A comparison of color-, shape- and pattern-learning by the hymenopteran parasitoid Microplitis croceipes

Abstract

Visual learning by the larval parasitoid, Microplitis croceipes Cresson (Hymenoptera: Braconidae) was investigated in flight chamber studies. During conditioning, free-ranging parasitoids were given a choice between two visual alternatives, only one of which offered a host larva. By using alternatives that differed in either color, shape or pattern, parasitoids could be conditioned to distinguish host sites on the basis of each of these visual cues. Tests during which no reward was offered were conducted following six rewards (ovipositions) at one of the two alternative stimuli. The test results reveal that M. croceipes learned to distinguish between shapes more readily than between colors or patterns. This high rate of shape learning in this parasitoid is in strong contrast to the learning capacity of honey bees, which have been shown to learn color better than pattern and pattern better than shapes. It is argued that the difference in learning capacities between M. croceipes and the honey bee may reflect the different selection pressures imposed on these two species by their natural ecological needs. The high rate of shape learning in  M. croceipes may be adaptive in dealing with the homochromatic but multishaped environment in which parasitoids have to locate their herbivorous hosts.