaminated diet. Feeding nymphs and adults of the earwig Labidura riparia Pallas on S. littoralis larvae infected with the nuclear polyhedrosis virus (SlNPV) passed viable PIBs in feces which were extracted and bioassayed versus lepidopteran larvae of L1. All of the virus-treated 5 lepidopteran species became infected with the virus and showed mortality of 44–96% at the 7th day post ingestion of the extracted PIBs. On the other hand, feces extract of the 3rd larval instar (L3) of the lacewing Parachrysopa pallens (R.) fed on the virus-diseased larvae of S. littoralis caused no mortality when assayed versus the 5 tested lepidopteran larvae proving absence of viable PIB polyhedra that might be due to the mode of larval feeding by external digestion of its host contents including the polyhedra. Results explain the potential role played by insectivorous birds in spreading the nucleopolyhedrosis viruses in the agroecosystem as well as certain predatory insects.