First report of establishment of two weevils, Neochetina bruchi and Neochetina eichhorniae Warner (Coleoptera: Curculionidae), released against water hyacinth [Pontederia crassipes Mart.] in the Philippines

Abstract

Water hyacinth, Pontederia crassipes Mart. [syn. Eichhornia crassipes (Mart.) Solms.] of the family Pontederiaceae, is one of the world’s worst aquatic weeds and a major problem in the Philippines, covering lakes, and blocking drainage and irrigation canals. Two weevils Neochetina bruchi Hustache and N. eichhorniae Warner (Coleoptera: Curculionidae) were introduced into the Philippines in 1992 to help control this weed. However, their establishment has never been confirmed.

In 2014, P. crassipes infestations at Laguna de Bay and Sampaloc Lake, San Pablo City were inspected but there were no signs of the beetles’ presence, as indicated by distinct feeding scars. During weed surveys north of Manila during February 2023, feeding scars typical of Neochetina spp. were seen at San Quintin, Pangasinan although no beetles were seen. However, at several other sites, namely Baler, San Jose, Maria Aurora and Pulong Bahay, both N. bruchi and N. eichhorniae were found. To our knowledge, this is the first official record of both weevils establishing on P. crassipes in the Philippines and gives prospects to the biological control of this weed in the country. Sets of both weevils have been deposited at the Museum of Natural History, University of the Philippines at Los Baños, Philippines.