Population ecology of Forda riccobonii (Hemiptera: Pemphigidae) on Pistacia atlantica

Abstract

This paper discusses research on the population ecology and biology of the galling aphid Forda riccobonii [Stefani] on Pistacia atlantica Desf. trees in natural habitats in the northern region of Israel. 427 trees were searched for the presence of secondary galls produced by the second (F2) generation. This species occurred on only 29 trees in 7 of the 12 research sites. In the galled trees, a mean of only 22. 7 galls ± 6. 30 (SE) was located in 20 randomly selected branches. Of the 658 galls found, 65% populated the periphery of the crown, while the remaining ones were within. None were found higher than 4 meters above ground level, and they were dispersed evenly in each of the four cardinal directions. The distribution of the galls among the leaves on the galled shoots was not random: the aphids attacked the leaves that developed in the midseason (July) more than the others. Gall size varied greatly, depending on the number of chambers they comprised, from one to ten. Ahigh correlation was found between the number of chambers in the galls and the reproductive success of the F2, as measured by the number of winged aphids in autumn: a mean of 62 ± 2. 5 offspring (range: 47–81). Compared with other galling aphids in Pistacia, relatively few galls (19%) were occupied by predators, parasites, or inquilines. Of these, parasitoid wasps comprised more than 50%. Even so, the colonies in the parasitized galls succeeded in producing the same mean number of offspring as those living in intact galls. Observations indicate that F. riccobonii is less common in natural habitats than previously presumed. The specific morphology of its secondary galls, which consist of relatively closed chambers, seems to provide suitable protection from large enemies. Their relatively wide shape enables the production of a larger number of offspring compared with other galling aphid species that create two different galls in P. atlantica trees during their life cycle.