Abstract
Experiments were carried out to investigate the egg-laying behaviour of the maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) in uninfested and previously infested (termed conditioned here) maize grains. The number of offspring produced and preferred grain type of the weevil were examined under laboratory conditions, along with the effect of the presence of egg plugs on the oviposition site selection. The number of progeny produced was higher in conditioned maize. The highest and lowest number of adults emerged from conditioned and uninfested maize, respectively. S. zeamais individuals were significantly more attracted to conditioned grains compared to uninfested grains. S. zeamais females laid more eggs on host grains already bearing conspecific eggs (that is, conditioned) compared to clean grains (that is, uninfested). The number of eggs per grain showed a contagious distribution because females laid additional eggs on grains already infested with more than one egg. The results of this study indicate the possible role of the aggregation pheromone, intraspecific competition and egg marking in the observed egg-laying behaviour pattern of this pest species. Key words: Maize weevil, egg, aggregation pheromone, oviposition behaviour, host marker.
Highlights
In some stored agricultural products, adult female insect pests must select suitable grain on which to place their eggs because the larvae are not able to migrate to alternative grain sources
This study demonstrated that S. zeamais adults are able to differentiate between conditioned and uninfested maize during grain-host selection and egg-distribution on grain under laboratory conditions
More individuals emerged from conditioned maize because females laid more eggs on this grain type compared to uninfested maize
Summary
In some stored agricultural products, adult female insect pests must select suitable grain on which to place their eggs because the larvae are not able to migrate to alternative grain sources. Insect larvae that develop and feed on the grain kernels of stored agricultural products are subjected to unique evolutionary problems. Adult females are able to vary their fitness according to whether they (1) space eggs out and minimise competition between larvae, or (2) lay eggs at random and risk losses in both the quantity and quality of offspring (Giga and Smith, 1985). The critical question is whether females are able to detect eggs that are already present within the seeds of host products. For emerging larvae to receive an adequate food.
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