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

Visual learning by the larval parasitoid, Microplitis croceipes Cresson (Hy menoptera: Braconidae) was investigated in flight chamber studies. During c onditioning, free-ranging parasitoids were given a choice between two visua l alternatives, only one of which offered a host larva. By using alternativ es that differed in either color, shape or pattern, parasitoids could be co nditioned to distinguish host sites on the basis of each of these visual cu es. Tests during which no reward was offered were conducted following six r ewards (ovipositions) at one of the two alternative stimuli. The test resul ts reveal that M. croceipes learned to distinguish between shapes more read ily than between colors or patterns. This high rate of shape learning in th is parasitoid is in strong contrast to the learning capacity of honey bees, which have been shown to learn color better than pattern and pattern bette r than shapes. It is argued that the difference in learning capacities betw een M. croceipes and the honey bee may reflect the different selection pres sures imposed on these two species by their natural ecological needs. The h igh 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.