| In recent years different types of citrus fruit scarring were widely discovered on the navel oranges in the Gannan area citrus orchards. These fruit scars seriously effect the appearance quality of citrus fruits. In order to improve the quality of citrus fruit, we have investigated the reasons for fruit scarring in this study. We also investigated the pest which causes citrus fruit scarring in citrus orchards. We first determined the Thrips flavidulus (Bagnall) which causes citrus fruit scarring in Gannan city, Jiangxi province, China. Furthermore, the damage characteristics, occurrence regularity, experimental population life table and controlling efficiency were also studied and assessed the attractive of volatile plant compounds to T. flavidulus. The results were presented as follows:The result showed that there are11species of thrips in Gannan citrus orchards. The major species were T. flavidulus, Thrips palmi Karny and Scirtothrips dorsalis Hood. Their occurrence percent were53.25%,18.46%,15.46%in2011and50.94%,20.75%,14.15%in2010respectively. The only thrips that damage citrus fruit are those that feed on the developing fruits, not those that feed only on pollen and floral tissues. T. flavidulus and Frankliniella tenuicornis (Uzel) are the species that known to feed on very young citrus fruits. Thrips abundance peaks in citrus orchards during the main flowering period in spring. The thrips feed on and damage citrus petal. The females lay eggs on flower, young fruit and other parts, young fruits, especially during the2to4weeks after the petal fall, are the favorite food of the thrips. The larva thrips feed together under the calyx and result in a characteristic sliver grey and ring-shaped scar around the stem end of the fruit. The scar expands outward from the calyx as the fruit grows.In the laboratory, T. jlavidulus was reared on the kidney bean at the designated temperatures (22℃,25℃,28℃,31℃and34℃) and75%RH to determine its development period, survival rate, fecundity, life history parameters, development threshold and effective accumulative temperature. The data showed that the development duration of T. flavidulus decreased significantly as the temperature increased from22℃to34℃. The largest number of eggs was oviposited by the female in22℃. The highest oviposition rate was detectedin25℃and28℃. The number of eggs laid per day peaked shortly after the beginning of the oviposition period. The net highest reproductive rate (R0) was found in25℃. The generation time (T) and doubling time (t) was shored gradually with the increase of temperature. The intrinsic rate of increase (rm) and the finite rate of increase (λ) increased with the rise of the temperature. The development threshold of egg,1st instar,2st instar, prepupa, pupa, adults stages and the whole generation were8.45℃,6.78℃,8.67℃,8.7℃,10.34℃,10.50℃and9.75℃respectively. The effective accumulative temperature was296.06day degree. The number of generation of T. flavidulus was13-14generations in Gannan city in2010.The behavioral responses of thrips to the sticky cards in different colors including blue, yellow, blue-deep, white, red, green, purple, gray and pink were in citrus orchards. Our results indicated that the thrips significantly preferred the blue and deep-blue sticky cards to the other eight color sticky cards (p<0.01). Moreover, the sticky cards placed in the south significantly trapped the greater number of thrips than those in eastward, westward and northward directions (p<0.05). Four blue sticky cards were set up at the heights of60,120,180and240cm from the ground to trap thrips, when the average height of citrus was approximately220cm. Significantly more thrips were trapped by sticky cards placed at120cm above ground level than those placed at60,180and240cm. Signficantly more thrips were trapped on sticky cards spaced at intervals of4and5m than on cards spaces at intervals of2and3m. During5continuous2-hour spans from8am to6pm, the numbers of thrips trapped were not significantly different. The result indicated that blue sticky cards3days,6days and12days were41.5%,53.9%and37.7%respectively.The behavioral responses of adult female thrips to16different plant volatile compounds evaluated with a Y-tube olfactometer. It was found that thrips performed various chemotaxis to the different tested volatile compounds and the responses presented with dose-dependent. The compound A and E have the significant attraction for thrips at concentration10%and1%. Collectively, the result showed that thrips had significant taxis to the compounds such as benzenoids and monoterpenes isoprenoids. attractant effect of,E, G, J and N at concentration10%for thrips were76%,85.3%,76%,80%and72%repectively.The attractant effect of compound A and J at concentration1%for thrips were70.6%and76%repectively. We select the active substance which has significantly attractive to thrips from benzenoids and monoterpenes compound, to provide a theoretical basis for future thrips pollution prevention and control research. |
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