Location: Stored Product Insect Research Unit
Title: Horizontal Transfer of Methoprene by Tribolium castaneum (Herbst) and T. confusum Jacquelin du Val Authors
Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 2013
Publication Date: N/A
Interpretive Summary: In food facilities the majority of an insect population is typically within hidden locations that are difficult to reach with conventional insecticide application methods, but as insects move in and out of these hidden areas that they could pick up insecticide on their bodies and transport it back into these hidden areas. If this process results in transfer of insecticide from this individual to another and it causes negative effects on that individual then it is a process called horizontal transfer. This process is important in other pest systems, but has not been previously evaluated for stored-product insects in food facilities. In a series of laboratory experiments using red flour beetle and confused flour beetle, we showed that the insect growth regulator methoprene could be transferred from a treated to an untreated individual. When red flour beetle immature stages were exposed to a treated insect normal adult emergence was reduced. The confused flour beetle is susceptible to methoprene than the red flour beetle, so the effects of horizontal transfer were less apparent but adult emergence was still reduced. However, when immatures were able to survive exposure to methoprene treated individuals and emerge as normal adults, there reproductive ability was not affected. This is the first report indicating that methoprene can be transferred between stored-product insects and highlights a potential mechanism that might increase the effectiveness of insecticide treatments in reducing insect populations in food facilities such as mills, processing plants and warehouses.
Technical Abstract: In food facilities the majority of insect populations typically occur within hidden locations with limited direct exposure to insecticides, but there is potential for dispersing insects to transport insecticides into hidden areas and transfer insecticide to other individuals (i.e., horizontal transfer). In a series of laboratory experiments, the potential for transfer of the insect growth regulator methoprene between treated and untreated Tribolium castaneum (Herbst) and T. confusum (Jacquelin du Val) individuals was evaluated. In the first experiment, late-instar larvae were exposed to methoprene or water treated individuals in flour and their ability to develop successfully was determined. For T. castaneum, survival time for individuals exposed to methoprene treated individuals was shorter than those exposed to control individuals, but the difference was not significant for T. confusum. For both T. castaneum and T. confusum, the number of individuals that were able to successfully survive exposure and complete development without externally visible deformities was significantly reduced for individuals exposed to methoprene treated pupae or larvae relative to controls, but not when exposed to methoprene treated adults. In the second experiment, early-stage larvae, late-stage larvae, and pupae were similar in susceptibility to horizontal transfer of methoprene, even though they were exposed as immatures for different lengths of time. In a third experiment, the potential for sublethal effects due to horizontal transfer of methoprene was evaluated, but no difference in reproduction and oviposition was found for normally appearing adults that developed when exposed to methoprene treated or and control individuals. This is the first report indicating that methoprene can be transferred between stored-product insects and further research is needed to determine the impact this potentially has on pest populations.