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In the southern plains of the United States, winter-adapted canola (Brassica napus L.) is a recently introduced annual oilseed crop that has rapidly increased in hectares during the past 10 yr. Winter canola fields are infested annually with populations of Brevicoryne brassicae (L.) and Lipaphis erysimi (Kaltenbach), and these Brassica specialists are known to sequester plant volatiles from host plants, producing a chemical defense system against predators. Myzus persicae (Sulzer) is also common in winter canola fields, but as a generalist herbivore, does not sequester plant compounds. These three aphid species are expected to affect predator survival and development in very different ways. We conducted laboratory studies to 1) determine whether Hippodamia convergens (Guérin-Méneville) and Chrysoperla carnea (Stephens) larvae demonstrate feeding preferences among winter canola aphids and 2) describe the suitability of these prey species. Predators demonstrated no significant preference among prey, and each aphid species was suitable for predator survival to the adult stage. However, prey species significantly affected development times and adult weights of each predator species. Overall, predator development was delayed and surviving adults weighed less when provided with L. erysimi or B. brassicae, which sequestered high levels of indole glucosinolates from their host plants. Our results indicate that although common winter canola aphids were suitable prey for H. convergens and C. carnea, qualitative differences in nutritional suitability exist between Brassica-specialist aphids and the generalist M. persicae. These differences appear to be influenced by levels of sequestered plant compounds that are toxic to aphid predators. [ABSTRACT FROM AUTHOR]

Generalist natural enemies play an important role in controlling soybean aphid, Aphis glycines (Hemiptera: Aphididae), in North America. Several sampling methods are used to monitor natural enemy populations in soybean, but there has been little work investigating their relative bias, precision, and efficiency. We compare five sampling methods: quadrats, whole-plant counts, sweep-netting, walking transects, and yellow sticky cards to determine the most practical methods for sampling the three most prominent species, which included Harmonia axyridis (Pallas), Coccinella septempunctata L. (Coleoptera: Coccinellidae), and Orius insidiosus (Say) (Hemiptera: Anthocoridae). We show an important time by sampling method interaction indicated by diverging community similarities within and between sampling methods as the growing season progressed. Similarly, correlations between sampling methods for the three most abundant species over multiple time periods indicated differences in relative bias between sampling methods and suggests that bias is not consistent throughout the growing season, particularly for sticky cards and whole-plant samples. Furthermore, we show that sticky cards produce strongly biased capture rates relative to the other four sampling methods. Precision and efficiency differed between sampling methods and sticky cards produced the most precise (but highly biased) results for adult natural enemies, while walking transects and whole-plant counts were the most efficient methods for detecting coccinellids and O. insidiosus, respectively. Based on bias, precision, and efficiency considerations, the most practical sampling methods for monitoring in soybean include walking transects for coccinellid detection and whole-plant counts for detection of small predators like O. insidiosus. Sweep-netting and quadrat samples are also useful for some applications, when efficiency is not paramount. [ABSTRACT FROM AUTHOR]

The soybean aphid ( Aphis glycines Matsumura) is a threat to soybean production in the Midwestern United States. Varieties containing the Rag1 soybean aphid resistance gene have been released with limited success in reducing aphid populations. Furthermore, virulent biotypes occur within North America and challenge the durability of single-gene resistance. Pyramiding resistance genes has the potential to improve aphid population suppression and increase resistance gene durability. Our goal was to determine if a pyramid could provide improved aphid population suppression across a wide range of environments.Weconducted a small-plot field experiment across seven states and three years. We compared soybean near-isolines for the Rag1 or Rag2 gene, and a pyramid line containing both genes for their ability to decrease aphid pressure and protect yield compared with a susceptible line. These lines were evaluated both with and without a neonicitinoid seed treatment. All aphid-resistant lines significantly decreased aphid pressure at all locations but one. The pyramid line experienced lower aphid pressure than both single-gene lines at eight of 23 location-years. Soybean aphids significantly reduced soybean yield for the susceptible line by 14% and for both single-gene lines by 5%; however, no significant yield decrease was observed for the pyramid line. The neonicitinoid seed treatment reduced plant exposure to aphids across all soybean lines, but did not provide significant yield protection for any of the lines. These results demonstrate that pyramiding resistance genes can provide sufficient and consistent yield protection from soybean aphid in North America. [ABSTRACT FROM AUTHOR]

Panicle caterpillars comprise an economically important insect pest complex of sorghum throughout the Great Plains of the United States, particularly in Kansas, Oklahoma, and Texas. The sorghum panicle caterpillar complex consists of larvae of two polyphagous lepidopteran species: the corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). Sampling for panicle caterpillars in sorghum fields is usually accomplished by the beat bucket sampling technique with a fixed sample size of 30 beat bucket samples of one sorghum panicle each per 16.2 ha of field. We used Wald's sequential probability ratio test for a negative binomial distribution to develop a sequential sampling plan for panicle caterpillars. In total, 115 sorghum fields were sampled in Kansas, Oklahoma, and Texas from June to August 2010. Panicle caterpillars had an aggregated distribution of counts confirmed by Pearson's chi-square statistic for lack of fit to the negative binomial distribution for each sampled field. A sequential sampling plan was developed using a high threshold (an economic threshold) of 0.5 caterpillars per sorghum panicle, a low threshold (a safe level) of 0.20 caterpillars per panicle, and fixed error rates (α = 0.10 and β = 0.05). At caterpillar densities >0.45 and <0.12 per panicle, the average number of panicles inspected to make a decision was less than the current recommendation of 30. In a 2013 validation test of 25 fields, the expected number of samples taken from average sample number curve was in close agreement with the number of samples required using the sequential plan ( r2 = 0.93), and all fields were correctly classified when compared with a fixed sample size result. The plan improved upon current sampling recommendations for panicle caterpillars in sorghum because at known acceptable fixed error rates fewer samples were required when caterpillars are scarce or abundant, whereas more samples were required to make decisions with the same acceptable error rates when densities were near the economic thresholds. [ABSTRACT FROM AUTHOR]

In general, Armadillidium vulgare (Latreille) are considered nonpests of soybean [Ghjcine max (L.) Merrill], but changes in soil conservation practices have shifted the pest status of this organism from an opportunistic to a perennial, early-season pest in parts of central Kansas. As a result, soybean producers that rotate with corn (Zea mays L.) under conservation tillage practices have resorted to removing excess corn residue by using controlled burns. In a 2-yr field study (2009 -2010), we demonstrated that residue removal in burned compared with unburned plots (measured as previous crop residue weights) had minimal impact on numbers of live and dead A. vulgare, soybean seedling emergence, and isopod feeding damage over time. Specifically, removal of residue by burning did not result in higher emergence rates for soybean stands or less feeding damage by A. vulgare. In a separate study, we found that number of live A. vulgare and residue weights had no consistent relationship with seedling emergence or feeding damage. Furthermore, seedling emergence was not impacted by higher numbers of A. vulgare in unburned plots, indicating that emergence in this study may have been influenced by factors other than A. vulgare densities. These studies demonstrate that removing residue through controlled burning did not impact seedling emergence in presence of A. vulgare and that residue and feeding damage to seedlings did not consistently relate to A. vulgare densities. Other factors that may have influenced a relationship between residue and live isopod numbers, such as variable moisture levels, are discussed. [ABSTRACT FROM AUTHOR]

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), reached damaging levels in 2003 and 2005 in soybean, Glycine max (L.) Merrill, in most northern U.S. states and Canadian provinces, and it has become one of the most important pests of soybean throughout the North Central region. A common experimental protocol was adopted by participants in six states who provided data from 19 yield-loss experiments conducted over a 3-yr period. Population doubling times for field populations of soybean aphid averaged 6.8 d ± 0.8 d (mean ± SEM). The average economic threshold (ET) over all control costs, market values, and yield was 273 ± 38 (mean ± 95% confidence interval Id], range 111-567) aphids per plant. This ET provides a 7-d lead time before aphid populations are expected to exceed the economic injury level (EIL) of 674 ± 95 (mean ± 95% CI, range 275-1,399) aphids per plant. Peak aphid density in 18 of the 19 location-years occurred during soybean growth stages R3 (beginning pod formation) to R5 (full size pod) with a single data set having aphid populations peaking at R6 (full size green seed). The ET developed here is strongly supported through soybean growth stage R5. Setting an ET at lower aphid densities increases the risk to producers by treating an aphid population that is growing too slowly to exceed the EIL in 7 d, eliminates generalist predators, and exposes a larger portion of the soybean aphid population to selection by insecticides, which could lead to development of insecticide resistance. [ABSTRACT FROM AUTHOR]

The soybean aphid, Aphis glycines Matsumura, has a heteroecious, holocyclic life cycle. Soybean aphids overwinter as eggs, hatch in the spring, reproduce asexually, and undergo three or more generations on buckthorn, Rhamnus spp., before migrating to a secondary host such as soybean, Glycine max (L.) Merr. The ability of different soybean aphid life stages to survive low temperatures potentially experienced during fall or winter is not known. The objectives of this study were to determine the supercooling point (SCP) of various soybean aphid life stages and to determine the annual probability that winter temperatures within the North Central region of the United States would equal or fall below the mean SCP of soybean aphid eggs. Aphid eggs are considered the most cold-hardy stage; therefore, their SCP can be used as a conservative estimate for aphid overwintering mortality. In our study, eggs had the lowest mean SCP (approximately -34°C) among all life stages, whereas gynoparae and oviparae had the highest mean SCPs (approximately -15°C). During the winter, extreme low air temperatures are likely to reach or exceed the mean SCP of soybean aphid eggs in portions of northern Minnesota, northern Wisconsin, and the upper peninsula of Michigan. Thus, widespread successful overwintering in the northern United States and southern Canada is less likely than in Illinois, Indiana, Ohio, Iowa, southern Minnesota, southern Wisconsin, and the lower peninsula of Michigan. [ABSTRACT FROM AUTHOR]

Soybean aphid, Aphis glycines Matsumura, is now widely established in soybean, Glycine max L., production areas of the northern United States and southern Canada and is becoming an important economic pest. Temperature effect on soybean aphid fecundity and survivorship is not well understood. We determined the optimal temperature for soybean aphid growth and reproduction on soybean under controlled conditions. We constructed life tables for soybean aphid at 20, 25, 30, and 35 ° C with aphotoperiod of 16:8 (L:D) h. Population growth rates were greatest at 25 ° C. As temperature increased, net fecundity, gross fecundity, generation time, and life expectancy decreased. The pre-reproductive period did not differ between 20 and 30 ° C; however, at 30 ° C aphids required more degree-days (base 8.6 ° C) to develop. Nymphs exposed to 35 ° C did not complete development, and all individuals died within 11 d. Reproductive periods were significantly different at all temperatures, with aphids reproducing longer and producing more progeny at 20 and 25 ° C than at 30 or 35 ° C. Using a modification of the nonlinear Logan model, we estimated upper and optimal developmental thresholds to be 34.9 and 27.8 ° C, respectively. At 25 ° C, aphid populations doubled in 1.5 d; at 20 and 30 ° C, populations doubled in 1.9 d. [ABSTRACT FROM AUTHOR]