WHAT DO MEXICAN FRUIT FLIES LEARN WHEN THEY EXPERIENCE FRUIT?

Authors: Robacker, David; FRASER, IVICH - USDA-APHIS-PPQ

Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2005
Publication Date: 7/8/2005
Citation: Robacker, D.C., Fraser, I. 2005. What do Mexican fruit flies learn when they experience fruit? Journal of Insect Behavior. 18(4):529-542.

Interpretive Summary: The Mexican fruit fly can be found from the southern United States, through Mexico, and deep into Central America. It attacks citrus, mangoes, and many other fruits, damaging the fruit and making it unfit for export to many foreign makets unless costly disinfestation treatments are undertaken to rid the fruit of the larvae. Recently, we showed that female flies accept fruit for egg laying more readily if they have previously been exposed to that fruit. This means that the flies learn something about fruit when they lay eggs in it and use the information to help them find that type of fruit again. In this work, we set out to determine what female Mexican fruit flies learn about fruit. We found out that flies learn the odor of the fruit, but not its color or size. Previously, we had shown that this fly is not instinctively attracted to grapefruit, oranges, or even one of its native hosts from its ancestral home in the mountains of Mexico. It is now becoming apparent that this species probably encounters its first fruit just by its proximity in the fly's habitat, then learns how to find it again by its smell. It is hoped that learning how these flies find hosts will provide insights that will lead to development of new strategies to control populations of these damaging pests. For example, perhaps cleaning orchards of all leftover fruit after harvest could reduce future populations of flies in the area just because emerging flies will not easily find fruit and may migrate to non-cultivated fruits that they will learn to prefer instead of the commercial fruit in nearby orchards.

Technical Abstract: Mexican fruit flies learn fruit characteristics that enable them to distinguish familiar fruits from novel fruits. We investigated whether mature Mexican fruit flies learn fruit color, size or odor. Female flies did not learn fruit color or size after experience with host fruits, including oviposition. However, green fruit and fruit models were more attractive than yellow and red fruit and fruit models regardless of previous experience. Females with grapefruit experience were more attracted to fruit models with extract of either grapefruit peel or pulp, than to models without extract. Females with no experience with grapefruit were not attracted to models treated with grapefruit extract. These results indicate that females learned fruit odor during exposure to grapefruit.