Rhythm of honeydew excretion by the tea aphid and its attraction to various natural enemies

The rhythm of honeydew excretion by the tea aphid Toxoptera aurantii (Boyer) and its attraction to following 9 species (or subspecies) of beneficial insects, Aphidius sp., Chrysopa sinica Tjeder, Chrysopa septempunctata Wesmael, Sphaerophoria menthastri L., Coccinella septempunctata L., Leis axyridis (Pallas) ab. bimaculata Hemmelmann, L. axyridis (Pallas) ab. conspicua Faldermaenn, L. axyridis (Pallas) var. spectabilis Faldermaenn and L. axyridis (Pallas) var. novemdecimpunctata Faldermaenn, were investigated. Forty-five wingless virginoparae nymphs, reproduced by the same wingless virginogenia adult within 1 h, were introduced onto tea seedlings with one aphid per seedling. The honeydews excreted from different instars of nymphs and adults were collected under 21°C, 85% RH, 3500 lx and 12 L:12 D photoperiod. It took 32.4 d ±5.8 d for the tested tea aphids to complete the development of their nymph and adult stages, during which 325.6±35.8 droplets (ca. 41.98 μl ±6.14 μl and 45.34 mg ± 8.76 mg) of honeydews were secreted. During the 1st and 4th instars, there was a logistic regression relationship between the amount of honeydews excreted and the time (days). The honeydew secretion during the first two instars was less than that from the later instars. Adult aphids survived for 22.0 d ± 0.0 d, and excreted 176.31 ± 22.38 droplets (ca. 30.38 μl ± 5.32 μl) of honeydews in a rate of 1 drop per ca. 30–50 min for 5–8 h with a pause for 2–5 h before next secretion series. A batch of forty-five virginoparae female adults, reproduced by the same virginoparae female adult within 1 h, were introduced onto the tea seedlings (one aphid/seedling) under 13–21°, 85% RH, 3500 lx and 12 L:12 D photoperiod. Temperature showed a significant effect on the amounts of honeydews excreted within the range of 13–21°. Honeydews excreted by the aphids significantly increased the searching and retention time of the tested 9 species of natural enemies in a positive dose-response fashion. The searching times of Aphidius sp. and S. menthastri were the longest and the shortest, respectively, among all the 9 species, while the searching and retention time of L. axyridis (Pallas) var. spectabilis was the longest among the four varieties of L. axyridis. Tea aphid oneydew is considered as an important contact kairomone for the tested natural enemies.