Abstract

Soybean looper (Chrysodeixis includens) is an important defoliating pest, which has caused significant losses in Brazilian soybean crops. The present study evaluated the foliar consumption, feeding period and mortality of small (< 1.0 cm), medium (1.0 to 2.0 cm) and large (> 2.0 cm) C. includens larvae after infection by the virus Chrysodeixis includens nucleopolyhedrovirus (ChinNPV), isolate Chin-IA (I-A). The bioassay was performed in a completely randomized design organized in a 3 × 2 factorial combination (three size of larvae fed on soybean leaf discs, either treated or not with 4.0 × 10¹¹ PIB ha^-1 suspension of virus) with ten replicates per treatment. The average consumption of all three sizes C. includens larvae were significantly reduced after ingestion of soybean discs treated with virus, compared to the larvae from control treatment. The total consumption reduction was 95.6%, 69.4% and 45.9% for the small, medium and large larvae, respectively. Feeding period was significatively reduced for small and medium larvae infected by the virus, but not for large larvae. The corrected mortality level of soybean loopers ranged from 70 to 90% and was not significant different between the three larval sizes. The behavior and physiological alterations of larvae started on the third day, and the mortality occurred between fifth and sixth day after ingestion of infective particles of virus, therefore reducing their damage abilities. Based on the results obtained, ChinNPV can be considered as an important tool within integrate management to control C. includens, mainly when small larvae were predominant in soybean crops.

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