Coprophagy Facilitates Horizontal Transmission of Bait Among Cockroaches (Dictyoptera: Blattellidae)

Abstract

Baits offer several advantages over other insecticide formulations in the control of populations of the German cockroach, Blattella germanica (L.). However, they may fail to target certain life stages that feed only sparingly. Recently we have demonstrated that 1st instars are signiÞcantly more vulnerable to insecticidal baits when adults are present. By preventing adults or nymphs from eating bait we now conclude that adults translocate insecticide bait to the shelter, thus facilitating a horizontal transfer of the insecticide to nymphs. By tracking bait movement with a tracer dye, we show that nymphs take up adult-delivered bait via coprophagy. An alternative hypothesis, that adults delivered novel food odors to nymphs thereby stimulating them to forage and eat bait, was experimentally rejected. Analysis of time-lapse video records showed that 1st instars foraged sparingly compared with 2nd instars and adults, indicating that direct ingestion of a remotely placed bait accounted for little, if any, mortality in 1st instars. The magnitude of coprophagy in 1st instars was related to the proximity of the food to their aggregation site; nymphs ate signiÞcantly more adult feces when food was far from the shelter. We conclude that aggregating 1st instars are relatively sedentary, and that they depend on conspeciÞc foragers to deliver widely dispersed food. Innovative baiting strategies should therefore maximize forager-mediated translocation and delivery of slowacting bait insecticides to inaccessible cockroach aggregations.

Diet quality affects bait performance in German cockroaches (Dictyoptera: Blattellidae)

“…A number of effective, non‐repellent active ingredients have been incorporated within baits . Modern bait formulations can kill cockroaches through direct ingestion (primary kill), as well as through the uptake of translocated AI (secondary kill), whereby cockroaches, primarily first‐instar cockroach nymphs, are adversely affected following ingestion of (coprophagy) or contact with excretions containing the toxicant . Secondary kill through coprophagy is especially effective with slow‐acting AIs, such as hydramethylnon …”

Effect of Horizontal Transfer of Barrier Insecticides to Control Argentine Ants (Hymenoptera: Formicidae)

“…The donor termites delivered active ingredient into their respective colonies through mutual grooming and propagated the spread of active ingredient by trophallaxis. Kopanic and Schal (1999) showed that sedentary Þrst and second instars of German cockroach, Blattella germanica L., received lethal doses of hydamethylnon by consuming adult excreta (coprophagy) at aggregation sites. The use of a slow-acting insecticide, such as hydramethylnon, was important because most of the active ingredient was excreted 12-h postconsumption.…”

Secondary Transmission of Toxic Baits in German Cockroach (Dictyoptera: Blattellidae)

“…None of these experiments separated the role of coprophagy and cannibalism from that of contact with traces deposited on dead bodies and feces. As intestinal transit takes longer than Þpronil to kill cockroaches (Kopanic and Schal 1999), dispersion of Þpro-nil by feces is then negligible. Contamination through feces is much more likely to occur when feces fall on traces already deposited in the environment.…”

“…Several factors are responsible for secondary transmission. Kopanic and Schal (1999) showed the action of coprophagy whose role is limited by intestinal transfer lasting at least 12 h. Gahlhoff et al (1999) demonstrated the role of cannibalism of dead contaminated cockroaches.…”