The effect of rearing the ladybird Harmonia axyridis on Ephestia kuehniella eggs on the response of its larvae to aphid tracks

Larvae of Harmonia axyridis Pallas (Col., Coccinellidae) exhibited two walking patterns during prey search. Extensive search occurred when searching for prey patches and was characterized by long linear paths and a fast speed. Intensive search, which appeared after the ingestion of a prey in a patch, resulted from a lowering of the linear speed and an increase in the number of stops and angular speed. When larvae reared on the aphid Acyrthosiphum pisum Harris (Hom., Aphidae) crossed an artificial substratum previously contaminated by this prey, they changed their path direction and adopted intensive search. They probably perceived aphid odor tracks and consequently modified their walking pattern. This gustatory capacity probably allowed very mobile larvae to locate prey patches more rapidly and improve encounter with preys in every patch. H. axyridis larvae reared on a substitute prey, the eggs of Ephestia kuehniella Zeller (Lep., Pyralidae), for more than a hundred generations, also changed their path orientation but retained extensive search. The weak response of these larvae to aphid tracks may have resulted from either a decrease in their sensitivity to gustatory aphid stimuli or their difficulty in associating aphid odor with aphid presence. These larvae needed more time and more preliminary encounters than larvae reared on aphids before catching prey.