Phytosanitary Irradiation of Heliothis virescens and Helicoverpa zea (Lepidoptera: Noctuidae)

Guy Hallman
Phytosanitary irradiation is being increasingly used as a phytosanitary treatment to disinfest fresh commodities of invasive species. Optimum irradiation treatment doses for a number of invasive species groups, such as the family Noctuidae, are required. This research was designed to provide data for developing an optimum generic irradiation dose suitable against all eggs and larvae of the Noctuidae. Last instars (the most radiotolerant stage normally found on exported commodities) of 2 noctuid
more » ... ities) of 2 noctuid species were studied, i.e., Heliothis virescens (F.) and Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae). There was no significant difference in emergence of normal-looking adults from H. virescens last instars reared on either a natural or an artificial host, i.e., mature pods of Phaseolus vulgaris L. (Fabales: Fabaceae) or a meridic diet, respectively. Two laboratory colonies of H. virescens were studied, one appeared to be more radiotolerant than the other and it was used for large-scale confirmatory testing of a putative phytosanitary irradiation dose treatment. A total of 14,366 last instars were irradiated with 150 Gy (actual measured dose distribution was 145-166 Gy) with none emerging as normal-looking adults. A total of 2,197 last instar H. zea reared on meridic diet were irradiated with the same dose and no normal-looking adults emerged. This research indicates that a treatment dose of approximately 150 Gy is sufficient as a phytosanitary treatment for these 2 noctuid species and adds to the body of research evidence that a generic dose treatment of 250 Gy is adequate to control eggs and larvae of Lepidoptera that infest fresh commodities.