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http://ucanr.edu/sites/UCRiceProject/

Winter is a good time to catch up on scientific reading. On a paper published in the Journal of Economic Entomology last year, Chinese scientists determined that certain insecticides used in rice (in China) are compatible with the wasp Trichogramma japonicum, a parasitoid of eggs of lepidopterans (moths). Among the insecticides classified as safe to the parasitoid were pyrethroids, insect growth regulators and neonicotinoids. Organophosphates and carbamates were classified as toxic and not very compatible with the wasp*.

Trichogramma wasps are very small, and present in many crops as parasitoids of insect eggs. I have collected them from lepidopteran (stem borers) eggs from rice in Texas. I don't know if they are present in California rice parasitizing our lepidopterans (armyworms); I'll have to collect some armyworm eggs and see if I can recover some.

The article made me think about how insecticides are used in California rice. We have two species of armyworms commonly found in rice late in the season. These two species can feed on rice foliage and panicles, but seldom injure rice to the point of producing yield losses. There might be several reasons for this. One is that at the time of infestation, rice has abundant foliage and the armyworms would have to consume a lot of it to cause a yield reduction. Another reason, and maybe the main one, is that there are several other organisms in a rice field that will feed on the armyworms and limit their population growth. There are two important wasps that parasitize these armyworm larvae. Their cocoons (which are formed after the wasp larvae have consumed the armyworm larvae) are commonly found in rice fields. 

Cocoon of the parasitic wasp Hyposoter exigua.

Coccons of the parasitic wasp Apanteles militaris.

Other organisms feeding on armyworms are spiders, beetles, bugs, even birds. There are probably egg natural enemies too, but I don't think they have been thoroughly documented yet. This abundance of natural enemies is in part the result of the judicious use of insecticides in California rice. Most insecticide applications are done early in the year, when the populations of natural enemies have not built up yet, but pest populations are starting to move in. Additionally, applications are mostly done to field borders, and not entire fields, leaving untreated areas that natural enemies may use as “refuges”. Also, the main type of insecticides currently used in California is the pyrethroids; these have replaced the organophosphates and carbamates that were commonly used in the past.

*Zhao, X. et al. 2012. Assessment of toxicity risk of insecticides used in rice ecosystems on Trichogramma japonicum, an egg parasitoid of rice lepidopterans. J. Econ. Entomol. 105: 92-101

A UC Cooperative Extension specialist says there isn't enough scientific evidence to warrant consumers making changes to their diets nor to their children's diets based on recent media reports about levels of arsenic in rice. The issue arose from an analysis byConsumer Reports of white and brown rice from around the world and rice products like rice cereal, rice milk and rice pasta.

“In virtually every (rice) product we tested, we found measurable amounts of total arsenic,” said the article.

However, Carl Winter, UC Cooperative Extension specialist in the Department of Nutrition at UC Davis, said it's too early to recommend any changes in diet because of these findings.

“Arsenic is a naturally occurring element, found in a lot of different foods and some drinking water at different levels,” Winter said. “We've been consuming it all our lives. It's too early to say whether it is causing any harm.”

He suggests people continue to eat a balanced diet that includes a wide variety of foods while the federal officials who are charged with protecting the United States' food supply draw scientific conclusions about dietary arsenic exposure.

The U.S. Food and Drug Administration is currently collecting thousands of samples of rice-containing foods to develop a database that will allow the agency to establish acceptable levels in foods. Preliminary data released by the FDA in September found that the average levels of inorganic arsenic to be 3.5 to 6.7 micrograms per serving. The data collection is expected to be completed by the end of the year.

“The scientific approach is being taken right now to get a real handle on the typical level people consume,” Winter said. “Before you do that, it's hard to say any population is at risk.”

Arsenic may be present in some other foods, but most crops don't readily take up much arsenic from the ground. Rice is different because it is grown in flooded conditions. In an anaerobic environment, arsenic changes into a form that is easier for plants to absorb.

Richvale: Monday, 28 January, 8:00 am - 12:00, Evangelical Church, 5219 Church St., Richvale

Yuba City: Monday, 28 January, 1:00 pm - 5:00 pm, Veterans Hall, 1425 Veterans Memorial Circle, Yuba City

Colusa: Tuesday, 5 February, 8:00 am - 12:00, Colusa Industrial Properties Conference Room, 100 Sunrise Boulevard, Colusa

Glenn: Tuesday, 5 February, 1:00 pm - 5:00 pm, Glenn Pheasant Hall, 1522 Highway 45, south of Glenn

Program coming soon.