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Title: Egg limitation and the functional response of the parasitoid Campoletis grioti (Hym:Ichneumonidae)


Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2007
Publication Date: 9/6/2007
Citation: Varone, L., Bruzzone, O., Logarzo, G. 2007. Egg limitation and the functional response of the parasitoid Campoletis grioti (Hym:Ichneumonidae). Biocontrol Science and Technology 17(9):pp 945-955

Interpretive Summary: Biological control is an alternative or complement to chemical control. An important requisite for the use of applied biological control is to know the natural enemies and biology of the pest, and the aspects related with the interaction between both. One type of interaction is the “functional response”, which evaluates the response of the natural enemy to increases in the pest density. The functional should be considered for biological control programs because it describes an essential attribute of any candidate: its ability to find and attack host pests. We propose that the traditional methodology does not consider physiological status variations that can affect the obtained response type and its associated parameters, because the functional response is determined using short periods of time of the parasitoid female life. Therefore, an experiment was designed enabling the parasitoid to be studied throughout its entire life. Campoletis grioti female parasitoids were used as a model and Spodoptera frugiperda larvae as hosts. We measured the functional response of C. grioti each day from emergence to death and we compared the functional response parameters obtained each day. We also estimated the functional response with the data previously modified that simulate lack of egg depletion. We found that the response type obtained did not change throughout the parasitoids´ lifetime, but differences were observed in the associated parameters that describe it. When we utilized the modified data neither the functional response nor the parameters changed. We proposed that egg availability was responsible for the changes.

Technical Abstract: The hypothesis that mature egg availability during a parasitoid’s lifetime affects the functional response, as well as parasitoids handling time and searching efficiency, was tested. Campoletis grioti Blanchard (Hym: Ichneumonidae) female parasitoids and Spodoptera frugiperda Smith (Lep: Noctuidae) host larvae were used as an example. Each female of C. grioti was confined with different host densities (6, 10, 30, 50, 80, 120 and 160 larvae/day) of first and second S. frugiperda instars until the female died. We found that C. grioti showed a type II functional response, with a reduction in the number of parasitized hosts in relation to female ageing. Handling time and searching efficiency increased over time. When we standardized the data simulating unlimited egg supply, the functional response, handling time and searching efficiency became constant throughout the parasitoid’s life. We discuss the relationship between egg availability and functional response and its associated parameters, and its consequence on biological control programs.