Ecological Adaptation Of The Introduced Biocontrol Agent, Agasicles Hygrophila, For Alligatorweed, Alternanthera Philoxeroides, In China

Alligatorweed Altemanthera philoxeroides (Mart.) Griseb (Amaranthaceae)originated in South America is a noxious weed in agricultural, aquatic and otherecologically important habitats in China, particularly the South. With high adaptabilityand a wide geographic distribution worldwide, the weed has aquatic and terrestrialforms depending on the conditions of the niche it grows in.A host specific flea beetle, Agasicles hygrophila Selman & Vogt (Chrysomelidae),originated from South America and found by USDA scientist in Argentina, wasintroduced to China from Florida of USA in 1986 for the biological control of theAlligatorweed. With mass propagation programs conducted by a number ofcollaborating institutes, the beetle has so far successfully established population andhas exerted effective control of the target weed in many areas of South China. Thisdissertation research systematically examined the ecological adaptation of Agasicleshygrophila 13 years after its introduction into China. This is the first time such asystematic evaluation is conducted on the ecological adaptation and impact of anintroduced foreign insect biological control agent against an exotic invasive weedspecies in ChinaSurveys were conducted through mail correspondence in 1019 counties of 22provinces and on-site spot investigations throughout 139 counties of 18 provincessouth. The maps were drawn by GPS and GIS techniques. The weed was found tooccur in regions between longitude 1000 and 1210 East, latitude 18 0 and 350 North,covering 16 provinces. The northern limit of its distribution was found to be the YellowRiver. The introduced biocontrol agent, Agasicles hygrophila was found in regionsbetween longitude 1020 and 1210 East, latitude 200 and 320 North, covering 14provinces. The beetle was not found in Hainan and Henan provinces wherealligatorweed inhabited. It is concluded that the weed distributed in the subtropicalzone while the beetle dispersed in central subtropical and southern subtropical zonesin China.Laboratory experiments were conducted to examine the supercooling point, thefreezing point and the lethal time under cold temperature for the flea beetle. There areno significant difference among supercooling point of egg, larva, pupa, adult, freezingpoint of larva is higher than the others, significantly. It was found that the supercooling6point and the freezing point of the adults were -7.92 C and freezing-4.87 XD,respectively, under 0 C ., 5 C . 0 C -5 C -10 C LT50 of the adults was583.3h,220.34h,37.85h,1.42h,0.01; The LI95 was 1577.8h, 458.79h, 93.46h, 2.85hand O.12h, respectively. No significant difference in the supercooling point, thefreezing point and the lethal time under the cold temperatures was found between theadults of the 1999 samples of the Florida population and the 1999 samples of thepopulations from Chongqing, Fuzhou and Guangzhou of China. The results suggestedthat low temperature, rather than geographical populations, was the key factoraffecting the mortality of the beetle during winter, hence limiting its distributionnorthward in China. But overall, the beetle has well adapted to the ecologicalenvironment in China after introduction in 1986.Based on the results in the adaptation studies and the regional climaticcharacteristics of China, a set of climatic and physiological criteria were proposed forassessing the potential distribution and the control effect of the introduced biocontrolagent. Isotherm 5C in January is the northern limit for the beetle to exert effectivecontrol on alligatorweed. In other words, it could control the weed effectively in centraland southern subtropical zone of China. In the northern subtropical zone of Chinawhere isotherm in January is 4-5C, the beetle would not be able to establish orma...