Evaluation of Foliar Insecticides for the Control of Western Bean Cutworm in Field Corn, 2016

The western bean cutworm (WBC) is an important pest of corn and dry beans. In addition to yield loss due to direct feeding on developing kernels in the ear, WBC infestation can also lead to secondary fungal infections. This study was conducted within the historic range of WBC in western Nebraska; however, it has undergone a rapid range expansion into the eastern Corn Belt within the last 16 years. This field trial was established to evaluate the efficacy of a single application of foliar insecticides against this pest to prevent feeding damage to non-Bt corn ears. The trial was located at the University of Nebraska-Lincoln’s Stumpf International Wheat Center in Perkins County, Nebraska, USA (40.856805° N, –101.701594° W). A RCB design with 10 treatments (including an untreated check) and 4 replications was used. Each plot was eight rows by 35 ft. The trial was planted on 13 May using a small plot research planter at 32,000 seeds/acre at an approximate depth of 1.4– 1.75 inch in 30 inch rows. The hybrid planted was DKC62-95 (Monsanto Company, St. Louis, MO) non-Bt with RR2 herbicide tolerance. The plots received irrigation, fertilization, and weed management inputs following standard agronomic practices for the region, with no insecticide applications other than the experimental treatments

Survival and Development of Striacosta albicosta (Smith) (Lepidoptera: Noctuidae) Immature Stages on Dry Beans, non-Bt, Cry1F, and Vip3A Maize

Striacosta albicosta is a crop pest that causes economic damage in the United States and Canada. Only maize and dry beans are shown to be suitable hosts, since larval development is incomplete on other hosts. The objective of this study was to describe the developmental parameters of immature stages of S. albicosta feeding on dry beans, non-Bt, Cry1F, and Vip3A maize. For Vip3A, mortality was 100% after 24 h. Larvae feeding on non-Bt maize had the highest larval survival (70.6%) compared to the other hosts. Maize expressing Cry1F had higher survival (31.3%) than dry beans (26.0%). Larvae feeding on dry beans had a significantly faster total development time (74.8 days), compared to 92.5 days for non-Bt and 96.2 days for Cry1F. All larvae developed through seven instars. Pupae from larvae that had fed on non-Bt maize were significantly heavier than pupae from other hosts. An understanding of S. albicosta immature development on various host plants is needed to improve recommendations for effective scouting, treatment timing, and economic thresholds. Differential development can result in an extended adult emergence period, and possibly result in assortative mating between Bt susceptible and resistant populations, which violates the assumption of random mating necessary for current resistance management strategies for Bt maize. Therefore, understanding the impact of host plant and transgenic traits on aspects of pest biology will aid in developing effective integrated pest management and insect resistance management strategies for this pest

Life-History Parameters of Striacosta albicosta (Lepidoptera: Noctuidae) Under Laboratory Conditions

Striacosta albicosta (Smith) is a key pest of maize and dry beans in North America. It has expanded its distribution from the western Great Plains of the United States to the Great Lakes region in the United States and Canada. There has been limited research on the baseline biological aspects of this insect under controlled conditions. The objective of this study was to detail the biological parameters of S. albicosta feeding on an artificial diet under laboratory conditions. Overall survival from neonate to adult at 26.6 ± 1°C was 36.72% and the total developmental time was approximately 110 d. Survival of the egg, larval, prepupal, and pupal stages were 75.71, 98.50, 51.78, and 95.10%, respectively. Average duration of the egg, larval, prepupal, and pupal stages was 4.64, 28.20, 41.50, and 25.91 d, respectively. During the larval stage, 92.50% of larvae developed through seven instars and the remaining through six instars. Larvae that developed through six and seven instars exhibited a mean growth ratio of 1.60 and 1.47, respectively; however, there was no difference in pupal weight. Eggs laid by field-mated moths showed a fertility of 75.71%, compared with 4.18% from laboratory-reared moths. These data suggest that S. albicosta develop primarily through seven instars and the most vulnerable developmental stage is the prepupa. Laboratory conditions strongly affected fertility success. Information presented here greatly expands our understanding of S. albicosta biology, which can be used to improve the efficiency of laboratory bioassays and management techniques for this critical crop pest

Bifenthrin Baseline Susceptibility and Evaluation of Simulated Aerial Applications in \u3ci\u3eStriacosta albicosta\u3c/i\u3e (Lepidoptera: Noctuidae)

Striacosta albicosta (Smith) is a maize pest that has recently expanded its geographical range into the eastern United States and southeastern Canada. Aerial application of pyrethroids, such as bifenthrin, has been a major practice adopted to manage this pest. Reports of field failure of pyrethroids have increased since 2013. Striacosta albicosta populations were collected in 2016 and 2017 from maize fields in Nebraska, Kansas, and Canada and screened with bifenthrin active ingredient in larval contact dose-response bioassays. Resistance ratios estimated were generally low in 2016 (1.04- to 1.32-fold) with the highest LC50 in North Platte, NE (66.10 ng/cm2) and lowest in Scottsbluff, NE (50.10 ng/cm2). In 2017, O’Neill, NE showed the highest LC50 (100.66 ng/cm2) and Delhi, Canada exhibited the lowest (6.33 ng/cm2), resulting in a resistance ratio variation of 6.02- to 15.90-fold. Implications of bifenthrin resistance levels were further investigated by aerial application simulations. Experiments were conducted with a spray chamber where representative S. albicosta populations were exposed to labeled rates of a commercial bifenthrin formulation. Experiments resulted in 100% mortality for all populations, instars, insecticide rates, and carrier volumes, suggesting that levels of resistance estimated for bifenthrin active ingredient did not seem to impact the efficacy of the correspondent commercial product under controlled conditions. Results obtained from this research indicate that control failures reported in Nebraska could be associated with factors other than insecticide resistance, such as issues with the application technique, environmental conditions during and/or after application, or the insect’s natural behavior. Data generated will assist future S. albicosta resistance management programs

Movement of \u3ci\u3eStriacosta albicosta\u3c/i\u3e (Smith) (Lepidoptera: Noctuidae) Larvae on Transgenic \u3ci\u3eBt\u3c/i\u3e and Non-\u3ci\u3eBt\u3c/i\u3e Maize

Exposure of lepidopteran pests to Bacillus thuringiensis (Bt) proteins has been shown to affect the behavior of larvae, including increased movement and avoidance of Bt-expressing plants or diet. Therefore, we hypothesized that the behavior of western bean cutworm, Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), an important pest of maize, could be affected when exposed to Bt plants. To test this hypothesis, we conducted a series of artificial arena and on-plant experiments to determine S. albicosta neonate behavior when exposed to Bt and non-Bt plant tissue. Video tracking experiments presented neonate larvae with the choice of Bt or non-Bt pollen in a Petri dish for 15 min while being video recorded for analysis with EthoVision software. This study showed an increase in mean velocity and total time spent moving for larvae in the presence of Cry1F vs. non-Bt when compared with Vip3A vs. non-Bt or Cry1F vs. Vip3A. However, there was no difference in total distance moved or time spent in the food zone for all scenarios. Maize tissue choice experiments allowed neonatal larvae the choice of feeding on Bt or non-Bt tassel or leaves for 9 h in Petri dish arenas. This experiment showed that larvae preferred tassel tissue over leaves but did not indicate that larvae could distinguish between Bt and non-Bt tissue. In contrast, on-plant experiments (including a whole plant neonate dispersal study under controlled conditions and an in-field silking behavior experiment) indicated that the presence of Cry1F and Vip3A Bt toxins increased plant abandonment, suggesting that larvae are able to detect and avoid Bt toxins. The discrepancy of these results is likely due to the on-plant studies providing more field-realistic environmental conditions and a longer duration of exposure to Bt toxins for the behavioral experiments. Our results represent the first steps in understanding the complex behavior of S. albicosta when exposed to Bt plants. A better understanding of the response of larvae when exposed to Bt traits can aid in the management of this pest, particularly for the design of resistance management strategies and refuge design

Biotic potential and reproductive parameters of Spodoptera dolichos (Lepidoptera: Noctuidae) in the laboratory

The biotic potential and reproductive parameters of Spodoptera dolichos (Fabricius, 1794) were evaluated under controlled conditions (25 ± 1°C, 70 ± 10% RH and 14 hour photophase). The longevity, pre-, post- and oviposition periods, fecundity, and fertility of 25 couples were evaluated. The longevity of females (12.9 days) was not significantly different than that of males (12.4 days). The mean durations of the pre-, post- and oviposition periods were 3.0, 0.4 and 10.4 days, respectively. The mean fecundity was 4,086.0 eggs per female and mean fertility was 3,557.8 larvae per female. On average, a female copulated 1.4 times. The biotic potential of S. dolichos was estimated at 7.138 x 1018 individuals/female/year. The net reproductive rate (Ro) was 1,711.98 times per generation and the mean generation time (T) was 56.19 days. The intrinsic rate of increase (rm) was 0.133, with a finite rate of increase (l) of 1.142 per day. These results are compared with other species from Spodoptera and their relevance for management strategies of S. dolichos

Bifenthrin Baseline Susceptibility and Evaluation of Simulated Aerial Applications in \u3ci\u3eStriacosta albicosta\u3c/i\u3e (Lepidoptera: Noctuidae)

Striacosta albicosta (Smith) is a maize pest that has recently expanded its geographical range into the eastern United States and southeastern Canada. Aerial application of pyrethroids, such as bifenthrin, has been a major practice adopted to manage this pest. Reports of field failure of pyrethroids have increased since 2013. Striacosta albicosta populations were collected in 2016 and 2017 from maize fields in Nebraska, Kansas, and Canada and screened with bifenthrin active ingredient in larval contact dose-response bioassays. Resistance ratios estimated were generally low in 2016 (1.04- to 1.32-fold) with the highest LC50 in North Platte, NE (66.10 ng/cm2) and lowest in Scottsbluff, NE (50.10 ng/cm2). In 2017, O’Neill, NE showed the highest LC50 (100.66 ng/cm2) and Delhi, Canada exhibited the lowest (6.33 ng/cm2), resulting in a resistance ratio variation of 6.02- to 15.90-fold. Implications of bifenthrin resistance levels were further investigated by aerial application simulations. Experiments were conducted with a spray chamber where representative S. albicosta populations were exposed to labeled rates of a commercial bifenthrin formulation. Experiments resulted in 100% mortality for all populations, instars, insecticide rates, and carrier volumes, suggesting that levels of resistance estimated for bifenthrin active ingredient did not seem to impact the efficacy of the correspondent commercial product under controlled conditions. Results obtained from this research indicate that control failures reported in Nebraska could be associated with factors other than insecticide resistance, such as issues with the application technique, environmental conditions during and/or after application, or the insect’s natural behavior. Data generated will assist future S. albicosta resistance management programs

Aspectos biológicos de Tiracola grandirena(Herrich-Schäffer, 1868) (Lepidoptera: Noctuidae) : uma lagarta polífaga

Estudou-se a biologia de Tiracola grandirena(Herrich-Schäffer, 1868) (Lepidoptera: Noctuidae: Hadeninae) em condições controladas de 25 ± 1 °C, 70 ± 10% UR e fotofase de 14 horas. Na fase larval foram estabelecidos três experimentos empregando 150 larvas cada. No primeiro, os insetos foram criados individualmente, com dieta artificial de Grenee, cujos dados foram utilizados para avaliar a duração e a sobrevivência das larvas, pupas e adultos. No segundo, as larvas foram criadas individualmente, alimentadas com folhas de 10 plantas de famílias diferentes avaliando-se a sobrevivência e duração larval (fase ativa). No terceiro, as larvas foram mantidas em um mesmo recipiente, variando-se a alimentação vegetal, três espécies a cada 48 horas, avaliando-se apenas a sobrevivência larval. No primeiro experimento a viabilidade de ovo, larva, pré-pupa e pupa foi de 91,93; 94,67; 32,39 e 43,48%, respectivamente. A duração média de ovo, larva, pré-pupa, pupa e adulto foi de 6,00; 25,26; 25,76; 21,35 e 12,67 dias, respectivamente. O prolongado período de pré-pupa indicou que, nas condições em que foi criada T. grandirena pode desenvolver diapausa larval (pré-pupal). Os resultados dos experimentos com diferentes plantas hospedeiras demonstraram que T. grandirena é polífaga ao nível específico, populacional e individual.We studied the biology of Tiracola grandirena(Herrich-Schäffer, 1868) (Lepidoptera: Noctuidae: Hadeninae) at 25 ± 1 °C, 70 ± 10% RH and 14 hours of photo phase. Three experiments, using 150 larvae each, were conducted for the larval stage. In the first, used to assess the duration and survival of all stages, insects were reared individually and fed an artificial diet (Grenee). In the second, individuals were also reared separately, but were fed leaves of 10 plants from different families. In the third, the larvae were not individualised, the food plants were rotated such as to provide three plant species every 48 hours. In the first experiment, the viability of the eggs, larvae, pupae and prepupae was 91.9, 94.7, 32.49 and 43.5%, respectively. The average duration of the egg, larvae, prepupae, pupae and adult were 6.0, 25.3, 25.7, 21.4 and 12.7 days, respectively. The prolonged prepupal period indicates that T. grandirena can develop larval (prepupal) diapause. The results of the experiments with different host plants showed that T. grandirena is polyphagous at species, population and individual level

Potencial reprodutivo de Spodoptera eridania (Stoll) (Lepidoptera: Noctuidae) em laboratório : efeito de múltiplos casais e do tamanho

Este estudo objetivou avaliar o efeito de confinar três casais em cada gaiola e o tamanho de adultos emergidos de pupas pequenas, medias e grandes (278,67 mg, 333,20 mg e 381,58 mg, respectivamente), sobre o potencial reprodutivo de S. eridania (Stoll, 1782), em condições controladas (25 ± 1 °C, 70% UR e 14 horas de fotofase). Avaliou-se a sobrevivência, o número de cópulas, fecundidade e fertilidade dos adultos. A sobrevivência não diferiu significativamente entre fêmeas provenientes de pupas de diferentes tamanhos, mas os machos oriundos de pupas grandes tiveram sobrevivência significativamente menor que os demais tamanhos. A fecundidade diferiu significativamente e correlacionou-se positivamente com o tamanho. O número de cópulas (espematóforos) e a fertilidade não variaram em função do peso pupal. Os resultados enfatizam a importância de indicar o número de cópulas e o tamanho dos insetos estudados para que comparações entre os parâmetros reprodutivos possam ser efetuadas.This study aimed to evaluate the effect of keeping three couples in the same cage, and the size of adults emerged from small, medium-sized and large pupae (278.67 mg; 333.20 mg and 381.58 mg, respectively), on the reproductive potential of S. eridania (Stoll, 1782) adults, under controlled conditions (25 ± 1 °C, 70% RH and 14 hour photophase). We evaluated the survival, number of copulations, fecundity and fertility of the adult females. The survival of females from these different pupal sizes did not differ statistically, but the survival of males from large pupae was statistically shorter than from small pupae. Fecundity differed significantly and correlated positively with size. The number of effective copulations (espematophores) and fertility did not vary significantly with pupal size. Our results emphasize the importance of indicating the number of copulations and the size of the insects when reproductive parameters are compared