Onion maggot feeding and development on heterogeneous sections of the onion bulb

When given a choice of feeding sites in laboratory arenas, Delia antiqua (Meigen) larvae exhibited a 3: 1 bias for internal vs outer sections of onion bulbs and distributed themselves non-randomly among identical preferred onion sections. Larval clustering did not appear to be correlated with increased fitness in the laboratory; larval development was identical across the range of densities from 1 to 50 larvae per onion. Larvae feeding on preferred internal sections developed 14% faster, were 38% heavier upon pupation, and were two times more likely to survive to the adult stage than larvae feeding on outer sections. D. antiqua larval food preference was therefore positively correlated with increased fitness.