Relocating Food

Urban cockroaches (B. germanica) search individually and independently for food. Items are not transported back to shelter, but eaten where they are found (Durier and Rivault, 2001a). In at least two cockroach groups the place where food is acquired differs from where it is utilized. Obtaining food and using it are thus separated in time and space, and the obtainer and the user are not necessarily the same individual (Zunino, 1991). Both groups that employ this "grocery store" strategy live in excavated underground chambers. The Australian soil-burrowing cockroaches forage during the night and the early morning hours of the wet season. After a rain and above a certain threshold temperature, they emerge, transport a quantity of dead leaves down into the burrow, and then do not emerge again until the next rain. Females grasp a food item in their mandibles and drag it backward down into the burrow. If they are approached when they are on the surface they will drop whatever they are carrying and "get a fair scuffle up" running back to their burrow (D. Rugg, pers. comm. to CAN). Gathered leaves are eaten by both the forager and any young offspring in the nest. Nymphs begin provisioning their own burrow when they are about half-grown. The food cache accumulated during the rains must sustain burrow inhabitants throughout the dry season (Rugg and Rose, 1991, pers. comm. to CAN). Other cockroaches known to transport and store food live in the tunnels of small vertebrates. Arenivaga apacha in the burrows of kangaroo rats in Arizona can be found nesting amid Yucca, Ephedra, Atriplex, and grass seeds that they have filched from the supply gathered and stored by the host rodent. "Our suspicion that the cockroaches gather and hoard provisions was confirmed when we saw the cockroaches carry dried dog food and sesame seeds that were sprinkled over the top of the aquaria soil into small caches underground" (Cohen and Cohen, 1976).

There are records of other cockroach species transporting food, but in these cases it occurs only in competitive situations. Rivault and Cloarec (1990) discovered that B. germanica began to "steal" food items from a dish as the items became small enough to carry and as food be came scarce. Adults and larger nymphs stole more food than younger nymphs, and more stealing occurred when two or more individuals were present at a food source than when a lone individual was feeding. Similarly, when LMR fed crowded laboratory cultures with rice, he observed young nymphs position individual pieces of it between their front legs and mouthparts and run off on their hind legs (identity of species is lost to memory).An-nandale (1910) documented Periplaneta americana using the mandibles to seize, hold, and transport termite alates in Calcutta.

Competition at food sources can trigger intraspecific aggression in B. germanica. The insects vary their tactics with age, and tailor them to the developmental stage of the opponent. Most agonistic interactions are between individuals of the same developmental stage.Young nymphs are primarily biters, but begin kicking more often as they develop; a good boot becomes more effective with the increased body weight characteristic of older stages (Rivault and Cloarec, 1992c). Young nymphs are generally tolerated by older stages and often reach food by crawling beneath larger conspecifics (Rivault and Cloarec, 1992a, 1992b). The relative amount of food required by large and small nymphs lowers the cost of benevolence for older insects.

Food relocation and aggression are both proximate mechanisms for obtaining and securing food from competitors. In burrow dwellers, relocation also allows them to feed at leisure in a location relatively safe from predators. Resource competition also may influence life history strategies, resulting in the distribution of competitors within a guild either in time (Fig. 3.5) or in space.

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