Abstract
The 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.
Highlights
The repeated natural occurrence of nucleopolyhedrosis viruses in populations of agricultural and forest insect pests is a fact pointing to existing and circulation of the virus in the agroecosystem
Habitat description and field treatment Accidentally, during a visit to a large area planted with the Egyptian clover Trifolium alexandrinum L. at Al Badrashin village in Giza governorate in April 2019 to collect nymphs and adults of the earwig Labidura riparia Pallas for studies, the field was found highly infested with the cotton leafworm Spodoptera littoralis (Boisd.), S. exigua L., and few larvae of the semi-loopers Trichoplusia ni (Hübner) and Autographa circumflexa (L.)
It is worth to mention that the polyhedral inclusion bodies (PIBs) stock suspension extracted from droppings of the cattle egret B. ibis contained 8.25 × 1011 PIBs/ml and that of the house sparrow P. domesticus contained 6.5 × 109 PIBs/ml
Summary
The repeated natural occurrence of nucleopolyhedrosis viruses in populations of agricultural and forest insect pests is a fact pointing to existing and circulation of the virus in the agroecosystem. (Passeriformis: Passeridae) versus newly hatched larvae of the noctuid’s cotton leafworm Spodoptera littoralis (Boisd.), the beet worm S. exigua L., the semi-loopers Trichoplusia ni (Hübner) and Autographa circumflexa (L.), and the pyralid greater wax moth Galleria mellonella L. It is to prove the presence or absence of PIBs in feces of the predatory labidurid earwig Labidura riparia Pallas and the chrysopid lacewing Parachrysopa pallens (R.) when adults and nymphs of the 1st predator and larvae (L3) of the 2nd one fed experimentally on S. littoralis virus-infected larvae
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