Aggregation behavior and effects of larva population density on biological traits of Ophraella communa (Coleoptera: Chrysomelidae) in the biocontrol of Ambrosia artemisiifolia (Asterales: Asteraceae)

Aggregation behavior is common in insects, and plays a key role in population dynamics. Ophraella communa LeSage is an important biocontrol agent against common ragweed (Ambrosia artemisiifolia L.), yet its aggregation behavior and density-dependent responses remain poorly understood. This study examined aggregation and intersexual attraction in O. communa and evaluated the effects of larval densities on its development and reproduction using a 2-sex life table approach. Behavioral assays showed that both males and females were significantly attracted to conspecifics of either sex, with no difference in attractiveness between genders. Attraction responses were density-dependent, at low density (5 individuals), only males attracted females, whereas at high density (50 individuals), both sexes attracted conspecifics of both sexes. Life table analysis revealed that larval density significantly influenced the development and reproduction. At a density of 10 individuals per branch, larval and pre-adult stages shortened, adult longevity increased, and pupal and adult survival peaked. Fecundity was significantly higher at densities of 5 and 10, with the longest oviposition period at density 5. Life table parameters reached their maximum at density 10, while density 25 supported prolonged reproductive activity. Adult body weight, body length, and head width also varied with density. Males exhibited the highest body weight at a density of 10, while females showed the greatest body length and head width at the same density. This study enhances our understanding of the aggregation behavior and density-dependent population dynamics of O. communa, and provide basis for optimizing mass rearing to improve biological control of A. artemisiifolia.