Cynipid gall growth dynamics and enemy attack: effects of gall size, toughness and thickness

Abstract

Galling insects have developed many strategies to preclude or reduce the attack by natural enemies, such as an increased wall thickness early in the season, and switching to larger and tougher walls later in the maturation stage. In this study, we observed the efficiency of each one of these parameters in reducing mortality of the leaf galling wasp Atrusca caprone Weld (Hymenoptera: Cynipidae), on Quercus turbinella Greene (Fagaceae), during the three months of gall development (June-August). Gall diameter and wall toughness increased from the first to the third month of the study (ANOVA, Diameter: F = 88.73, p < 0.0001; ANOVA, Toughness: F = 26.13, p < 0.0001). However, gall wall thickness increased from June to July, decreasing in August (ANOVA, F = 35.84, p < 0.0001). Gall survivorship was only 2 % in June, increasing to 10 % in July and to 29.3 % in August. Multiple regression analyses showed that only gall wall toughness influenced gall susceptibility to parasitoid attack (r² = 0.52, F = 13.84, p < 0.01). Gall survivorship was very low in the first month due probably to low wall toughness, which led to a higher success of oviposition by parasitoids during this phase. These results suggest that the first month is critical to gall establishment, and the galls which are not parasitized at this stage are less likely to be attacked later.

Phenotypic matching in ovipositor size in the parasitoid Galeopsomyia sp. (Hymenoptera, Eulophidae) attacking different gall inducers

“…A galler defense strategy, besides investing in thickness and size of the gall (Godfray, 1994), is plant tissue toughness, which is usually associated to gall development along time, since some freshly induced galls tend to be harder (Fernandes et al, 1999). This factor was not evaluated in the present study, since hardness could decrease parasitism rate but probably did not select for ovipositor length.…”

Assessment of Chestnut Gall Toughness: Implications for a Biocontrol Agent

“…Several papers have emphasized the importance of gall characteristics on the success of parasitoids when attacking gall insects, and size, thickness, toughness, and the parasitoid's ovipositor length are considered to be important parameters affecting the parasitoid oviposition rate and success of gall-forming insects [24,25]. Hardening of the gall walls is considered one of the most important deterrents to further attack by parasitoids.…”