Exploitation and interference intraspecific larval competition in the dipteran leaf miner, Agromyza frontella (Rondani)

The effect of competition among similarly aged larvae of the alfalfa blotch leaf miner, Agromyza frontella (Rondani), was investigated in laboratory studies over a range of larval densities (1–10 larvae per leaflet) commonly found on alfalfa in Quebec. In these studies A. frontella larvae were found to be resource limited when developing in small leaflets and (or) with other larvae. Larval mortality owing to interference (cannibalism) during the first two larval instars, and exploitation (starvation) competition during the third and final instar, increased in a density-dependent manner. Prepupal and pupal mortality increased and pupal weight decreased as larval density increased. However, pupal developmental rates and adult sex ratios of survivors were not significantly affected by larval density. Interference competition during the first two larval instars reduced larval density and thus diminished the probability that third-instar larvae would be subjected to exploitation competition. These findings were confirmed under field conditions.