We were concerned with the impact of gender on short-range dispersal by the whitefly parasitoid Eretmocerus eremicus (Hymenoptera: Aphelinidae) because of its importance as a biological control agent. Laboratory results indicated that unmated females sustained, on average, vertical climbs 3.4 times longer in duration than mated females. Males, in comparison, were poorer fliers whether mated or unmated. In the field, horizontal dispersal patterns were similar for both genders when considered independently (e.g. 41% of males and 39% of females were caught 3 m from release sites; 16% of males and 15% of females were caught at 10 m). 87% of the parasitoids recaptured were male, in spite of sex ratios being near parity upon release. A separation in their vertical distribution was also observed, with over 95% of the males within 10 m of the release site recaptured at canopy height while 40% of the females were trapped 0.25 m or more above the canopy. The difference in dispersal characteristics between males and females may be resource based. It is important for males to find mates and they may have done so inside release containers or nearby release sites. While females have a similar requirement, they must also find whitefly hosts to parasitize. Our plots were nearly devoid of potential whitefly hosts at the time of these experiments, a major patch requirement was not available to females and, consequently, most dispersed beyond 25 m. Since the two genders exhibited dissimilar dispersal characteristics, this supports the claim that insect dispersal, even by small species, is more than passive. It is hoped this information will be useful when describing movement by E. eremicus and other small insects. It should prove equally useful defining release techniques for parasitoids being used for biological control.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA