Ozone Toxicity and Walking Response of Populations of Sitophilus zeamais (Coleoptera: Curculionidae)

Ozone is a recognized alternative to the fumigants methyl bromide and phosphine for the control of stored product insects. However, as with fumigants in general, the potential sublethal effects of ozone on targeted insect species may compromise its efficacy and has yet to be investigated. Here, we determined ozone toxicity of 30 field-collected populations of the maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae), and assessed the walking response of adult insects from these populations to sublethal ozone exposure. Time-mortality toxicity to ozone at 50 ppm concentration in a continuous 2 liter/min flow indicated uniform susceptibility among the populations studied without any indication of ozone resistance (toxicity ratios [at LT50] > two-fold). In contrast, there was significant variation in walking activity among the maize weevil populations, which was not correlated with ozone susceptibility. This was not surprising because of the relatively uniform susceptibility to ozone among the maize weevil populations. Respiration rate affected ozone toxicity but not walking activity, whereas body mass was negatively correlated with walking activity but was not correlated with ozone toxicity. Based on our data, lower respiration rates may potentially lead to reduced ozone uptake whereas larger body mass limits walking activity. Ozone seems a promising alternative fumigant with low short-term risk of resistance development because of the high susceptibility and low variability of response to this compound. Furthermore, ozone reduces walking activity of S. zeamais that implies it likely reduces the chances of insects escaping exposure at the early stages of fumigation.