| Citrus aphids, a class of important citrus pests that infest new citrus shoots, are becoming more and more serious and pose a great threat to citrus production due to the adjustment of planting structure, global climatic changes and increasing insecticide resistance. To better understand and improve the control strategies of citrus aphids, we performed a two-year field survey for the occurrence of citrus aphids and the regulation of natural enemies in Hubei Province. By combining morphological and molecular identification methods, the main species of aphids and their natural enemies including predators and parasitoids were identified for the field-collected mummies. In addition, the population dynamics of dominant aphids and main predators in Hubei citrus orchards were also investigated. The influence of climate factors on aphids’ population dynamics and the relationship between aphids-natural enemies were investigated. The main results are as follows:1 The identification of citrus aphids species in Hubei Province Through morphological and molecular classification methods and the successive field survey, the results indicated the occurrence of five main citrus aphid species including: Aphis gossypii, Aphis spiraecola, Toxoptera citricidus, Toxoptera aurantii and Aphis craccivora. The methods combining morphological and molecular classification for aphid species identification are high feasible. A simple dichotomous key was established for aphid identification in the field orchards.2 The dominant aphid population dynamics and correlation analysis with the climate factors Toxoptera citricidus and Aphis spiraecola were dominant species in Hubei province, there are several peaks per year, mainly in summer and autumn. In Xianjian village, Aphis spiraecola was the dominant population in 2014, while Toxoptera citricidus became dominant in 2015, which damaged and occupied the main niche alternately. Toxoptera citricidus was the main aphid population throughout the year in HuazhongAgricultural University campus and Yiling area. Climate factors had important impacts on aphid population dynamics either in summer or in autumn.3 Species identification and population dynamics of predators, and correlation analysis with aphid population dynamics There are various kinds of predators preying citrus aphid, including at least 2 classes, 5 orders, 9 families and 21 species, mainly included spider, ladybug, hoverfly, lacewing, stinkbug and so on. All of them had a good control ability against citrus aphids. The population dynamics of natural enemies increased or decreased following the fluctuation of aphids population dynamics, showing a closely positive correlation. The population dynamics of natural enemies followed aphids in 2014; in 2015, there were a large number of natural enemies before the starting period of aphids,which controlled aphid under a low level, but aphids increased when cannibalism phenomenon happened among these natural enemies. Overall, the prey ability of any one predator was lower than them together in pest control.4 The occurrence of parasitoids-hyperparasitoids, and their interactions There are at least 11 species parasitoids identified in Hubei citrus orchards, including 5 primary parasitoids Lysiphlebus testaceipes Cresson, Lysiphlebus fabarum Marshall, Lysiphlebia japonica(Ashmead), Aphidius colemani Vierick, Aphelinus sp. and 6 hyperparasitoids, Syrphophagus sp., Pachyneuron sp., Asaphes sp., Dendrocerus sp., Alloxysta sp., Phaenoglyphis sp.. Aphelinus sp. and Lysiphlebus testaceipes were the main force to control aphids. The main emerged period of all parasitoids is in October, November, May, June, and July. Primary parasitoids beard a significant risk from hyperparasitoids when eliminating aphids. Aphids’ development and population dynamics were related to different ecological conditions, which consequently affected the primary parasitoids’ pest control capability and risks from hyperparasitoids. |
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