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 s earching for prey patches and was characterized by long linear paths a nd 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 rea red on the aphid Acyrthosiphum pisum Ham's (Hem., Aphidae) crossed an artificial substratum previously contaminated by this prey, they chang ed their path direction and adopted intensive search. They probably pe rceived aphid odor tracks and consequently modified their walking patt ern. This gustatory capacity probably allowed very mobile larvae to lo cate prey patches more rapidly and improve encounter with preys in eve ry 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 extensiv e search. The weak response of these larvae to aphid tracks may have r esulted fi-om either a decrease in their sensitivity to gustatory aphi d stimuli or their difficulty in associating aphid odor with aphid pre sence. These larvae needed more time and more preliminary encounters t han larvae reared on aphids before catching prey.