BIOLOGICASal STUDIES ON Neochetina eichhorniae AND Neochetina bruchi, TWO SPECIFIC WEEVIlS FOR CONTROlliNG WATER HYACINTH

Abstract

Studies were carried out on two beneficial monophagous specific weevil species, Neochetina eiclzlwrniae and N bruchi, worldwide used for the biological control of the most serious aquatic weed, water hyacinth Eichhroniae crassipes. Experiments were carried out outdoors in wire screen cages of about 40 m3 to find out the role of N. bruchi in saving water loss through evapo-ranspiration by water hyacinth and in reducing the rate of flowering by this weed, and also for studying the biology of the two Neochetina species. Infestation to water hyacinth by N. bruchi for 14 successive

weeks reduced the water loss by 39% as overall average than that lost by the healthy uninfested plants. The reduction rate in water loss during the last week (week 14th) reached 74%. Infestation by Neochetina weevils reduced the rate of flowering by E. crassipes by 47.8% in the third week and this rate increased to 87% in the 9th week of experiment. Eggs, larvae and pupae of N. eichhorniae and N. bruchi were

described and their durations were recorded. The total developmental period reached 69 days for N. bruc/zi and 88.3 for N. eichlwrniae at means of 28°C and 58% R.H. At 27°C. and 59% R.H., a single mated female deposited 191.5 (162 - 256)eggs throughout 30 days oviposition period. From the life-table computer analysis, the generation period was 79.98 days, females occupied 50% of total population, and 65.5 days represented the time from oviposition until mortality of 50% of population.