A Scanning Electron Microscope study of the pecan phylloxera, Phylloxera devastatrix, with observations on emergence

Abstract

The pecan phylloxera, Phylloxera devastatrix Pergande, is a small, cecidogenic insect found throughout the native range of the pecan tree. Infestations of P. devastatrix have been reported to cause reductions in nut quality and quantity, premature defoliation, and shoot dieback. Galls formed by P. devastatrix are an alternate host for the larvae of the hickory shuckworm, Cydia caryana Fitch. Little information exists on the biology and ecology of this insect. The objective of this study was to examine the emergence patterns of P. devastatrix on different pecan cultivars to determine if variability in bud-break between cultivars effected emergence. This study also provided an opportunity to study gall formation and the life cycle in detail.P. devastatrix overwinter as an egg within the body of the sexual female (Figs. 1 & 2). Upon hatching, the stem mother moves to the bud and begins feeding (Figs. 3 & 4). As the stem mother feeds, a gall begins to form around the insect (Fig. 3). Eggs deposited within the gall by the mature stem mother (Fig. 6) hatch into apterous and alate females (Fig. 7). Eggs produced by these females hatch into sexual males and females (Fig. 8 & 9). After mating, an egg is produced within the body of the female. The female next seeks a place on the tree to overwinter, thus completing the cycle. Stoetzel described the development of the stem mother and apterous and alate females as hemimetabolous (incomplete metamorphosis), and that of the sexual males and females as holometabolous (complete metamorphosis). Gal1s of p. devastatrix are classified as cover galls. The upwalling of the plant tissue around the insect, characteristic of this type of gall, can be clearly seen in the SEM photographs (Figs. 3 & 5).