1. The chrysomelid beetle, Cephableia consanguinea (Hispinae), is a monophagous herbivore of ffeliconia imbricata (Zingiberales: Heliconiaceae) in wet lowland forests of eastern Costa Rica.2. Within the study area parasitism by eulophids and trichogrammatids (Hymenoptera: Chalcidoidea), the most common source of Cconsanguinea egg mortality, varied in intensity from 35% to 50% during 1974-77.3. Spatial relationships between the probability of parasitism and egg density per leaf were the net result of two opposing trends. The probability of at least one egg on an egg-bearing H.imbria?a leaf being encountered and parasitized (here termed a 'discovery' of that leaf by parasitoids) increased significantly as egg density per leaf increased, The conditional probability of parasitism for other eggs present, given an attack on one egg, decreased with increasing egg density.4. The net result was a decrease in the overall probability of parasitism as egg density per leaf increased. Host aggregation appears beneficial in reducing the intensity of parasitoid attacks. 5. Despite this inverse relationship between the overall probability of parasitism and egg density per leaf, a model based on the binomial distribution provides a good description of the spatial aspects of this host-parasitoid interaction.
Trichogramma pretiosum*** Riley (Hymenoptera: Trichogrammatidae), a generalist parasitoid of lepidopteran eggs, intensifies search in patches contaminated by a kairomone associated with Heliothis zea (Boddie) (Lepidoptera: Noctuidae) oviposition sites. In the laboratory the parasitoid will search any kairomone‐treated patch, abandoning standardized (10 cm diam) patches if no hosts are located within 60–180 sec. Total time and searching time on patches in which hosts are discovered are more highly correlated with the number of hosts attacked (Nha) per patch than with actual host density. The parasitoid's perception of host density per patch is often “incorrect” in this sense. Handling time (Th) and time “wasted” in re‐handling hosts parasitized earlier in the patch visit consume a large proportion of total patch time. Several hypotheses which have been suggested to explain patch time allocation by other parasitoids and predators appear inapplicable to T. pretiosum. The ratio of re‐encounters with parasitized hosts to the number of hosts attacked appears to affect the allocation of patch time by this species. The results of previous field experiments are compared to laboratory observations of searching behavior.
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