Document: PRE-3-48-24

Implications of within-host carbon uptake patterns on the distribution and performance of a cynipid gall-former.

GALUSKY, P.* and J.R.OTT

Southwest Texas State University, San Marcos, TX, 78666, USA ¹

Abstract:
The host vigor hypothesis (HVH) predicts that phytophagous insects preferentially feed on relatively vigorous plants (or vigorous shoots within a plant). We tested the HVH by comparing the observed within-canopy distribution of galls induced by Belonocnema treatae (Cynipidae: Hymenoptera) with the distribution predicted by the pattern of carbon uptake of the host plant. Quercus fusiformis exhibits differential rates of carbon uptake within its canopy by both strata (upper > mid > lower) and compass direction (SE > SW = NE > NW). The within-plant distribution and performance of two consecutive gall-former generations were sampled for the 3 strata and 4 compass directions on 16 trees. At each of the 12 strata x direction sites/tree, ovipuncture density, initiated gall density, gall size, and gall-former performance (# mature galls/ovipuncture) were estimated from a random sample of 100 leaves (total 1200 leaves per tree). Three-way ANOVA was used to test for main and interaction effects of direction, strata, and host plant on ovipuncture density, initiated gall density, gall size, and performance. Gall and ovipuncture density were highest in the low stratum; and conversely, performance was highest in the upper stratum. These results suggest that larval performance is enhanced on relatively vigorous regions within host canopies; but contrary to HVH predictions, preferred oviposition sites at this scale are not correlated with performance. The contradiction may be an artifact of spatially constrained gall-former attack strategies.

Keywords: Cynipidae, host vigor, within-plant distribution

This abstract is being presented at: 3:15 PM in session:
Oral Session #15: Parasitoids and Diseases.