Efficacy of propylene oxide against eggs of four key California-based stored-product insect pests

As a result of regulatory phase out of methyl bromide, the California-based dried fruit and nut industries increasingly use sulfuryl fluoride (SF) where rapid disinfestations of stored-product insect pests are required. However, SF is a species specific ovicide and the eggs of several key California pests are not adequately controlled by this fumigant. This study was conducted in the context of overcoming ovicidal deficiencies of SF and postharvest fumigants in general. We evaluated efficacy of propylene oxide (PPO), a fumigant with great ovicidal efficacy, against eggs of four stored-product insect species, namely, Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), and Amyelois transitella (Walker) (Lepidoptera: Pyralidae). Tests were conducted at 25°C under reduced (100 mmHg) or normal atmospheric pressure (NAP). Mortality tests on all insect species resulted in LC₉₉ values ranging from 24.2-167.9 mg/liter at 100 mmHg and 3.8-19.9 mg/liter at NAP. Corresponding CT (concentration x time) products were 48.4-674.4 mg h/liter and 89.9-477.9 mg h/liter, at 100 mmHg and NAP, respectively.  Differences in susceptibility to PPO were found. In general, coleopteran eggs in our tests were more tolerant to PPO compared to lepidopteran eggs. At 100 mmHg, for the species tested, the tolerance of eggs in decreasing order was C. hemipterus > T. castaneum > P. interpunctella > A. transitella. These data provide information on doses of PPO required to kill eggs of the four species tested and represent a critical initial step in formulating a SF-PPO blend to meet disinfestation requirements.