Toxicological studies have shown that the cockroach Periplaneta americana is a classical model for studying the mode of action of commonly used insecticides. In a previous study, we demonstrated that thiamethoxam and clothianidin decreased locomotor activity and decreased the locomotor activity in an open-field-like apparatus. Here, we tested the effect of the neonicotinoid acetamiprid when applied orally, topically, or injected into the haemolymph. We found that acetamiprid decreased locomotor activity in the open-field-like apparatus. When treated with acetamiprid, a strong alteration in locomotor activity was observed 1 h, 24 h and 48 h after haemolymph and topical applications. Oral application of acetamiprid demonstrated that it impaired locomotor activity at 24 h and 48 h. A comparison of the present data with our previously published results showed that neonicotinoids were more active when injected into the haemolymph compared to oral and topical applications. These findings increased our understanding of the effect of neonicotinoid insecticides on insect locomotor activity, and demonstrated that the cyano-substituted neonicotinoid, acetamiprid, was able to alter cockroach locomotor activity.

An association of food sources with odors prominently guides foraging behavior in animals. To understand the interaction of olfactory memory and food preferences, we used glucose-averse (GA) German cockroaches. Multiple populations of cockroaches evolved a gustatory polymorphism where glucose is perceived as a deterrent and enables GA cockroaches to avoid eating glucose-containing toxic baits. Comparative behavioral analysis using an operant conditioning paradigm revealed that learning and memory guide foraging decisions. Cockroaches learned to associate specific food odors with fructose (phagostimulant, reward) within only a 1 hr conditioning session, and with caffeine (deterrent, punishment) after only three 1 hr conditioning sessions. Glucose acted as reward in wild type (WT) cockroaches, but GA cockroaches learned to avoid an innately attractive odor that was associated with glucose. Olfactory memory was retained for at least 3 days after three 1 hr conditioning sessions. Our results reveal that specific tastants can serve as potent reward or punishment in olfactory associative learning, which reinforces gustatory food preferences. Olfactory learning therefore reinforces behavioral resistance of GA cockroaches to sugar-containing toxic baits. Cockroaches may also generalize their olfactory learning to baits that contain the same or similar attractive odors even if they do not contain glucose.

Contact toxicity against Periplaneta americana has never been tested with S. collinsiae root extract. Hexane, dichloromethane, ethanol and water extracts were tested in final-instar nymphs and adult P. americana by topical application method. The dichloromethane extract showed the high-est potency of contact toxicity against the final-instar nymphs (41-100% corrected mortality at 48 hours), lowest LC50 (1.5±0.2 %w/v at 48 hours), and lowest LT50 (36.1±0.8 hours at 10%w/v) while the water crude extract lacked the contact toxicity (0-0% corrected mortality at 48 hours). Signs of toxicity, such as excited movement, trembling body, motionlessness, and swollen abdomen segment including irregularly extended foregut were found at the both stages of P. americana dropping with solutions of dichloromethane extract. Detection of didehydrostemofoline distri-bution using IMS revealed that didehydrostemofoline distributed in the tissue of the dead fi-nal-instar nymph and adult P. americana contacting with dichloromethane extract, but it was not found in tissue of euthanized P. americana which exposed to the water extract. Didehydrostemo-foline in the extract was a cause of toxicity signs and death of P. americana via a contact route. Thus, dichloromethane extract and didehydrostemofoline could be used as an active ingredient and chemical marker in aerosol and spray formulations for cockroach control.

Saliva has diverse functions in feeding behavior of animals. However, the impact of salivary digestion of food on insect gustatory information processing is poorly documented. Glucose-aversion (GA) in the German cockroach, Blattella germanica, is a highly adaptive heritable behavioral resistance trait that protects the cockroach from ingesting glucose-containing-insecticide-baits. In this study, we confirmed that GA cockroaches rejected glucose, but they accepted oligosaccharides. However, whereas wild-type cockroaches that accepted glucose also satiated on oligosaccharides, GA cockroaches ceased ingesting the oligosaccharides within seconds, resulting in significantly lower consumption. We hypothesized that saliva might hydrolyze oligosaccharides, releasing glucose and terminating feeding. By mixing artificially collected cockroach saliva with various oligosaccharides, we demonstrated oligosaccharide-aversion in GA cockroaches. Acarbose, an alpha-glucosidase inhibitor, prevented the accumulation of glucose and rescued the phagostimulatory response and ingestion of oligosaccharides. Our results indicate that pre-oral and oral hydrolysis of oligosaccharides by salivary alpha-glucosidases released glucose, which was then processed by the gustatory system of GA cockroaches as a deterrent and caused the rejection of food. We suggest that the genetic mechanism of glucose-aversion support an extended aversion phenotype that includes glucose-containing oligosaccharides. Salivary digestion protects the cockroach from ingesting toxic chemicals and thus could support the rapid evolution of behavioral and physiological resistance in cockroach populations.

Our study examines the association of the presence of mildew, cockroaches, and pets in homes as well as household dust allergens with the prevalence and/or severity of allergic diseases. No study has concurrently assessed home environment exposures in relation to allergic conditions in the general US population. Data from 5,409 participants from the 2005-2006 National Health and Nutrition Examination Survey living in their current homes for ≥1 year were analyzed. Multivariate logistic regression analyses between home exposures and allergic diseases prevalence and severity were performed. In adjusted analyses, mildew was associated with higher current asthma, allergies, and allergic rhinitis prevalence; endotoxin, with higher current asthma prevalence), and dust Canis familiaris (Can f) 1, with higher allergic rhinitis prevalence. However, presence of cockroaches and dust Dermatogoides farinae (Der f) 1 were associated respectively with lower current asthma and allergies prevalence. Presence of mildew, dust Der f1, Dermatogoides pteronyssinus (Der p) 1, Feline domesticus (Fel d) 1, and endotoxin were all associated with asthma and/or wheeze severity. Non-atopic asthma was more frequent with mildew and/or musty smell dust and higher dust Fel d1 concentration, while atopic asthma was more prevalent with higher Can f1and endotoxin concentrations in dust. This study confirms previous relationships and reports novel associations, generating hypotheses for future research.