Texas Cotton, Sorghum: Insecticidal Virus Products – What are the Facts?

    Bollworm, cotton square. Photo: Aaron Cato, University of Arkansas

    The arsenal of insecticides and acaricides that we have to select from for controlling arthropod pests is extremely important. Our arsenal may be limited due to cost of the product, which pesticide class will be effective, pests developing resistance, and the impact of a pesticide on beneficial populations or possible flaring of other pests. Therefore, we are always looking for new pesticides to add to our arsenal. 

    Toward the end of our growing season this year there was talk of a new insecticide for control of corn earworm/headworm/cotton bollworm. The active ingredient in this product is the nucleopolyhedrovirus (NPV) that is being used in Australia. What is interesting is that this “new insecticide” was studied as early as 1960’s and extensively during the 70’s and 80’s as the nuclear polyhedrosis virus.

    And, it was first registered in 1975 by EPA and marketed as Elcar, Biotrol VHZand Viron/H for Heliothis zea control in beans, corn, lettuce, peanuts, sorghum, soybeans, strawberry, tomato, and cotton. (Yes, I am dating myself). Registration for all of these old products has been cancelled.

    Now new products of the same NPV are being marketed as Heligen, Helicovex, and Gemstar. Are these new products any different from the older products? The virus itself is the same, but how the product is formulated or processed may or may not be different. So, what facts are available about NPV and these products.

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    Numerous NPVs have been identified for different lepidopteran insects, but each NPV is specific to a particular insect host or narrow range of hosts.These above NPV products are specific to larval stages of Helicoverpa (aka corn earworm, cotton bollworm, tomato fruitworm, soybean podworm, and sorghum headworm) and Heliothis virescens (tobacco budworm).

    There is an NPV marketed as Fawligen that is specific to Spodopteralarvae (fall armyworm and beet armyworm). Another NPV product (Loopex) is specific to the cabbage looper, Trichoplusia ni. These few examples of NPVs will not infect other insects or arthropods, including pests and beneficial predators and parasites.

    Figure 1. Old world cotton bollworm, Helicoverpa armigera, cadaver from NPV infection. Photo: O.P. Sharma, Bugwood.org

    As a simple illustration of how the virus works, a larva feeds on NPV treated plants where the virus infects the cells of the gut lining and begins to replicate throughout other cells in the larva. These infected cells rupture causing the larva to die. Viral particles are released from the larval cadaver onto the host leaves where healthy larvae can become infected when eating on the plant.

    Figure 2. Top, Dead Beet armyworm from NPV infection. Photo: David Nance, USDA-ARS, Bugwood.org

    Larval infection and mortality are dependent on the amount of NPV consumed and the larval size at infection. The infection rate of the target pest to the NPV in larvae is age-dependent. As with any biological insecticide, it may take a few days to a week for larvae to die.

    Often times dying larvae will climb to the top of the plant.  One great virtue of NPV insecticides is that they target a very narrow pest range, have no direct effect on beneficial insects, and offer little disruption to the arthropod complex in the field. These biological insecticides could be an alternative control method when the target pest has developed resistance to other available insecticides.

    However, with any product for controlling a pest there is a potential with increased exposure for the pest to develop resistance to the product over time, even NPV. For example, velvetbean caterpillars developed resistance following multiple generation exposure to NPV.

    We do not have any current data on the effectiveness of NPV product applications for control of the above listed pest species with field crops in the Texas High Plains. There was a trial this past summer conducted by Dr. Katelyn Kesheimer, former Extension agent–IPM (Lubbock, Crosby counties), with Heligen for control of sorghum headworm.

    At the time of application, the headworm population was very low, below economic threshold, which prevented any measurable results of the effectiveness for control of headworms in sorghum. However, she occasionally found diseased dead larvae when scouting the plots.

    Since we do not have any definitive results, we (Texas A&M AgriLife Extension) are hesitant to suggest the use of these products, but that does not mean that the products could not provide effective control under the right conditions.

    If you are interested in trying any of the NPV products see the table in the Source URL below for facts about the products and general guidelines to help obtain optimum results.

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