Distribution of Wax Gland Pores on the Body Surface and the Dynamics of Wax Secretion of Wooly Apple Aphid Eriosoma lanigerum (Hemiptera: Aphididae)
2016
Su, Min | Tan, Xiumei | Yang, Qinmin | Wang, Jiqing | Wan, Fanghao | Zhou, Hongxu
Eriosoma lanigerum (Hemiptera: Aphididae) is an important invasive pest causing serious damage to apple trees in many countries. The powdery wax covering the integument of this aphid plays an important role in its defense against natural enemies. We examined all instars and adults of E. lanigerum to determine the morphology and distribution of wax gland pores. We found four lines of wax-gland plates, two pleural and two marginal, on all thoracic segments and on the first seven abdominal segments. On the head, there are six pleural and two marginal plates on the first, while the eighth abdominal segment had just two pleural plates. In total, 50 wax gland plates were distributed over the dorsal region of the aphid. Each plate was composed of several wax gland pores arranged in a circle, with from 3 to 12 “petals.” On average, abdominal segments had 8 to 12 pores, thoracic segments had 7 – 10 pores, and the head had 5 – 8 pores. The wax secreted by different instars varied, and the optimal time to observe wax secretion in 1st to 4th instars and adults is at 16, 12, 8, 4 and 2 hours respectively after removing the wax on the cuticle. The rate of wax secretion increased with age, correlating with increases in body length, width, and diameter. In 1st to 3rd instars, marginal plates secreted more wax skeins and bundles of wax skeins than pleural plates, but there were no statistically significant differences between pleural and marginal plates. For 4th instars and adults, no significant differences were found in the number of wax filaments between pleural and marginal plates. For all E. lanigerum instars, more wax was found on the abdomen than on other parts of the body, which might help protect woolly apple aphids against honeydew, rain and parasitism.
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