Lepidoptera (Crambidae, Noctuidae, and Pyralidae) Injury to Corn Containing Single and Pyramided Bt Traits, and Blended or Block Refuge, in the Southern United States.

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae); corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae); southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae); sugarcane borer, Diatraea saccharalis F. (Lepidoptera: Crambidae); and lesser cornstalk borer, Elasmopalpus lignosellus Zeller (Lepidoptera: Pyralidae), are lepidopteran pests of corn, Zea mays L., in the southern United States. Blended refuge for transgenic plants expressing the insecticidal protein derivative from Bacillus thuringiensis (Bt) has recently been approved as an alternative resistance management strategy in the northern United States. We conducted a two-year study with 39 experiments across 12 states in the southern United States to evaluate plant injury from these five species of Lepidoptera to corn expressing Cry1F and Cry1Ab, as both single and pyramided traits, a pyramid of Cry1Ab×Vip3Aa20, and a pyramid of Cry1F×Cry1Ab plus non-Bt in a blended refuge. Leaf injury and kernel damage from corn earworm and fall armyworm, and stalking tunneling by southwestern corn borer, were similar in Cry1F×Cry1Ab plants compared with the Cry1F×Cry1Ab plus non-Bt blended refuge averaged across five-plant clusters. When measured on an individual plant basis, leaf injury, kernel damage, stalk tunneling (southwestern corn borer), and dead or injured plants (lesser cornstalk borer) were greater in the blended non-Bt refuge plants compared to Cry1F×Cry1Ab plants in the non-Bt and pyramided Cry1F×Cry1Ab blended refuge treatment. When non-Bt blended refuge plants were compared to a structured refuge of non-Bt plants, no significant difference was detected in leaf injury, kernel damage, or stalk tunneling (southwestern corn borer). Plant stands in the non-Bt and pyramided Cry1F×Cry1Ab blended refuge treatment had more stalk tunneling from sugarcane borer and plant death from lesser cornstalk borer compared to a pyramided Cry1F×Cry1Ab structured refuge treatment. Hybrid plants containing Cry1F×Cry1Ab within the pyramided Cry1F×Cry1Ab blended refuge treatment had significantly less kernel damage than non-Bt structured refuge treatments. Both single and pyramided Bt traits were effective against southwestern corn borer, sugarcane borer, and lesser cornstalk borer.

Effects of Japanese beetle (Coleoptera: Scarabaeidae) and silk clipping in field corn.

Japanese beetle (Popillia japonica Newman) is an emerging silk-feeding insect found in fields in the lower Corn Belt and Midsouthern United States. Studies were conducted in 2010 and 2011 to evaluate how silk clipping in corn affects pollination and yield parameters. Manually clipping silks once daily had modest effects on yield parameters. Sustained clipping by either manually clipping silks three times per day or by caging Japanese beetles onto ears affected total kernel weight if it occurred during early silking (R1 growth stage). Manually clipping silks three times per day for the first 5 d of silking affected the number of kernels per ear, total kernel weight, and the weight of individual kernels. Caged beetles fed on silks and, depending on the number of beetles caged per ear, reduced the number of kernels per ear. Caging eight beetles per ear significantly reduced total kernel weight compared with noninfested ears. Drought stress before anthesis appeared to magnify the impact of silk clipping by Japanese beetles. There was evidence of some compensation for reduced pollination by increasing the size of pollinated kernels within the ear. Our results showed that it requires sustained silk clipping during the first week of silking to have substantial impacts on pollination and yield parameters, at least under good growing conditions. Some states recommend treating for Japanese beetle when three Japanese beetles per ear are found, silks are clipped to < 13 mm, and pollination is < 50% complete, and that recommendation appears to be adequate.

Impacts of seeding rate on interactions between rice and rice water weevils.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most widely distributed and destructive early season insect pest of rice, Oryza sativa L., in the United States. Economic losses result primarily from feeding by the larval stage of this insect on the roots of flooded rice plants. Prior studies suggest that infestations of rice water weevil larvae are more severe at low plant densities. Moreover, because feeding by the rice water weevil reduces rice plant tillering, a process particularly important to yield at low seeding rates, infestations by weevil larvae may have a greater impact on rice yields when rice is seeded at low rates. In total, six experiments were conducted over a 3-yr period in Louisiana and Missouri to investigate the impacts of rice seeding rate on levels of infestations by, and yield losses from, the rice water weevil. An inverse relationship between seeding rate and densities of rice water weevil larvae and pupae on a per area basis was found in two of the six experiments. Furthermore, in two of the three experiments conducted with 'Bengal' (a susceptible cultivar) in Louisiana, percentages of yield loss were significantly higher at lower seeding rates than at higher seeding rates. Overall, these results indicate that rice sown at low rates is more vulnerable to infestation by rice water weevils and more susceptible to yield losses from weevil injury. The significance of these findings in light of recent trends toward the use of lower seeding rates in drill-seeded rice is discussed.

Efficacy of Cry1Ac:Cry1F proteins in cotton leaf tissue against fall armyworm, beet armyworm, and soybean looper (Lepidoptera: Noctuidae).

Cotton, Gossypium hirsutum L., plants expressing Cry1Ac and Cry1F insecticidal crystal proteins of Bacillus thuringiensis Berliner (Bt) were evaluated against selected lepidopteran pests including fall armyworm, Spodoptera frugiperda (J. E. Smith), beet armyworm, Spodoptera exigua (Hübner), and soybean looper, Pseudoplusia includens (Walker). Studies were conducted in a range of environments, challenging various cotton tissue types from several varieties containing a combination of Cry1Ac and Cry1F proteins. In fresh tissue bioassays of mature leaves and squares (flower buds) and in artificial field infestations of white flowers, plants containing Cry1Ac:Cry1F significantly reduced levels of damage (leaf defoliation, bract feeding, penetrated squares and bolls, and boll abscission) and induced significantly greater mortality (90-100%) of fall armyworm compared with that on non-Bt cotton plants. Plants containing Cry1Ac:Cry1F conferred high levels (100%) of soybean looper mortality and low levels (0.2%) of leaf defoliation compared with non-Bt cotton. Beet armyworm was relatively less sensitive to Cry1Ac:Cry1F cotton plants compared with fall armyworm and soybean looper. However, beet armyworm larval development was delayed 21 d after infestation (DAI), and ingestion of plant tissue was inhibited (14 and 21 DAI) on the Cry1Ac:Cry1F plants compared with that on non-Bt cotton plants. These results show Cry1Ac:Cry1F cotton varieties can be an effective component in a management program for these lepidopteran pest species. Differential susceptibility of fall armyworm, beet armyworm, and soybean looper larvae to Cry1Ac:Cry1F cotton reinforces the need to sample during plant development and respond with a foliar insecticide if local action thresholds are exceeded.

Evaluation of the potential role of glufosinate-tolerant rice in integrated pest management programs for rice water weevil (Coleoptera: Curculionidae).

The impact of a herbicide-tolerant rice, Oryza sativa L., variety was assessed for its resistance to rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), and its place in current integrated pest management (IPM) programs. Greenhouse experiments were conducted to evaluate the resistance of a glufosinate-tolerant rice variety and its glufosinate-susceptible parent line Bengal to the rice water weevil in the presence and absence of glufosinate applications. The LC50 dose-response and behavioral effects of glufosinate on adult rice water weevils also were studied. Field studies investigated the impacts of glufosinate-tolerant rice on rice water weevil management in the presence and absence of glufosinate under early and delayed flood conditions. Greenhouse studies demonstrated that in the absence of glufosinate, oviposition was 30% higher on the glufosinate-tolerant rice line than on Bengal rice or on glufosinate-tolerant line treated with recommended rates of commercially formulated glufosinate. Applications of glufosinate to glufosinate-tolerant rice resulted in a 20% reduction in rice water weevil larval densities compared with nontreated glufosinate-tolerant rice. The LC50 of glufosinate against adult rice water weevil was nearly 2 times the concentration recommended for application to glufosinate-tolerant rice. There was no difference in the amount of leaf area consumed by adult rice water weevils on glufosinate-treated and nontreated foliage. The absence of direct toxicity of glufosinate to rice water weevil at recommended glufosinate use rates and lack of behavioral effects suggest that the reduction in rice water weevil densities observed after glufosinate applications resulted from herbicide-induced plant resistance. Field experiments showed that neither rice variety nor herbicide use affected larval densities; however, delaying flood and applying insecticide effectively reduced numbers of rice water weevil larvae.