Han Baoyu

Probing behavior of the tea green leafhopper on different tea plant cultivars

Abstract The probing behaviors of the tea green leafhopper, Empoasca vitis (Gothe), on 9 tea cultivars were studied using video-text Direct Current-Electrical Penetration Graph, i.e., DC-EPG. The following 7 types of waveforms produced by the leafhopper stylet probing were determined: A, stylet pathway formation; S, salivation when stylets pierce into and stay in phloems; C, active ingestion before stylets reach phloems; E and F, passive ingestion in phloems; R, the insect resting with its stylet inserted into the leaf tissue and NP without probing. The 9 tested tea cultivars were categorized into 3 groups by the cluster analysis according to the number of probes per insect, waveform durations, or duration per probe of various waveforms on different tea cultivars. Waveforms S, E and F correlated to the main feeding activity of the leafhopper and may provide valuable information on predicting the resis-tance level of the tea plants to the leafhopper. The resistance level of the 9 tea cultivars to the leafhopper was ranked based on the durations of waveforms S, E and F, as well as the duration per probe including various waveforms. The ranking order of the resis-tance was: Longjingchangye > Hangdan > Zhenghedabaicha > Qianmei 601 > Hongyafoshuo > Zhongcha 102 > Zhongcha 302 > Longjing 43 > Anjibaicha, which corresponded to the resistance level determined by the population density (infestation) of the leaf-hopper on the 9 tea cultivars in the tea fields. Our study suggests that this simple and convenient DC-EPG technique might have great potential as a reliable tool to predict the resistance of tea cultivars to the tea leafhopper.

EAG and behavioral responses of the wingless tea aphid Toxoptera aurantii (Homoptera: Aphididae) to tea plant volatiles

Abstract Electrophysiological and behavioral responses of the wingless tea aphid, Toxoptera aurantii (Boyer), to 14 synthetic volatiles identified from tea shoots, their partial (GLV mixture) and full (ACB mixture) blends, and fresh young tea leaves, buds, tender stems, adult tea leaves and tea aphid-damaged young leaves (ADYL) were studied by using an electroantennography (EAG) and a four-arm olfactometer. ACB elicited the largest EAG responses. Major volatile components, Z -3-hexen-1-ol, E -2-hexenal, n-hexanol, methyl salicylate and benzylalcohol, from the tea shoots were strongly EAG active. All the 4 tested tea shoot tissues also elicited significant EAG responses, with the young tea leaves being the strongest, followed by buds, tender stems and adult tea leaves. Surprisingly, ADYL elicited a weakly negative EAG response. In the olfactory assays, the fresh and tender tea leaves, as well as the individual major volatile components, e.g. Z -3-hexenyl acetate, methyl salicylate, E -2-hexen-1-ol and Z -3-hexen-1-ol, from the tender shoots (EAG-active) were all attractive. This result might indicate that the wingless tea aphids may use tea shoot volatiles as kairomone to find their optimal feeding sites, e.g. fresh tender tea shoots.

Complete mitochondrial genome of the tea looper caterpillar, Ectropis obliqua (Lepidoptera: Geometridae) with a phylogenetic analysis of Geometridae

The complete mitochondrial genome (mitogenome) of the Ectropis obliqua (Lepidoptera: Geometridae) was sequenced and compared with other species of Geometridae. The mitochondrial genome of E. obliqua is 15,475bp long and contains 37 genes including 13 protein coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes and an A+T-rich region. Gene cluster trnI-trnQ-trnM rearranged to trnM-trnI-trnQ comparing with the ancestral mitogenome of insects. All tRNA genes have typical cloverleaf secondary structure except for trnS (AGN). All the sequenced mitogenomes from Geometridae have negative AT-skews and positive GC-skews except for Biston suppressaria. The synonymous and nonsynonymous substitutions ratios (Ka/Ks) indicated variable selective pressures among 13 PCGs. The phylogenetic relationship among 11 species of Geometridae was recovered based on 13 protein coding genes and 2 rRNA genes using Bayesian inference. E. obliqua is grouped with other Ennominae species and recovered to be sister-relationship with Abraxas suspecta.

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

Abstract 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.