Functional response and progeny production of the Madeira mealybug parasitoid, Anagyrus sp nov nr. sinope: The effects of host and parasitoid densities

Anagyrus sp. nov. nr. sinope Noyes & Menezes is a gregarious koinobiont parasitoid of the Madeira mealybug, Phenacoccus madeirensis Green. In this study, we explored the influence of host and parasitoid densities on the functional response and progeny production of Anagyrus sp. nov. nr. sinope. In the first experiment, which was designed to detect the occurrence of mutual interference among foraging parasitoids, we exposed a constant number of mealybugs (N = 60) to varying numbers of parasitoids (P = 1, 2, 4, 8, and 20). Mutual interference among 20 parasitoids reduced the number of mealybugs parasitized and the number of progeny produced per parasitoid by 9 and 7 times, respectively, compared to 1 parasitoid. The interference constant (m) ( SE) was estimated at 0.62 +/- 0.03. The presence of conspecifics increased the proportion of males in the offspring population. In the second set of experiments, the parasitoids were released alone or in groups of 2 or 4 into patches containing one of six parasitoid/mealybug ratios (1:2, 1:55 1: 10, 1:20, 1:40, and 1:60). Anagyrus sp. nov. nr. sinope exhibited a type II functional response. The estimated maximum number of mealybugs parasitized (i.e., the asymptote of functional response) over a 24-h period was reduced from 10.4 +/- 0.6 when foraging alone to 8.1 +/- 0.4 and 5.1 +/- 0.2 when in groups of 2 and 4, respectively. The number of progeny reflected the effects of the parasitoid and host densities on the parasitism rate. The highest number of progeny was produced by the parasitoids foraging alone in patches containing the highest parasitoid/host ratio (1:60). The results of this study suggest that both the host and parasitoid densities have significant impact on the functional response and progeny production of Anagyrus sp. nov. nr. sinope. (c) 2006 Elsevier Inc. All rights reserved.