Quantifying the Contribution of Seed Blended Refugia in Field Corn to Helicoverpa zea (Lepidoptera: Noctuidae) Populations.

Helicoverpa zea (Boddie), a pest of cotton that also occurs in field corn, is commonly controlled through the use of foliar-applied insecticides or transgenic crops expressing Bacillus thuringiensis (Berliner) (Bt) genes. To minimize the risk of Bt resistance in pest populations, refuge systems have been implemented for sustainable agroecosystem management. Historically, structured refuge compliance among growers has been low, leading to the commercialization of seed blended refugia. To test the viability of seed blended refugia in southern U.S. field corn, field studies were conducted in Mississippi and Georgia during 2016, 2017, and 2018 growing seasons. To quantify adult H. zea emergence from structured (non-Bt corn) and seed blended refuge options, emergence traps were utilized. Kernel damage among seed blended refuge and structured refuge corn ears were recorded and compared. The timing of moth emergence was recorded. When compared to a structured refuge, H. zea adult moth emergence from seed blended refugia did not significantly differ. Kernel damage of non-Bt plants in the seed blended treatments was not significantly different than non-Bt plants in the structured refuge treatments. Moth emergence timing was not significantly delayed between the structured refuge and seed blended refuge treatments. Results of this study suggest that a seed blended refuge may provide an effective insecticide resistance management alternative for H. zea in areas where structured refuge compliance is low.

Influence of Soil Moisture Zones on Rice Water Weevil (Coleoptera: Curculionidae) Populations in Furrow Irrigated Rice.

Water conservation is an important factor for production of rice in the United States because of declining aquifer levels, but little research has been done to evaluate insect management in rice systems integrating water conservation practices. Rice water weevil, Lissorhoptrus oryzophilus Kuschel, is an important insect pest of rice in the U.S. Rice water weevil is a semiaquatic species that relies on flooded conditions to complete larval development, so water conservation practices are likely to impact their pest status. The study was conducted across the Mississippi River alluvial floodplain to compare rice water weevil population densities in different zones of a furrow irrigated rice field to a conventionally flooded rice field. All locations were sampled at 3, 4, and 5 wk after the initial irrigation. Larval densities were greatest in the lower end of furrow irrigated fields and in the adjacent flooded rice field compared with the upper and middle sections that did not hold standing water when averaged across three sample dates. Also, rice water weevil densities were greater during week five than week three. In terms of rice yields, the top third of furrow irrigated rice fields, the section that remained mostly dry, produced lower rough rice yields than all other sections and the flooded field. These results suggest that rice water weevil populations can be lower in a furrow irrigated rice system. As a result, more research is needed to determine whether a spatial management plan can be developed based on soil moisture zones in furrow irrigated rice.

Evaluation of Flood Removal in Combination with Insecticide Seed Treatment for Rice Water Weevil (Coleoptera: Curculionidae) Larval Management in Rice.

An experiment was conducted at the Delta Research and Extension Center in Stoneville, MS during 2017 and 2018 to determine whether removal of the flood is an economical method of control for rice water weevil, Lissorhoptrus oryzophilus Kuschel. This experiment compared a continuous flood production system to draining a rice field completely and reestablishing a flood for the remainder of the growing season. In addition, two insecticide seed treatments, thiamethoxam and chlorantraniliprole, were compared with an untreated control within each system. Rice water weevil densities were measured prior to draining at 3 wk after flood and again after the flood was reestablished in drained plots. Rice water weevil densities were greater in 2017 than 2018. Chlorantraniliprole at the predrainage and postdrainage sample timing reduced larval numbers compared with the untreated control. The plots where water was removed until soil cracking then re-flooded had significantly lower weevil populations than plots that were continuously flooded during 2018 only. Draining of plots resulted in lower yields in 2018, but not in 2017. Additionally, both of the insecticide seed treatments resulted in greater yields and economic returns than the untreated control. Draining of flooded rice when rice water weevil larvae were present did not provide a consistent benefit, and may result in yield and economic penalties. Insecticide seed treatments consistently provided greater yield benefits in flooded rice. Based on these results, draining of flooded rice is not recommended to manage rice water weevil and insecticide seed treatments should be used to minimize economic losses.

Evaluation of Current Tarnished Plant Bug (Hemiptera: Miridae) Thresholds in Transgenic MON 88702 Cotton Expressing the Bt Cry51Aa2.834_16 Trait.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important pest of cotton in many areas of the southern United States. An experiment was conducted at two locations in Mississippi during 2016 and 2017 to evaluate action thresholds for tarnished plant bug on a novel Bacillus thuringiensis cotton that expresses the Cry51Aa2.834_16 toxin. Treatments included the current action threshold, a 2× threshold, and treatments where insecticides were only applied during the early season (preflower) or only during late season (during flowering) based on the current action thresholds. These were compared to an untreated control and a weekly insecticide use regime that received weekly insecticide sprays. All treatments were imposed on both Bt Cry1Aa2.834_16 cotton and a nontraited cotton. The Bt Cry1Aa2.834_16 trait reduced the number of tarnished plant bugs and injury, and improved yields compared to nontraited cotton. For all spray treatments except the weekly insecticide use regime, yields were greater for the Bt Cry51Aa2.834_16 cotton than the nontraited cotton. In terms of thresholds, Bt Cry1Aa2.834_16 cotton sprayed based on current action thresholds resulted in similar yields to the weekly insecticide use regime of both cotton types. In contrast, the 2× threshold resulted in lower yields than the current threshold for both cotton types. Though thresholds intermediate to the currently recommended action threshold and the 2× threshold were not tested, these data suggest that currently recommended action thresholds appear appropriate for Bt Cry51Aa2.834_16 cotton. These results suggest that this trait will be an important component of current IPM programs in cotton where tarnished plant bug is an important pest.