Occurrence of the tea tortrix complex and their parasitoids in pesticide-free tea fields in Shizuoka Prefecture, Japan

The occurrence of the tea tortrix complex and its parasitoids in pesticide-free tea fields from 2006 to 2008 was investigated by using light traps and sticky suction traps, respectively, in order to examine the interaction between them. The numbers of both Adoxophyes honmai Yasuda and Homona magnanima Diakonoff trapped by light traps were observed to decrease from 2006 to 2008, and the rate of decrease in the case of the former was higher than that in the case of the latter. The most numerous parasitoids trapped by suction sticky trap were Trichogramma spp., followed by Apanteles adoxophyesi Minamikawa. Ascogaster reticulata Watanabe and Bracon adoxophyesi Minamikawa were found to be trapped rarely. Although the numbers of both Trichogramma spp. and A. adoxophyesi trapped by sticky suction traps between 2006 and 2007 were observed not to be different, the numbers of them drastically decreased in 2008. The numbers of A. reticulata and B. adoxophyesi were observed to decrease from 2006 to 2008. Particularly in 2008, they were found to be trapped rarely. We also compared seasonal changes in the numbers of tea tortrix complex with Trichogramma spp. and A. adoxophyesi. As a result, the number of trapped Trichogramma spp. adults reached a peak 10 to 28 days (average : 19.9 days) and 2 to 25 days (average : 15.7 days) after the peak in the number of A. honmai and H. magnanima adult females, respectively. The number of trapped A. adoxophyesi adults reached a peak 2 to 48 days (average : 26.1 days) and 1 to 39 days (average : 21.8 days) after the peak in the number of A. honmai and H. magnanima adult females, respectively. In addition, a comparison of the seasonal changes in the number of tea tortrix complex with the number of parasitoids suggested that parasitoids increased after late July-the period in which eggs and larvae of tea tortrix complex are found in tea fields with great frequency. Judging from these results, the application of pesticides should be minimized or selective pesticides should be used after late July to conserve the parasitoids and serve as biological control agents.