Overwintering population density and cold tolerance of Bemisia tabaci in greenhouses and open fields in the Fujian Province

In order to clarify the overwintering mechanisms of sweetpotato whiteflyBemisia tabaci (Gennadius) in open fields and greenhouse vegetable production systems in Fujian Province, China, and to provide a theoretical basis for integrated pest management of B. tabaci, field surveys were conducted at six sites (Jian'ou County of Nanping City; Jiangle County and Sanyuan District of Sanming City; Minhou County of Fuzhou City; Xinluo District of Longyan City; and Longhai County of Zhangzhou City) in January 9-12 and February 21-24, 2017. Sixteen B. tabaci host plants belonging to six families were found, which included the following vegetables:broccoli (Brassica oleracea var. botrytis L.), tomato (Lycopersicon esculentum Mill.), and eggplant (Solanum melongena L.), and broadleaved weeds:Solanum nigrum L., Conyza canadensis (L.) Cronq., Ranunculus sieboldii Miq., and Ageratum conyzoides L. For broccoli grown in open fields, significantly greater densities of overwintering B. tabaci were found in January than in February, and substantially greater densities of B. tabaci were detected on postharvest broccoli residuals than those on broccoli at the rosette and the head development stages. There were significantly higher densities of overwintering B. tabaci in fallow greenhouses than in productive greenhouses. Markedly greater densities of overwintering B. tabaci were found in greenhouses than in open fields, regardless of whether the host plants were vegetables or broadleaved weeds. All life stages for overwintering B. tabaci were found in greenhouses across the province and in open fields in Zhangzhou, but eggs and pseudopupa were found in open fields in the Nanping and Sanming areas, where the temperature was low. Overwintering B. tabaci cryptic species MEAM1 and MED were detected in vegetables; in all, there were 57 and 111 individuals, respectively, of the two cryptic species. We inferred that the usage of greenhouses may promote the establishment of the cryptic species MED in the Fujian Province. We then carried out laboratory experiments to test the cold tolerance of B. tabaci and to test the suitability of broadleaved weeds for the development of B. tabaci. We demonstrated that eggs and old nymphs of B. tabaci could tolerate cold stress better than adults and young nymph. B. tabaci had comparable generational survival rates on broadleaved weeds S. nigrum (79.3%) and R. sieboldii (81.1%), lower than that on B. oleracea var. botrytis (83.6%), a common crop widely grown in Fujian Province during winter. The generational developmental duration of B. tabaci was significantly shorter on S. nigrum (16.7 d) than on B. oleracea var. botrytis (18.9 d), which was similar to that on R. sieboldii (18.8 d), implying that broadleaved weeds serve as important potential alternatives to vegetable crops as host plants for B. tabaci in winter. In summary, B. tabaci can overwinter successfully in the open fields in Fujian Province, and the establishment of greenhouses promotes the development of overwintering B. tabaci.