Functional response of Chelonus oculator (Hymenoptera: Braconidae) to temperature, and its consequences to parasitism

The parasitization behaviour of Chelonus oculator (F.), egg-larval parasitoid of noctuid lepidopteran species, has been studied under laboratory conditions, using Ephestia kuehniella Zeller as host, at four different temperature levels (10, 20, 30 and 40 +/- 1 C) and five densities of host eggs (50, 100, 150, 200 and 250). A significant effect of temperature and parasitism density was observed. At 10 degrees C, there was no parasitism, whilst at 40 degrees C it was very low; presenting adequate values at the two other temperatures (20 and 30 degrees C). With regard to these facts, the functional responses of this parasitoid species were adjusted and we noted that they display Holling type III. Estimating the handling times from the respective mathematical expressions, we obtained 10.944 and 15.250 min, at 20 and 30 degrees C, respectively. These values are considerably higher than the respective times obtained by direct observation, 0.597 and 0.560 min for these temperatures (this difference is due to the fact that in the first case, unlike the second one, the time used for the search of the host is also included). The results obtained from the parasitization behaviour of Ch. oculator are discussed, also considering it as a candidate biological control agent against Spdoptera exigua (Hubner), beet armyworm, with a view to its possible use in greenhouse crops in Spain.