1Laboratoire de Neurobiologie Comparée des Invertébrés, INRA, BP 23, 91440 Bures-sur-Yvette, France.
2Laboratoire d'Ecologie Animale et Entomologie, Institut de Zoologie, Université de Neuchâtel, 2007, Neuchâtel, Swizerland.
3Populations et Génétique Evolutive, CNRS, 91198 Gif-sur-Yvette, France.
Based on the highly probable assumption that innate olfactory searching responses, involved in the first search for a host, are crucial for the individual's reproduction probability, this work aims to investigate if the genetic variability of this trait is related to reproduction constraints. We studied the variability of odor-mediated search for Drosophila melanogaster larvae between two strains of their parasitoid, Leptopilina boulardi, differing by their geographic origin: Nasrallah (Tunisia) and Brazzaville (Congo). Ovipositor search in response to the fruit aromas was almost systematic in Brazzaville females but rare in Nasrallah females. Additional experiments showed that the latency of the probing response to banana odor as well as to the presence of larvae was lower in Brazzaville females. The behavior of hybrid females (F1 and F2) showed a genetic transmission of this propensity to probe in response to fruit aromas. The transmission is both chromosomic and cytoplasmic. The intermediate level of response in one hybrid also indicates that the trait is polygenic. The studied traits are strongly heritable because the values of F2 females and their grand mothers are very close and reflect the resemblance of their cytoplasm and nucleus. The cytoplasmic heredity can be linked to mitochondrial DNA or symbiotic microorganisms. The obvious differences in searching activity are linked to identified reproduction constraints and can be viewed as the result of an evolution process.