Pupation, adult emergence, and F1 egg hatch after irradiation of Spodoptera frugiperda (Lepidoptera: Noctuidae) last instars

Abstract

The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a quarantine pest that may be found as eggs or larvae on a number of fresh vegetable and fruit commodities. The objective of the research was to evaluate the effects of gamma radiation as a phytosanitary treatment applied to the 5th (last) instar larvae. Larvae were reared on an artificial diet. Each treatment of twenty 15–20 d-old larvae had 5 repetitions. The larvae were irradiated with doses of gamma radiation of 0 (non-irradiated control), 50, 100, 200 and 300 Gy in a Cobalt-60 source (Gammacell-220) at a dose rate of 508 Gy/h. Pupation, adult emergence and hatching of F1 eggs were monitored. When the last instars were irradiated with100 Gy the rates of pupation, adult emergence and F1 egg hatch were 85, 39 and 50 percent, respectively, and the corresponding values in the non-irradiated control were 95, 85 and 90 percent, respectively. However, when the last instars were irradiated with 200 Gy, the pupation rate was reduced to 30 percent and adult emergence was reduced to 10 percent, and all of the adults that emerged were deformed, unable to fly, and died after about 2 h. Therefore, irradiation with 200 Gy is recommended as the appropriate dose for phytosanitary irradiation of S. frugiperda eggs and larvae. In addition this study supports the previously proposed generic dose of 250 Gy for eggs and larvae of lepidopteran pest species generally.