[The influence of road dust on Aspidiotus nerii (Homoptera Diaspididae) and its main parasite Aphytis chilensis (Hymenoptera Aphelinidae) on olives.] (in French)

In 3 localities in Crete, Greece, the population densities and compositions of A. nerii and its parasite A. chilensis were studied in relation to the road dust found in the 1st 3 lines of olive trees along unpaved roads. As the dust density decreases the population density of the scale diminishes from 23.0 to 3.1 scales/leaf and is at a very low level in the interior of the orchard. The proportion of scales killed by unknown causes and the percent parasitism increase from the road towards the interior. Scale mortality is attributed to the host-feeding activity of the female parasite. A regression analysis suggested that 1.30 scales in the preoviposition stage and 1.07 ovipositing scales are killed through host-feeding for each egg deposited by the parasite. The immature stages of the parasite are not affected by dust or host-feeding. Laboratory experiments where branches from potted olives were treated with road dust indicate that the dust gives 13 times higher fixation of the crawlers. On squash with dust bands, where the crawlers can choose the substrate, this value exceeds 40. This observation is now used in the insectary to improve fixation of the crawlers, by dusting the squash with talc prior to infestation. Under equal scale densities the parasite prefers clean host over dusted by a factor of 2.9. High infestations along some roads are caused by the dust which facilitates fixation of the crawlers. High population levels are maintained because the activity of the parasites is reduced in the presence of dust. A. chilensis, which maintains 23-25% total parasitism under scale densities ranging from 3.1-8.9 scales/leaf, is responsible for controlling its host below an economic level in the interior of the orchard.