Biological control of the water hyacinth (Eichhornia crassipes (mart.) solms) in the Southern part of Thailand
1981
Jiraporn Rajpreecha
Biological control of the water hyacinth, Eichhornia crassipes, in the southern part of Thailand was initiated in 1977 with the preliminary survey of the potential natural enemies. A species of grasshopper, Gesonula punctifrons (Stal) and three species of diseases, Atternaria eichhornia, Myrothecium roridrum and Rhizoctonia solani, were found. However, they were not contributing to any substantial control. When the water hyacinth weevils, Neochetina eichhorniae Warmer, which were introduced from Florida, were tested and cleared by NBCRC for release, the consignment was brought to the south for further study and releases at Songkla Lake in 1978. The original consignment consisting of 500 adult weevils and C. 1600 larvae did not perform to a satisfactory level. Four consignments were obtained from NBCRC consisting altogether of 1,190 adult weevils in 1980 and cultured by using a culture pond modified from the ones used at CIBC, West Indian Station. The weevils were proliferating so well that releases were made on the outskirt of Hat Yai where they have become established and been spreading out satisfactorily. Additional releases are now made at Tale Noi on the northern most area of Songkla Lake in Pattalung. So far 800 weevils were used in three releases. The establishment is also being monitored. In addition, 439 weevils for the culture here were also introduced by NBCRC to Sri Lanka early in May 1980 in cooperation with the Plant Protection Service of the Department of Agriculture, Peradeniya, Sri Lanka.
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