Enormous effort has been dedicated to localizing and characterizing the aggregation pheromone of pest cockroaches. The results, however, are still equivocal. Ledoux (1945) first proposed that aggregation in cockroaches was the result of mutual attraction of a chemical nature, and Ishii and Kuwahara (1967,1968) identified fecal material as the source of the cue. Riding the wave of pheromone research during the 1960s, these authors dubbed the fecal chemical "aggregation pheromone." They suggested that it originates in the rectal pad cells and that it is applied to fecal pellets as they are being excreted. Cuticular waxes apparently absorbed the fecal pheromone also, as ether washings of the abdomen had higher activity than ether washings of other parts of the body. More recent work has identified more than 150 volatile and contact chemicals from German cockroach fecal pellets (Fuchs et al., 1985, in Metzger, 1995; Sakuma and Fukami, 1990). The attractiveness of individual components depends not only on the type of extraction used, but also the biological assay used to test them (reviewed by Dambach et al., 1995), and the stock or population of B. germanica used as test subjects. Mixtures of fecal compounds are generally more effective than single components (Scherkenbeck et al., 1999). Cuticular wax may be attractive independent of any chemicals absorbed from excretory material. Rivault et al. (1998) found that cuticular hydrocarbons alone, from any part of the body, can elicit aggregation behavior.
Fecal chemicals seem to function initially as short-
Table 8.2. Aggregation of cockroach nymphs on filter paper conditioned with the feces of other cockroach species. Six to eight trials were performed with each combination using 20 nymphs per run. Plus-signs represent significant aggregation to conditioned paper as compared to controls. From Bell et al.(1972).
Species conditioning papers
After 20 min P. americana
After 12 hr P. americana Blatta orientalis Parc. pennsylvanica Eub. posticus Blab. discoidalis Byr. fumigata
range attractants (Ishii and Kuwahara, 1967; Bell et al., 1972; Roth and Cohen, 1973), then as arrestants (Burk and Bell, 1973). Nymphs halt their forward progress when they encounter a filter paper contaminated with feces; the response, however, is not strictly species specific (Bell et al., 1972; Roth and Cohen, 1973). Cockroaches prefer substrates contaminated by feces of their own species, but will aggregate on surfaces contaminated by distant relatives (Table 8.2). Periplaneta americana was attracted to paper contaminated by all species tested, and after 12 hr, Parcoblatta pennsylvanica was attracted to none, not even their own. Locomotor inhibition is enhanced by social interaction between assembled individuals; a nymph is more likely to stop on feces-contami-nated filter paper if one or more nymphs are already in residence. Young nymphs are most responsive to the chemical cues, adults are intermediate, and middle instars the least (Bret and Ross, 1985; Runstrom and Bennett, 1990). Experience matters; nymphs that hatch in an aggregation are more likely to aggregate (Dambach et al., 1995).
The evidence suggests that the fecal substances that elicit aggregation behavior in cockroaches, then, are not pheromones in the classic sense, but a functional category of behavior-eliciting chemicals (Brossut, 1975). Their origin is unclear, they are poorly defined, and they lack specificity. Pheromones are, however, clearly implicated in two species, Blab. craniifer and Eub. distanti, where the origin of the intraspecific attractant has been traced to the mandibular glands (Brossut et al., 1974; Brossut, 1979). In these cockroaches the pheromone is secreted by all individuals at all times except during the molting period. The insects are unattractive from 72 hr before to 24 hr after ecdysis (Brossut et al., 1974; Brossut, 1975). This inactive period occurs because the mandibular gland is lined with cuticle (Noirot and Quennedy, 1974), which is shed along with the rest of the exoskele-ton during molt.
Was this article helpful?