Dose/Response of Codling Moth (Lepidoptera: Tortricidae) Eggs and Nondiapausing and Diapausing Larvae to Fumigation with Methyl Bromide

Abstract

Dose/responses of certain stages of the codling moth, Cydia pomonella (L.), to methyl bromide (MB) when fumigated at different temperatures (10, 20, or 30°C)and at normal atmospheric (NAP) or reduced (VAC) pressures were estimated. Stages and parameters tested were separated into two distinct groups. Stages in group 1 were less tolerant of MB; this group consisted of nondiapausing fifth in stars fumigated at 20 or 30°C and NAP and diapausing larvae fumigated at 20°C and VAG Stages in group 2 were more tolerant to MB. Group 2 consisted of 1- to 3-day-old eggs fumigated at 20°C and NAP, nondiapausing fifth instars fumigated at 10°Cand NAP, and diapausing larvae fumigated at 20°C and NAP. Lethal doses decreased at higher temperatures. For the same treatment and handling conditions, diapausing larvae (disturbed) were 2.3-fold more tolerant at LD50 or LD50 to MB than nondiapausing larvae. However, fumigation at a reduced pressure of 100 mm Hg significantly increased toxicity of MB. When VAC-fumigated, the response of diapausing larvae (disturbed) at LD50 or LD50 to MB was not significantly different compared with nondiapausing larvae fumigated at NAP. Handling diapausing larvae before fumigation significantly increased their susceptibility to MB, probably due to an increased rate of respiration as a result of the disturbance. Undisturbed diapausing larvae were 1.7-fold more tolerant at LD50 of MB than those disturbed due to handling within 1 day before treatment. At LD50, undisturbed diapausing larvae were 1.7-fold more tolerant than the stages in group 2 and 4.0-fold more tolerant than the stages in group 1.