POTENTIAL GEOGRAPHICAL-DISTRIBUTION OF ALLIGATOR WEED AND ITS BIOLOGICAL-CONTROL BY AGASICLES HYGROPHILA

Alligator weed is a South American species that has invaded all continents except Africa and Europe and is spreading in Australia where it grows in both aquatic and terrestrial habitats. A climate matching program, CLIMEX, and the known distribution of the weed in South and North America were used to infer areas suitable for its growth elsewhere in the world. Results indicated that most eastern and southern areas of continental Australia are suitable, as are areas of Africa and southern Europe. Classical biological control, using the alligator weed flea beetle Agasicles hygrophila, has been effective in controlling aquatic growth of the weed in many areas in USA. CLIMEX parameter values were also fitted for this beetle using the distribution of the beetle in its native range. The fitted values were validated using the known distribution of the beetle in USA and CLIMEX was then used to find other areas of the world climatically suitable for this insect. A. hygrophila controls alligator weed over part of the weed's range in USA. This information was used to determine a threshold value of the Ecoclimatic Index (EI) produced by CLIMEX, above which effective control was likely. The results indicated that control of alligator weed by the flea beetle would be restricted compared to areas at risk of invasion by the weed. Such predictions are being used in Australia to predict spread and efficacy of agents and to assist control planning and management of alligator weed.