Abstract
Adults of Rhyzopertha dominica (F.), the lesser grain borer, Cryptolestes ferrugineus (Stephens), the rusty grain beetle, and Sitophilus oryzae (L.), the rice weevil, were exposed for 1, 24, and 72 h on wheat treated with concentrations of 0% (untreated controls) to 100% of the proposed label rate of an experimental formulation of deltamethrin + Methoprene + piperonyl butoxide synergist. Movement and velocity of movement were assessed after each exposure time using a camera-based monitoring system (Ethovision®). Movement of R. dominica decreased with increasing concentration and exposure time, so that movement had virtually ceased at the 48 and 72 h exposures. Cryptolestes ferrugineus was less susceptible compared to R. dominica, but there was still a general pattern of decreased movement and velocity of movement with increasing concentration and exposure time. Sitophilus oryzae was the least susceptible species, with less differences at the 1 h exposure interval compared to the other two species, but after 24–72 h, the patterns of declining movement and velocity were apparent as the concentration increased. Data were analyzed using curve-fit equations to show the relationship between concentration and exposure time for each species. Results show that the Ethovison system can be used to assess the sub-lethal effects of exposure to grain protectant insecticides and elucidate behavioral variation between different stored product insects.
Highlights
The use of the insect growth regulator (IGR) methoprene for direct application to stored grains, and as structural treatments in storage and processing facilities, has been reported in on-going projects for more than 20 years [1,2,3,4,5]
Historical data and recent research show that Sitophilus oryzae (L.), the rice weevil, is much more tolerant to pyrethroids used as contact insecticides on stored grains and on treated surfaces, compared to Rhyzopertha dominica (F.), the lesser grain borer [7,8]
The objectives of this study were to (1) develop an experimental methodology for using Ethovision® to examine the mobility of stored product beetles after exposure to an insecticide, and (2) to evaluate movement after exposure to an insecticide that is under development that includes deltamethrin, methoprene, along with the synergist, piperonyl butoxide
Summary
The use of the insect growth regulator (IGR) methoprene for direct application to stored grains, and as structural treatments in storage and processing facilities, has been reported in on-going projects for more than 20 years [1,2,3,4,5]. Methoprene and IGRs can be reliable alternatives to traditional neurotoxic insecticides including organophosphorous (OP) and pyrethroid compounds [3,6]. IGRs generally do not kill adult insects and must be combined with a contact toxicant to target adults. Historical data and recent research show that Sitophilus oryzae (L.), the rice weevil, is much more tolerant to pyrethroids used as contact insecticides on stored grains and on treated surfaces, compared to Rhyzopertha dominica (F.), the lesser grain borer [7,8]. Recent research shows that a combination of methoprene with the pyrethroid deltamethrin may still give enhanced control of S. Recent research shows that a combination of methoprene with the pyrethroid deltamethrin may still give enhanced control of S. oryzae [9].
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