Preference of the parasitoid Diachasmimorpha longicaudata for host habitats

DIEGO F. SEGURA; MARÍA F. RODRÍGUEZ; MARIANA M. VISCARRET; SERGIO M. OVRUSKI; JORGE L. CLADERA

Salvador de Bahia, Brasil.

Congreso; 7th International Symposium on Fruit Flies of Economic Importance.; 2006

The potential hosts of Diachasmimorpha longicaudata, a generalist parasitoid of fruit fly larvae, could be hidden in a large number of fruit species (host habitats), and chemical cues play an important role in finding them. We study here the preference of female parasitoids, comparing different host habitats and larval densities, and analyzing the influence of associative ability on  these preference patterns. For this purpose, we used an Y-shaped glass tube olfactometer, at the end of which, two options where simultaneously offered to an individual female parasitoid. A constant airflow of 400 ml/s carried volatile compounds from two odor sources. Tº, RH, and light conditions (respectively, 26±1°C, 70±5%, and 1200luxes) were registered inside the Y-tube. First, we offered at the end of the Y-tube four fruit species (apple, fig, orange, and peach) in pairs; thus 6 possible combinations were analyzed. One naïve female, 7±2-days-old, was released inside the Y-tube, and observed. We registered her choice only within the first 10 min, removing the fruit and washing the Y-tube, every five tested females. The results showed a clear preference pattern in naïve females. Fig was preferred over the other three fruit species, followed by peach, orange, and, finally, apple. We compared preferences between fruit with high and low levels of larval infestation. When females were offered two fruits of the same species differing in larval density, they preferred to visit the one with higher infestation. We tested then if the pattern of preference found in the first experiment may be affected by the degree of infestation (larval density) of the fruit. We found that the pattern of preference of orange over apple is reverted when apples have higher density of larvae than oranges, and it is exacerbated when oranges have higher infestation density than apples. Finally, we analyzed the effect of the previous oviposition experience associated within a given host habitat species on the females’ preference pattern. During three consecutives days, we exposed females to host larvae contained in a substrate made of either orange or apple pulp. On the fourth day, we offered these females one ripe not infested fruit of each species in either arm of the olfactometer. We found that the preference for orange was reverted in favor of apple after females oviposited on larvae in apple pulp, so associative learning of odors seems to be present in this parasitoid. In conclusion, we showed that D. longicaudata females exhibit a strong preference pattern among four host habitats (fruit species) but also that other factors, as infestation level, and previous experiences, are able to modify the choice of naïve females.