Foraging for patchily-distributed leaf-miners by the parasitoid,Dapsilarthra rufiventris (Hymenoptera: Braconidae). II. Stopping rule for host search

We studied the stopping rule which the female parasitoid,Dapsilarthra rufiventris, uses for deciding when to leave the leaflet on which she is searching for leaf-mining larvae,Phytomyza ranunculi. She is unlikely to employ some current stopping rules, such as fixed-number and fixed-time rules and others. The searching female appears to deposit a marking pheromone on the leaflet. We formulated a model for predicting the amount of pheromone accumulated on the leaflet. The model assumes that she will deposit the pheromone on the leaflet at a given rate (a) per unit time which is proportional to search speed, and will leave it when the amount of pheromone reaches the thresholdL. In this modelL denotes the amount of the search effort spent on the leaflet. The model was fitted fairly well to the data. A comparison of the observed results with the predictions of the model suggests thatL increases markedly at the first encounter with the mine and at a lower rate for the subsequent encounters. This appears to be a kind of area-concentrated search, that is, searching for hosts for a while in the immediate vicinity after finding one host, and would be adaptive in foraging forP. ranunculi larvae, which exhibit clumped distributions among leaflets in the field.