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  • Title: Functional response of Gonatocerus ashmeadi and the "new association" parasitoid G. tuberculifemur attacking eggs of Homalodisca vitripennis.
    Author: Irvin N, Suarez-Espinoza J, Hoddle M.
    Journal: Environ Entomol; 2009 Dec; 38(6):1634-41. PubMed ID: 20021759.
    Abstract:
    The functional response of two egg parasitoids, Gonatocerus tuberculifemur (Ogloblin) and G. ashmeadi Girault (Hymenoptera: Mymaridae), to varying densities of Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) eggs was studied in the laboratory. G. tuberculifemur showed a type II functional response where parasitism increased at a decreasing rate as host egg density increased from 5 to 40, reaching an asymptote of an upper limit of 9.3 host eggs within the 1-h exposure period. The instantaneous attack rate and handling time as estimated by the random predator equation were 2.28/h and 0.10 h, respectively. In contrast, G. ashmeadi showed a type I functional response where the number of hosts attacked followed a constant linear increase regardless of host density to an upper limit of 11.5 host eggs within the 1-h exposure period. Female G. ashmeadi parasitized on average 4.3 and 3.5 more eggs per hour when presented with 10 and 20 H. vitripennis eggs, respectively, compared with G. tuberculifemur. When 5 or 40 H. vitripennis eggs were offered, there was no significant difference in parasitism rates between parasitoid species. Percentage of female offspring was significantly higher (5%) for G. ashmeadi compared with G. tuberculifemur. Under the experimental conditions used in these evaluations, results suggest that G. tuberculifemur is an inferior parasitoid to G. ashmeadi.
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