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According to the optimal oviposition theory, the larval success of insects depends on the oviposition site selection by females. Females are expected to choose a site with many resources and few competitors or predators to allow the best performance for their progeny, assuming that 'mother knows best.' However, this is not systematically observed. The Aphidoletes aphidimyza larvae are generalist aphid predators and females consequently lay their eggs near or inside aphid colonies. The goal of this study was to investigate the impact of intraspecific competition on oviposition behavior of A. aphidimyza females. First, we counted the number of eggs laid by a female on a leaf with 20 aphids, in the presence of 0, 2, 4, or 6 conspecific eggs or in the absence of eggs but in presence of 3 virgin females. The same experiment was also performed under choice condition with 2 oviposition sites. Our results show that the presence of low densities of conspecific eggs, or the presence of conspecific females, have no significant impact on the number of eggs laid by A. aphidimyza females. One of the hypotheses advanced to explain these results is the advantages of conspecifics presence. At low densities, the presence of eggs on an oviposition site can indicate the suitability of the site for the females. The conspecific presence can also insure a dilution effect against predator and increase the presence of potential mating partners for this monogenic species. [ABSTRACT FROM AUTHOR]

Gregarious locust and solitary locust display significant differences in behavior, physiology, and morphology in response to the changes in population density. Here, we show that two phases also differ significantly in volatile composition and their emission dynamics along with the development and sexes. The body odors of the gregarious and solitary nymphs are mainly consisted of aromatic compounds, such as benzaldehyde, guaiacol, phenol, anisole, veratrole, and aliphatic acids (C2 and C6). PAN and 4-vinylanisole are present in gregarious locust, but are absent in solitary locust. These two compounds were completely lost in gregarious nymphs during solitarization process, but were obtained by solitary nymphs during gregarization. The amounts of benzaldehyde, guaiacol, and phenol only unidirectionally decreased from solitary to crowded treatment (see pages 60-72). Picture provided by Jianing Wei. [ABSTRACT FROM AUTHOR]