Exploring alternative management options for rice water weevil (Lissorhoptrus oryzophilus Kuschel) in California

Rice water weevil (Lissorhoptrus oryzophilus Kuschel) is the most deleterious insect pest of rice in the United States. It causes yield losses up to 25% in untreated situations. The majority of the damage comes from soil dwelling larvae that feed on roots as a source of nutrients and oxygen. The main treatments for the weevil in California involve pyrethroid pesticides. Environmental concerns have led to a need to explore alternative strategies. It was observed in the 1990s that straw incorporation and winter flooding led to a reduction in the number of weevil larvae sampled in fields. The goal of my research is to establish winter flooding and straw incorporation together as a viable non-chemical option for growers to reduce weevil populations and to determine the possible mechanisms behind it. I hypothesize the following mechanisms are causing direct or indirect harm to weevil larvae in the rhizosphere: a) toxic gas production such as hydrogen sulfide or methane b) degradation products that interfere with the larva’s ability to hold a thin air layer for gas exchange or c) toxicity from heavy metal mobilization under anoxic soil conditions. Experiments were carried out in the summer 2012 to answer the first two questions. Data will be discussed.