Factors Affecting the Postrelease Dispersal of Anaphes flavipes (Hymenoptera: Mymaridae), with Notes on its Postrelease Development, Efficiency, and Emergence1,2

Abstract

The dispersals of Anaphes flavipes (Foerster), an egg parasite of the cereal leaf beetle, Oulema melanopus (L.), possessed characteristic patterns and areas. As the number of females released increased, so did the dispersal area, but as the density of the hosts increased, the dispersal area decreased. In a single-factor analysis, host density accounted for nearly 67% of the observed variation for 14 releases, and a mathematical model is presented which includes a combined analysis of the effects of host and crop density and number of females released on dispersal area. A detailed analysis of 15 releases of A. flavipes indicated that predominant wind conditions during the first 2- or 3-day postrelease period were the major factors in determining the postrelease pattern, although temperatures of 16°C and below tended to delay and negate such influences. The direction of skewness corresponded with the direction of the prevailing winds, and the degree of skewness with the velocity of these winds. The number of eggs parasitized per parasite released varied from about 1 egg for every 2 females to nearly 5 eggs per female, and the number of eggs parasitized per released female tended to increase as the density of the hosts increased. The impact of predation on these results was demonstrated by the application of carbaryl at 2 additional release sites, where the number of eggs parasitized per parasite was estimated to be 6.6 and 15.3. The number of days required for the development of A. flavipes under field conditions in 1966 and 1967 ranged from a minimum of 9–10 days at an average hourly developmental temperature of about 21.5°C to a maximum of 30 days at an average hourly developmental temperature of 13°C. The evidence provided from these results indicates that the number of generations per year which can easily be detected on ova of O. melanopus in northern Indiana is 2 (although as many as 4 may develop), and for 2 generations per year to be the case, the F1 generation must develop in the first ova laid on winter wheat if there is to be parental material for an F2 generation to develop in the ova laid on oats. Under field conditions, males tended to emerge before females, and emergence for both sexes was usually confined to early morning (0300–0600 hours).