| In recent years different types of fruit scars were discovered in citrus production area. These scars can reduce the appearance quality and economic value of citrus fruits. In order to discover the reasons of fruit scarring, we have investigated the flower-visiting insects in different citrus orchards, and tested whether the major flower-visiting insects could made scars on the fruits. Since thrips is the major insect species which causes fruit scars, the different species, damages, dynamics and controlling methods of thrips in the orchards were also investigated and tested. The research results were as follows:Based on the investigations, flower-visiting insects in Yichang and Ganzhou citrus production areas were consisted of 91 species, belonged to 7 orders (Thysanoptera, Homoptera, Hemiptera, Coleoptera, Lepidoptera, Diptera and Hymenoptera),41 families. There were 52 species in Yichang citrus orchards. The dominant orders are Coleoptera, Lepidoptera, Thysanoptera and Diptera. These major orders were respectively 30.77%,26.92%,13.46% and 13.46% of the whole species. In Ganzhou citrus orchards, there were 61 species and the major orders were Coleoptera, Hemiptera, Lepidoptera, Thysanoptera and Hymenoptera, accounting for 26.23%,16.39%,16.39%,14.75% and 14.75% respectively of the total species.The experiments about whether flower-visiting insects had influence on citrus fruits demonstrated that thrips, Luperomorpha xanthmdera Frm. and Homona coffearia Nietner could damage citrus flowers or young fruits. Citrus damaged by thrips appeared grayish or silvery scars on the rind. L. xanthmdera Frm. attacked petals, sepals, stigmas and led to indentations. H. coffearia Nietner attacked ovary, stigmas and young fruits, and led to deep indentations with white silk around.11 species of thrips which belonged to 2 families were collected in the two citrus production areas. The 2 families were as follows:the Thripidae (7 species) including Scirtothrips dorsalis Hood, Lefroyothrips lefroyi (Bagnall), Frankliniella intonsa (Trybom), Thrips flavidulus(Bagnall), T. hawaiiensis(Morgan), T. palmi Karny and T. coloratus Schmutz; the Phlaeothripidae (4 species) including Rhaebothrips lativentris Karny, Haplothrips chinensis Priesner, H. subtilissimus(Haliday) and H. tenuipennis Bagnall.The major species in different orchards were various. In Yichang citrus orchards, the major species were T. flavidulus (Bagnall), S. dorsalis Hood and T. palmi Karny. The propotion were 30.77%,28.21% and 23.08% respectively. In Ganzhou citrus orchards the major species were T.flavidulus(Bagnall), T. palmi Karny and S. dorsalis Hood, accounting for 50.94%,20.75 and 14.15% respectively.Based on systmatic investigations, the dynamic of mixed thrips population in citrus orchard during the fruit growing appeared three peaks. The first peak appeared during the florescence period, and the adults occupied a major proportion. The second peak appeared during the mid-May to mid-June in the period of young fruit, and more larvae were found. The third peak occurred during the July and August when new leaves grew on the citrus trees.The study of controlling thrips in citrus orchards demonstrated that the number of thrips decreased significantly in the orchards which were sprayed Imidacloprid 70 WP, Dipterex 30 EC and Avermectin 5 WDG respectively. But the fruit injury rate could be reduced by using the pesticides before the florescence or during the florescence of citrus. Spraying after florescence had no significant effect.The attractiveness of different colors to thrips indicated that thrips had the strongest preference to blue sticky card and deep-blue sticky card. There is a significant difference between these two colors and the other eight colors sticky cards (p<0.01). Experiment was also conducted on the trapping effect of blue sticky card from different directions (east, south, west and north). The results showed that most thrips were trapped from the south, which existed a significant difference with those from west and north directions(P<0.05). |
PDF Full Text Request