Protection of Rice from Invertebrate Pests, 2013


Project Leader

Larry D. Godfrey, extension entomologist, Dept. of Entomology and Nematology, UC Davis

This project focuses on the biology and management of key invertebrate pests of California rice. In 2013 the primary targets of research were rice water weevil (RWW) and tadpole shrimp. In addition, researchers examined the rice agroecosystem and the red-shouldered stinkbug as a potential insect pest. Scientists also continued research on rice variety response to RWW infestation. The goal of all this work is to refine and advance cost-effective integrated pest management practices that protect the rice agroecosystem.

RWW flight and biology

The 2013 RWW spring flight was unusually prolonged. Peaks in RWW flight were noted on April 10 and May 14, as well as April 26-30 and May 8-14. Some RWW were captured on 20 separate nights in 2013. The flight was low to moderate, with a total of 832 RWW captured—one-fifth the number captured in 2012 but more than twice the number from 2011.

RWW management

In 2013, studies of insecticidal management of RWW took place in aluminum ring plots, small field plots, and greenhouses to evaluate experimental insecticides and registered standards.

Ring plots are a cost-effective way to compare products and treatments. However, this method introduces some artificial aspects in testing. For instance, RWW adults are introduced into the rings in clutches to lay eggs and to start the infestation instead of more gradually. Seven different active ingredients were examined in 21 treatments. Eight different follow-up treatments were conducted in open-field plots.

Pyrethroid insecticides still show good activity on rice water weevil. Warrior® was effective in preflood, early post-flood, and 3-leaf applications. Protection of yield and control of RWW larvae was consistent in all studies.

The newly available Declare® performed equally well against RWW in the ring study in preflood and 3-leaf applications. Mustang® provided a lower level of RWW control than the other two pyrethroids. Mustang®, in particular, was weak in preflood application (not recommended for this product).

In recent years there have been complaints that in some cases pyrethroid insecticide applications have not adequately controlled rice water weevil. However, a laboratory analysis of field-collected RWW adults showed no evidence of resistance development.

Belay® was evaluated preflood, early post-flood, at 3-leaf, and the 5-6 leaf stage (as a “rescue” treatment). The preflood application was moderately effective but less so than the post-flood application. The early post-flood and 3-leaf applications were very effective. The rescue application showed good activity as well. This product was registered for use in 2014.

Coragen® (active ingredient rynaxypyr) from DuPont™ was applied preflood and post-flood in the ring study and at three rates in open-field plots. Preflood applications were effective; post-flood applications were not. Coragen® appears to be effective but slow to control RWW. This product is still in the experimental stage.

Agrichemical companies are emphasizing reduced risk, biorational, and biological insecticides. Microorganisms and byproducts from microorganisms can have insecticidal properties. If appropriate, microbe products can be applied directly to crops, the byproduct isolated and applied to crops, or some portion of the microbe can be inserted into plants to afford crop protection. A biological insecticide, Bacillus thringiensis galleriae, was tested again in greenhouse studies. It showed potential for RWW control. Registration of this product for agricultural crops is pending.

Variety susceptibility studies  

Host plant resistance for rice water weevil has been extensively studied with limited success. The “silver bullet”—a rice genotype that the insect will not damage—has not been found. Another approach to host-plant resistance is using it to provide partial control in an integrated program.

Examining commercial rice cultivars to see if there are any differences in the ability of key invertebrate pests to feed upon and damage these plants is one way to facilitate this goal. As new varieties are developed and production practices improve, rice plants are becoming more vigorous and higher yielding. This may influence pest interactions and rice plant response.

Two studies were conducted in 2013 to examine the response of commonly grown California rice cultivars to rice water weevil. Severity of infestation and yield loss upon infestation were documented. In a ring-plot study with introduced RWW adults, there were significantly more scarred plants in M-202 than an experimental line and L-206. S-102 had the lowest infestation, while L-206 consistently had the highest RWW infestation. In M-202 and the experimental line, the infestation was intermediate. However, M-202 was severely impacted by the infestation, with a calculated yield loss of 3,600 pounds/acre (64% of potential yield). The experimental line suffered a comparatively low yield loss at 500 pounds/acre (14% of potential yield).

Twelve rice varieties were compared in a similar study using a “natural” RWW infestation. This plot had a very low RWW infestation and thus no meaningful data were collected. Grain yields ranged from a high of 7,400 pounds/acre in M-206 to a low of 5,230 pounds/acre in M-205.

Another study examined weevil impacts on rice productivity with two varieties planted at four seeding rates. Observations suggest that M-206 may offer more resistance to RWW than M-202. Seeding rate influences this interaction. Data are still being analyzed. Grain yields from the open-field plots peaked at 8,630 pounds/acre for M-202 seeded at 150 pounds/acre.

Tadpole shrimp

Tadpole shrimp has emerged as a significant pest of rice in the last few years.

Tadpole shrimp eggs can lay dormant for 10 years and still hatch as soon as they are exposed to water.  Rice seeds that do not have a chance to germinate and root can be attacked by tadpole shrimp, adversely affecting stand establishment.

The use of copper sulfate or “bluestone” for tadpole shrimp control has dropped significantly. Growers have been relying on pyrethroid treatments, which are effective in the short-term but may not provide residual control. Thus, tadpole shrimp levels continue to build and alternative management methods are needed.

A field study was conducted in ring plots to evaluate registered and experimental products. Warrior®, with all application methods, provided excellent control. The experimental product Coragen® also showed excellent control. Belay® was effective with a post-flood application but less so when applied preflood. As with rice water weevil, the preflood method with Belay® is not conducive for effective tadpole shrimp control.

Nontarget studies

As new insecticides are being proposed for inclusion into rice pest management programs, the fit of these products into the overall rice agroecosystem needs to be evaluated. Specifically, the effects of insecticides on populations of aquatic nontarget invertebrates (both insects and related organisms) need to be determined, as this can impact mosquito populations arising from rice fields.

The preflood treatments of Warrior® and the experimental Coragen® in 2012 had low initial effects on populations of nontarget organisms (2013 data are still being evaluated). Conversely, the insecticides applied at the 3-leaf stage were very detrimental to these populations. Declare® had the most severe impacts on aquatic insects, with reductions of more than 75% for six of the first seven weeks after application. Comparable results were seen with Warrior®, although the reductions were not as severe. Belay® was “easier” on populations of aquatic insects. Declare® and Warrior® also had the most negative effects of the three insecticides on populations of other aquatic invertebrates at this timing. Warrior® applied in July for potential control of armyworms generally had low to moderate effects on nontarget organisms.

Pecky rice studied

Pecky rice is generally not a problem in California rice production. In recent years, however, rice kernel damage has been reported in some fields. The rice stinkbug commonly causes pecky rice in the South, but this pest species is not known to occur in California. Several agronomic and environmental factors can also cause grain malformations, but insect feeding is the most common cause.

In 2012, scientists searched for possible insect causes in one of the areas with pecky rice in 2011 and found a low level of red-shouldered stinkbug (RSSB). This is not an invasive or new insect in California. Studies in 2013 were conducted to determine its potential to damage rice. A colony of RSSB was raised in a laboratory at UC Davis for this research.


Red-shouldered stinkbug (above) was investigated in connection with reports of damaged or "pecky" rice kernels (below)

In the first study, RSSB adults were placed within a mesh cage that covered several rice plants. In the second study, individual panicles were infested with RSSB in small cages. Cages were left until grain maturity. Grain damage ranged from 2.8% to 5.4%. Milling yields and head-rice yields were not affected by RSSB. However, there was indication that RSSB has the potential to reduce rough rice grain yields. It remains to be determined how widespread this pest is, how much damage it is doing in grower fields, and whether it needs to be controlled.

Other invasive insects

Other recent invasive insects of concern to the rice industry include two stinkbug species that have been detected in the Central Valley.

The brown marmorated stinkbug was accidentally imported from Asia to North America in the late 1990s. Initially found in Pennsylvania, it is now found in 40 states. In California, this pest was first found in the Los Angeles basin. Reproducing populations have been found in the lower Sacramento Valley. It can cause damage to grapes, orchard crops, small fruits, ornamentals, vegetables, and field crops. 

The Bagrada bug is another invasive stinkbug infesting western Arizona and Southern California since 2008.  It has now moved up the coast to the Bay Area and is also in the Central Valley.  In desert agriculture, Bagrada bug is a pest of cole crops and other mustard family plants but reportedly also feeds on strawberries, melons, and members of the nightshade (potatoes, peppers), mallow (okra, cotton), legume, and grain (wheat, corn, sudangrass, millet) families.

The cereal leaf beetle invaded the Klamath Basin in 2013 and has the potential to damage rice. This species feeds on most grass plants. 

Research on these species will be conducted as soon as possible.

A recently invaded mosquito that can carry yellow fever was identified in Madera, Clovis, and San Mateo last summer. Besides yellow fever, the Aedes aegypti mosquito transmits dengue and several other viruses. Although the disease organisms are not in California, the presence of the vector is a concern.  It prefers to breed in containers, so it may not infest agricultural fields.