Performing Department
Entomology
Non Technical Summary
The German cockroach, Blattella germanica, is an important domiciliary pest because it vectors human and animal pathogens, produces potent human allergens, and in large aggregations it can damage food, other goods and electronic appliances. Until the mid-1980s dwellings infested with German cockroaches were primarily treated with baseboard applications of broad-spectrum liquid organophosphate, carbamate and pyrethroid insecticides. Solid and gel bait products, incorporating relatively slow-acting non-repellent insecticides (e.g. abamectin, fipronil, hydramethylnon, indoxacarb), have gained in popularity over the past 20 years and now are favored by pest management professionals (PMPs) for German cockroach control. In 1988, just six years after the launch of the first effective commercial cockroach bait, PMPs began noticing product failures. One apartment near Gainesville Florida was particularly noteworthy because changes in German cockroach numbers were actually measured. In 1985, following treatment with Maxforce bait cockroach numbers declined by 95%, however, just three years later with continual bait applications cockroach numbers increased by 40%. Similar reports of bait failures were being received across the US and beyond. What was particularly surprising was that cockroach numbers in many of these problem accounts were not increasing due to conventional resistance to the toxicant, hydramethylnon. Instead, cockroaches survived because they no longer consumed the bait because of an aversion to an ingredient used to stimulate cockroaches to feed, glucose. Thus, cockroaches that favored glucose were killed by consuming the toxic matrix while glucose-avoiders survived producing subsequent generations of bait/glucose avoiders. This change in cockroach populations is only possible because the glucose-aversion trait is heritable,it is genetically based and passed from parents to offspring, resulting in rapid increases in the frequency of this trait when cockroach populations are exposed to glucose-containing baits. This project will address several important areas of German cockroach behavioral resistance and bait aversion that are key to the development and implementation of effective control methods. First, we will determine the role of secondary kill on bait aversion development. We will also investigate how bait aversion develops under various selection pressures, including diet regime and insecticide exposure. We will continue to screen field populations of B. germanica for aversion to glucose and other sugars as well and resistance to insecticides in an effort to understand the interplay between bait aversion and insecticide resistance. We are also interested in how aversion to nutrients such as glucose is maintained in field populations in the absence of selection with toxic baits and will thus investigate development and reproduction in averse and non-averse cockroaches strains with defined diets in choice and non-choice assays where food is either abundant or limited. Finally, we will work with the pest control industry to evaluate and refine new technologies and formulations for efficacy in controlling German cockroaches.
Animal Health Component
(N/A)
Research Effort Categories
Basic
60%
Applied
40%
Developmental
(N/A)
Goals / Objectives
This project is designed to address basic questions concerning the importance of behavioral resistance and bait aversion in the German cockroach, and to elucidate the mechanisms underlying these traits. The information generated by this project will be useful in the development and evaluation of new control methods and in refining existing technologies. Ultimate Project Goal is To improve control methods for German cockroaches based on a sound understanding of phenotypic variation in B. germanica behavior, nutritional ecology, digestive physiology and, gustatory receptor function. The Principle Objectives are To develop a clearer understanding of how nutrition and insecticide pressure select for bait aversion and resistance. To determine the how bait secondary-kill attributes impact bait aversion development. To elucidate the mechanism of glucose, and other sugar aversions, by investigating the molecular changes in gustatory receptor organization on gustatory receptor neurons. To assess the scope of bait aversion in German cockroach field populations. To understand evolutionary origins of glucose aversion prior to German cockroach-human interactions To work with the pest control industry to evaluate and refine new technologies and formulations for efficacy in controlling German cockroaches.
Project Methods
We are currently conducting macronutrient choice and non-choice feeding assays and diet assimilation and growth studies with glucose-averse and non-glucose-averse cockroaches using the geometric framework multivariate approach. We are exposing field-collected B. germanica to single-sugar hydramethylnon baits and recording the distribution of averse and resistant phenotypes produced. We will determine whether glucose is excreted by non-glucose-averse (wild type) cockroaches fed a glucose-containing bait, determine the relative secondary-kill effects of current commercial bait active ingredients formulated within a glucose-containing matrix on glucose-averse and non-averse early instar German cockroach nymphs and determine how horizontal transfer of commercial baits affects the survival of early instar nymphs from a field-collected bait-averse strain of B. germanica We will 1) describe the differential expression profiles of gustatory transcripts between the wild type and glucose-averse strains, 2) reduce the number of candidate gustatory receptors through localization of transcripts in the GRNs using immunohistochemistry, confocal microscopy and image analysis and 3) employ behavioral and electrophysiological studies with gene-specific RNAi and heterologous expression systems. Expression of candidate cockroach GRs on GRNs of Drosophila and in Xenopus oocytes will reveal GRs that function in glucose, fructose, and deterrent reception. We will evaluate field collections of German cockroaches received from pest management professionals from problem accounts for bait aversion and insecticide resistance. Other Blattella species are omnivores and detrivores, feeding on living and dead plant material. Many plants produce glucose-linked plant secondary compounds, e.g. glucosinolates, glycosides, glucotannins that act as insect feeding deterrents. We hypothesize that glucose is a signaling molecule and that glucose aversion may have evolved in response to these plant-derived compounds. Thus perception of glucose as deterrent may be adaptive. We will develop dose response curves for various glucose-linked allelochemicals as well as related compounds lacking glucose for both glucose-averse and non-glucose averse B. germanica. We will also conduct food choice assays incorporating these compounds and measure consumption, survival, growth and fecundity. We will also assess the extent of glucose aversion in related Blattella species. We will work with industry to evaluate new technologies and formulations for efficacy against German cockroaches. We will conduct laboratory and field experiments as appropriate to carry out these tests. The specific procedures for each trial will be decided in consultation with industry representatives.