Journal of Insect Science (2003) 3 (33), p. 24 (Tamo et al.)

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Cristina Tamò, Liselore Roelfstra, Guillaume Suzanne and Ted C.J. Turlings (2003)
Odour-mediated long-range avoidance of interspecific competition by a solitary endoparasitoid may optimize its foraging success
Journal of Insect Science 3 (33), 24-24
XIII International Entomophagous Insects Workshop - July 27-31, 2003, Tucson, Arizona, U.S.A.
Abstract: Solitary endoparasitoids, of which only one can develop per host, are expected to avoid hosts that have already been parasitized by another wasp if it is likely that they will loose the intrinsic competition. We propose, however, that parasitoids that are not egg-limited - they carry more eggs than they would normally lay in their lifetime - should only reject such inferior hosts if they save considerable time that they then have available for the search of more suitable hosts. The competition between sympatric solitary parasitoids allows testing of this time saving host discrimination hypothesis. For this reason, we studied the outcome of competition between the two parasitoids Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae) and Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae). They are the most common parasitoids of larvae of the moth Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) in Mexico and throughout the Americas. In a first experiment, both wasps readily accepted hosts that had already been parasitised by the other species. In these double parasitised hosts, C. sonorensis was found to be the superior intrinsic competitor, independently of the sequence in which the two species parasitised a host and of the time difference between the respective ovipositions. In a second experiment, we studied the outcome of the competition in cages where the wasps could freely forage for 1 day among small maize plants carrying host larvae. Parasitism in these cages with both wasps was compared with parasitism in cages with only one of the two species present. Again C. sonorensis was superior in cases of competition, whereas both species showed similar efficiency in parasitism in the cages in which they were confined alone. In a final experiment, we tested the responses of the wasps to the odour of their competitor in a six-arm olfactometer. Female wasps were confronted with the odours of three sources; 1) maize plants damaged by host larvae, 2) similar plants combined with C. marginiventris females, or 3) similar plants combined with C. sonorensis females. It was found that C. marginiventris females avoided the odour source with C. sonorensis females, whereas C. sonorensis was attracted to all three odour combinations equally. These results are in accordance with our hypothesis of time optimization. Both wasps carry ample eggs and should therefore, upon contact, readily accept inferior hosts, because oviposition takes only seconds. However, by avoiding the odour of C. sonorensis, female C. marginiventris may evade the intrinsic competition, which it almost always loses, and may save considerable time that it can allocate to the search for more profitable hosts.
Database assignments for author(s): Ted C.J. Turlings

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
environment/habitat manipulation

Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.

Spodoptera frugiperda Maize/corn (Zea mays) Mexico
Campoletis sonorensis (parasitoid) Spodoptera frugiperda Maize/corn (Zea mays) Mexico
Cotesia marginiventris (parasitoid) Spodoptera frugiperda Maize/corn (Zea mays) Mexico