Comparative studies on biology of Neochetina eichhorniae warner and Neochetina bruchi Hustache (Coleoptera: Curculionidae), biological control agents of waterhyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Liliales: Pontederiaceae, in Thailand
1996
Srijumnun Pichidsuwanchai
Comparative studies on biology and comparative control efficiency of Neochetina eichhorniae Warner and Neochetina bruchi Hustache were carried out both under the laboratory and insectary conditions. N. eichhorniae female produced 478.63+-139.0 eggs which hatched in 7.08+-0.62 days while N. bruchi female laid 630+-186.43 eggs which hatched in 6.69+-0.83 days. The larvae of N. eichhorniae and N. bruchi molted three times and the total larval stages were 30.80+-2.52 and 24.30+-0.90 days respectively. The growth increment of larvae based on the width of head capsules assumed a geometric progression, the ratios being 1.57 and 1.55 for N. eichhorniae and N. bruchi respectively. The pupae of N. eichhorniae and N. bruchi required 14.50+-2.20 and 17.90+-4.28 days respectively for development. The longevity of adult male and female of N. eichhorniae were 147.00+-69.28 and 105.31+-48.68 days. N. bruchi male and female lived for 125.29+-54.03 and 88.73+-28.44 days. The life cycle of N. eichhorniae were 52.3+-3.2 days, and was longer than that of N. bruchi, which was 47.2+-4.45 days. Female N. eichhorniae preferred the pseudolamina and N. bruchi preferred the petioles for oviposition. Adult N. eichhorniae fed 65.47 square mm of waterhyacinth leaves per day, and N. bruchi fed 66.95 square mm per day. The females of both species fed more than the males. The comparative control efficiency, measured by using the number of feeding scars, during summer, rainy season and winter in Thailand indicated that N. eichhorniae, N. bruchi and the combination of both species gave no significant difference in terms of their performance. However, the numbers of feeding scars during rainy season and winter were significantly higher than those in summer.
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