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Oviposition Behaviour and Searching Efficiency in a Natural Population of a Braconid Parasitoid

1986; Wiley; Volume: 55; Issue: 1 Linguagem: Inglês

10.2307/4713

1365-2656

John N. Thompson,

Plant Parasitism and Resistance

(1) Searching behaviour in Agathis sp., an undescribed species of braconid wasp, was studied in the field during 3 years and compared with the oviposition behaviour of its host, Greya subalba (Lepidoptera, Incurvariidae). The larvae of G. subalba feed within the schizocarps (seed-pairs) of Lomatium dissectum (Umbelliferae), and Agathis females must search among the umbellets on each umbel to find the minority of schizocarps that contain larvae. (2) The number of schizocarps probed per umbellet by Agathis females closely fit a truncated geometric distribution, which is the distribution that also accurately fits the oviposition behaviour in G. subalba. This distribution, based upon the Shannon-Wiener information index, minimizes information on larval distribution to a searching parasitoid. The means of the distributions were also similar in the parasitoid and the moth. (3) There was no indication that Agathis females could determine and respond to larval distribution. Females did not probe more schizocarps on umbellets in which many rather than few schizocarps had larvae; they did not preferentially probe schizocarps with many rather than few larvae. Overall, females did no better than chance in finding larvae among the schizocarps they probed. (4) Females preferentially probed relatively large schizocarps within umbellets. Mass of probed seeds averaged 12.6% greater than the mass of schizocarps not probed. These larger schizocarps, however, did not have a higher probability of having G. subalba larvae than smaller schizocarps. (5) These data, the first to test similarity in distribution of movements of a parasitoid and its host, suggest that host movements that minimize information on larval distribution to a searching parasitoid may result in the adoption of a similar distribution of movements in the parasitoid and may indicate that the distribution of movements is an important focus of selection in the evolution of interactions. Nonetheless, it is not yet clear whether the pattern of movement in Agathis confers higher fitness than alternative patterns of movement.