Michael J. Stout, Natalie A. Hummel, Srinivas Lanka, Jason C. Hamm, Anna Mészáros, W. Ray McClain, Marty J. Frey and Gary C. Barbee

Crawfish are Louisiana’s most valuable aquaculture commodity, and Louisiana is the only state that produces crawfish for human consumption on a large commercial scale. Approximately 184,000 acres were devoted to crawfish production in 2010, with a total value of approximately $170 million. Most farm-raised crawfish in Louisiana are produced in parishes in southwest Louisiana, and rice fields and crawfish ponds are often found in close proximity in these parishes; in fact, three of the four largest crawfish-producing parishes in the state are also the largest rice-producing parishes. Moreover, crawfish and rice are co-cultivated by many producers using rotational schemes in which rice fields are transitioned to crawfish ponds by reflooding the rice field after harvest and managing rice stubble for regrowth in late summer or fall.

Crawfish and insects are taxonomically related and share a number of physiological features; as a result, insecticides used to eliminate insect pests such as the rice water weevil can also kill crawfish. In particular, pyrethroid insecticides, which are widely used to control rice water weevils in rice, are extremely toxic to crawfish. There are several routes by which crawfish may be exposed to insecticides applied to rice fields. They may be exposed through drift arising from insecticide applications made to nearby rice fields. In addition, crawfish in ponds used previously for rice production may be exposed to residual insecticides in the soil, and tailwater released from insecticide-treated rice fields may injure or kill crawfish if the water is diverted to nearby ponds.

Since 2005, new insecticides are tested in the laboratory and the field to determine their toxicity to crawfish. Laboratory assays showed that the active ingredients found in the insecticidal seed treatments Dermacor X-100, NipsIt INSIDE and Cruiser Maxx, while still capable of killing crawfish, are approximately 1,000 times less acutely toxic than pyrethroids. Furthermore, in field tests using crawfish stocked in cages in plots treated with the new seed treatments, none of the pyrethroid alternatives caused crawfish mortalities significantly higher than observed in control plots. Overall, LSU AgCenter studies indicate these new insecticides pose much less of a threat to crawfish than do the pyrethroids.

Another way to reduce the effect of rice water weevil management on crawfish is to rely less on insecticides and more on nonchemical tactics such as early planting and water management. Also, LSU AgCenter researchers are trying to develop rice varieties resistant to rice water weevils, which will further reduce reliance on insecticides for weevil management and will increase the safety of Louisiana’s rice fields for crawfish.  

Michael J. Stout, L.D. Newsom Professor in Integrated Pest Management; Natalie A. Hummel, Associate Professor, Srinivas Lanka and Jason C. Hamm, Graduate Students, and Anna Mészáros, Research Associate, Department of Entomology, LSU AgCenter, Baton Rouge, La.; W. Ray McClain, Professor, and Marty J. Frey, Research Associate, Rice Research Station, Crowley, La.; and Gary C. Barbee, Assistant Professor, Department of Life, Earth and Environmental Sciences, West Texas A&M University, Canyon, Texas

(This article was published in the summer 2011 issue of Louisiana Agriculture magazine.)