Field Studies on the Cumulative Response of Melittobia Sp. (Hawaiiensis Complex) (Eulophidae) to Varying Host Densities

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Abstract
Disused cells of Sceliphron assimile from 3 sites in S Jamaica were dissected and the percentage mortality from Melittobia sp. (M. hawaiiensis complex) with respect to density and to nest size calculated. The cumulative response of the parasitoid to varying host densities shows a density-dependent relationship which levels off at high densities, but additionally, a decline in the response at still higher densities is indicated. Explanations for the leveling off and possible fall of the response curve for the interaction between Sceliphron and Melittobia are considered. Mutual interference between searching Melittobia, the reproductive potential and density dependent mortality of the parasitoid and its sex-ratio do not satisfactorily explain the decline. Polymorphism and the production of migrants and the erratic searching behavior of the parasitoid may both contribute towards the decline of the response. Additionally, parasitization by Melittobia was less likely in the distal than in the basal cells of Sceliphron nests (P < 0.01), an effect which reduced percentage parasitization in larger nests. Since large nest size was correlated with high density (P < 0.01), this at least was a partial explanation of the decline of the response at high densities.

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