Cockroaches as Trojan Horses for Control of Cockroach Aggregations With Baits.

Gel bait formulations of insecticides have been shown to be highly effective in managing German cockroach (Blattella germanica L. [Blattodea: Ectobiidae]) populations. Three potential reasons for this are high palatability of baits, the use of slow-acting insecticides, and their horizontal transfer within aggregations, a phenomenon known as 'secondary mortality'. Our objective was to determine whether horizontal transfer can go beyond secondary, to tertiary and quaternary effects, and to compare various gel baits with different active ingredients. We fed adult females a bait and recorded their bait consumption, moribundity, and mortality. Groups of first instars were then exposed to the dead females and their feces, secondary mortality was quantified, and a new cohort of nymphs was then exposed to the feces and dead nymphs (for tertiary mortality); this process was repeated for quaternary mortality. This design did not distinguish among the major mechanisms of horizontal transfer of insecticides, namely coprophagy and contact with feces, exposure to regurgitated fluids, and cannibalism and necrophagy of nymphs. All the tested baits caused 100% mortality of the adult females that directly fed on the bait and high secondary mortality (average of >85%) within 48 hr. Baits containing either dinotefuran, emamectin benzoate, fipronil, or indoxacarb caused tertiary mortality (average of 15-70%), but only the fipronil and indoxacarb baits caused some quaternary mortality. The relative importance of secondary, tertiary, and quaternary transfer of the active ingredient remains to be determined in field populations of the German cockroach.

Role of Cuticular Hydrocarbons in German Cockroach (Blattodea: Ectobiidae) Aggregation Behavior.

Aggregation can be adaptive by providing protection from predators, facilitating thermoregulation, and expediting the location of food, shelter, and mates. German cockroaches Blattella germanica L. (Blattodea: Ectobiidae), are obligatory commensals in human-built structures, where they aggregate in crevices during the day. The source of the aggregation pheromone that drives this behavior and its chemical identity remain unclear. Cuticular hydrocarbons (CHCs) in feces have been proposed to serve as aggregation pheromone, but this function has not been investigated in relation to visual and tactile cues that mediate aggregation. Our objective was to delineate how CHCs in the feces and on the cockroach body operate in conditions that reflect the German cockroach's ecology-either applied to shelters, representing fecal deposition, or to previously extracted cockroaches, representing shelter co-habitation with other cockroaches. Cockroaches and feces-conditioned filter papers were extracted, CHCs were purified by flash chromatography, and two-choice behavior assays were performed with first instar nymphs. Our results confirmed that nymphs preferred to rest within feces-conditioned shelters. However, purified CHCs did not elicit more aggregation than solvent-treated control shelters. Nymphs significantly preferred to rest in shelters that contained a CHC-free dead female, but the addition of CHCs to the female did not enhance aggregation. Nymphs preferred to aggregate with the CHC-free female over CHC-treated shelters. Finally, a methanol extract of feces was highly effective at eliciting aggregation, contesting previous reports that fecal CHCs serve as aggregation pheromone. We assert that CHCs play a minor, if any, role in the aggregation behavior of German cockroaches.