Population dynamics and sex ratio of two biocontrol agents of water hyacinth

Population dynamics and sex ratio of two co-existing species of Water hyacinth weevils, Neochetina bruchi Hustache, 1826 and N. eichhorniae Warner, 1970 (Coleoptera: Curculionidae) were studied. The weevil attack on Water hyacinth was investigated monthly for four years in different water bodies. The weevil's abundance was affected by temperature, humidity and rainfall. The population of the weevils in general was highest (14.97 weevils/plant) in September when the humidity level was very high (88%) with the average of temperature almost 26°C. The lowest abundance (2.49 weevils/plant) was in January when the temperature was the lowest (15.7°C). The abundance of N. bruchi was significantly higher than the population of N. eichhorinae (1:0.04) in Jabalpur, India. Statistical studies revealed that the sex ratio was in favour of female in both the species (1:0.52 and 1:0.70 for N. bruchi and N. eichhorniae, respectively).