Lissorhoptrus oryzophilus

Rice water weevils go through 1 generation in Japan and California, but in parts of southern China and the southern US they will undergo up to 3-4 generations per year. The adults feed on leaves and the sheath leaving diagnostic feeding scars which can help gauge the severity of an infestation. the adults will lay eggs beginning in March through May depending on the latitude. The larvae feed on the roots, which is the cause of yield reduction in rice. The loss of roots, reduces the number of plant tillers, which are the panicle bearing structures of the rice plant. Reduction in tillering leads directly to yield loss. In case of strong infestations yield losses can reach 30%.

The adult undergo diapause during the winter from November through March at the foot of perennial grasses or under vegetative cover. When the temperatures overcome the 21 °C, they migrate toward the rice fields either by crawling off levies or flying into fields. Adults are most active in the late afternoon or evening when temperatures are higher than 26 °C and wind speeds are less than 5 mph.

Rice water weevils can be monitored by examining field edges for leaf scarring. Adult populations can be estimated using floating barrier traps. The best way to quantify populations of rice water weevil that can be directly related to yield losses is through soil coring (Way and Espino 2014).

Managing rice water weevil depends on the region and its ecology. In the Southern US, growers use drill seeded systems that allow them to delay planting or flooding of the rice fields. This allows rice plants to grow larger and better tolerate rice water weevils. Southern rice growers also use seed treatments with thiamethoxam (Cruiser) that also help In California, the best methods are treating field edges, rebuilding levees, winter flooding, and foliar spraying with pyrethroids such as lambda-cyhalothrin (Warrior) or neonicotinoids such as clothianidin (Belay). The spraying of insecticides is the cheapest option available to growers.

Host plant resistance has been investigated in rice but results have been less than desirable. Since the 1960s, out of 10,000 lines tested, only 2 showed moderate resistance to rice water weevil feeding. The 2 lines had poor agronomic traits, which led to their discontinued use.^[3]

http://jipm.oxfordjournals.org/content/5/4/D1 Archived 2015-02-13 at the Wayback Machine