Studies On Feeding Preference And Growth Adaptation Of Alligatorweed Flea Beetle (Agasicles Hygrophila) To Different Genotypes Of Alligator Weed (Alternanthera Philoxeroides)

Biological invasions are believed to be the second largest cause of current biodiversity loss, after habitat destruction. As international trade increases, the number of both accidental and intentional exotic introductions is likely to increase. Biological invasions by non-native species have become a major environmental problem and a focus of ecological research.To limit the impact that exotic species have on natural and man-made communities, we need to understand the major mechanisms that allow exotics to become invasive. Alligator weed, Alternanthera philoxeroides(Msrt.)Griseb originated in South America and was introduced to China in 1930', then its population grow quickly in several dozens years. Now it has become one of the most obnoxious weeds in many areas of South China and caused a series of terrific problems.A host specific flea beetle, Agasicles hygrophila Selman & Vogt, originated from South America and found by USDA scientist in Argentina, was introduced to China from Florida of USA in 1986 for the biological control of the Alligatorweed, but it seems not effective. There are several ecotypes of alligator weed in its native region, and the degree damaged by Agasicles hygrophil differed among each genotype. These results have been found in previous studies, but they did not give the reason. Some researchers discussed invasive mechanisms from the characteristics of the plant itself and also had study on adaptation for alligatorweed between aquatic and terrestrial. But only one genotype did they used. In view of these, we compared preference and adaptation of flea beetle to 6 genotypes from native (Argentina) and invasive (China and America) regions. We can conclude that:1) The density of Agasicles hygrophil on a particular host plant genotype depended both on its oviposition preference and on its offspring performance (larva surviving, larva development, pupation et al.) on this plant; Agasicles hygrophil preferred to lay their eggs on plant which their offspring perform best, and there were positive relation between preference and shoots grow rate. We were supported by the popular Optimal Oviposition Theory.2) Using a common garden approach, we compared 6 genotypes from native (Argentina) and invasive (China and America) regions. The results showed that genotype of alligatorweed in China did not evolve change in allocation from defense to growth. That means the genotype in China neither allocated more resources to growth nor less resources to growth defense. Thus the success of invasion in China did not attribute to Evolution of Improved Completive Ability (EICA).The relationship of 6 genotypes from native (Argentina) and invasive (China and America) regions was discussed in our studies by comparing preference and adaptation of flea beetle on them. It not only imply some invasive mechanisms of alligatorweed in China, but also give some date support to biological control.