Michael J. Brewer

Approaches and Incentives to Implement Integrated Pest Management that Addresses Regional and Environmental Issues

Agricultural, environmental, and social and policy interests have influenced integrated pest management (IPM) from its inception. The first 50 years of IPM paid special attention to field-based management and market-driven decision making. Concurrently, IPM strategies became available that were best applied both within and beyond the bounds of individual fields and that also provided environmental benefits. This generated an incentives dilemma for farmers: selecting IPM activities for individual fields on the basis of market-based economics versus selecting IPM activities best applied regionally that have longer-term benefits, including environmental benefits, that accrue to the broader community as well as the farmer. Over the past several decades, public-supported incentives, such as financial incentives available to farmers from conservation programs for farms, have begun to be employed to encourage use of conservation techniques, including strategies with IPM relevance. Combining private investments with public support may effectively address the incentives dilemma when advanced IPM strategies are used regionally and provide public goods such as those benefiting resource conservation. This review focuses on adaptation of IPM to these broader issues, on transitions of IPM from primarily individual field-based decision making to coordinated community decision making, and on the form of partnerships needed to gain long-lasting regional and environmental benefits.

Relationship of soybean aphid (Hemiptera: Aphididae) to soybean plant nutrients, landscape structure, and natural enemies.

ABSTRACT In the north central United States, populations of the exotic soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), are highly variable across space, complicating effective aphid management. In this study we examined relationships of plant nutrients, landscape structure, and natural enemies with soybean aphid abundance across Iowa, Michigan, Minnesota, and Wisconsin, representing the range of conditions where soybean aphid outbreaks have occurred since its introduction. We sampled soybean aphid and its natural enemies, quantified vegetation land cover and measured soybean nutrients (potassium [K] and nitrogen [N]) in 26 soybean sites in 2005 and 2006. Multiple regression models found that aphid abundance was negatively associated with leaf K content in 2005, whereas it was negatively associated with habitat diversity (Simpsons index) and positively associated with leaf N content in 2006. These variables accounted for 25 and 27% of aphid variability in 2005 and 2006, respectively, suggesting that other sources of variability are also important. In addition, K content of soybean plants decreased with increasing prevalence of corn-soybean cropland in 2005, suggesting that landscapes that have a high intensification of agriculture (as indexed by increasing corn and soybean) are more likely to have higher aphid numbers. Soybean aphid natural enemies, 26 species of predators and parasitoids, was positively related to aphid abundance; however, enemy-to-aphid abundance ratios were inversely related to aphid density, suggesting that soybean aphids are able to escape control by resident natural enemies. Overall, soybean aphid abundance was most associated with soybean leaf chemistry and landscape heterogeneity. Agronomic options that can ameliorate K deficiency and maintaining heterogeneity in the landscape may reduce aphid risk.

Sugarcane Aphid (Hemiptera: Aphididae): Host Range and Sorghum Resistance Including Cross-Resistance From Greenbug Sources

ABSTRACT The graminous host range and sources of sorghum [Sorghum bicolor (L.) Moench.] plant resistance, including cross-resistance from greenbug, Schizaphis graminum (Rondani), were studied for the newly emerging sugarcane aphid, Melanaphis sacchari (Zehntner), in greenhouse no-choice experiments and field evaluations. The sugarcane aphid could not survive on field corn, Zea mays (L.), Teff grass, Eragrostis tef (Zucc.), proso millet, Panicum miliaceum L., barley, Hordeum vulgare L., and rye, Secale cereale L. Only sorghum genotypes served as hosts including Johnsongrass, Sorghum halepense (L.), a highly suitable noncrop host that generates high numbers of sugarcane aphid and maintains moderate phenotypic injury. The greenbug-resistant parental line RTx2783 that is resistant to greenbug biotypes C and E was resistant to sugarcane aphid in both greenhouse and field tests, while PI 55607 greenbug resistant to biotypes B, C, and E was highly susceptible. PI 55610 that is greenbug resistant to biotypes B, C, and E maintained moderate resistance to the sugarcane aphid, while greenbug-resistant PI 264453 was highly susceptible to sugarcane aphid. Two lines and two hybrids from the Texas A&M breeding program B11070, B11070, AB11055-WF1-CS1/RTx436, and AB11055-WF1-CS1/RTx437 were highly resistant to sugarcane aphid, as were parental types SC110, SC170, and South African lines Ent62/SADC, (Macia/TAM428)-LL9, (SV1*Sima/IS23250)-LG15. Tam428, a parental line that previously showed moderate resistance in South Africa and India, also showed moderate resistance in these evaluations. Overall, 9 of 20 parental sorghum entries tested for phenotypic damage in the field resulted in good resistance to the sugarcane aphid and should be utilized in breeding programs that develop agronomically acceptable sorghums for the southern regions of the United States.

Sugarcane Aphid (Hemiptera: Aphididae): A New Pest on Sorghum in North America

In 2013, the sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), a new invasive pest of sorghum species in North America, was confirmed on sorghum in 4 states and 38 counties in the United States. In 2015, the aphid was reported on sorghum in 17 states and over 400 counties as well as all sorghum-producing regions in Mexico. Ability to overwinter on living annual and perennial hosts in southern sorghum-producing areas and wind-aided movement of alate aphids appear to be the main factors in its impressive geographic spread in North America. Morphological characteristics of the sugarcane aphid include dark tarsi, cornicles, and antennae, allowing easy differentiation from other aphids on the crop. Sugarcane aphid damages sorghum by removing sap and covering plants with honeydew, causing general plant decline and yield loss. Honeydew and sooty mold can disrupt harvesting. The aphid’s high reproductive rate on susceptible sorghum hybrids has resulted in reports of yield loss ranging from 10% to greater than 50%. In response, a combination of research-based data and field observations has supported development of state extension identification, scouting, and treatment guides that aid in initiating insecticide applications to prevent yield losses. Highly efficacious insecticides have been identified and when complemented by weekly scouting and use of thresholds, economic loss by sugarcane aphid can be minimized. Some commercial sorghum hybrids are partially resistant to the aphid, and plant breeders have identified other lines with sugarcane aphid resistance. A very diverse community of predators and parasitoids of sugarcane aphid has been identified, and their value to limit sugarcane aphid population growth is under investigation.

Habitat Affinity of Resident Natural Enemies of the Invasive Aphis glycines (Hemiptera: Aphididae), on Soybean, with Comments on Biological Control

ABSTRACT We integrated a natural enemy survey of the broader landscape into a more traditional survey for Aphis glycines Matsumura (Hemiptera: Aphididae), parasitoids and predatory flies on soybean using A. glycines-infested soybean, Glycine max (L.) Merr., placed in cropped and noncropped plant systems to complement visual field observations. Across three sites and 5 yr, 18 parasitoids and predatory flies in total (Hymenoptera: Aphelinidae [two species] and Bracondae [seven species], Diptera: Cecidomyiidae [one species], Syrphidae [seven species], Chamaemyiidae [one species]) were detected, with significant variability in recoveries detected across plant system treatments and strong contrasts in habitat affinity detected among species. Lysiphlebus testaceipes Cresson was the most frequently detected parasitoid, and no differences in abundance were detected in cropped (soybean, wheat [Triticum aestivum L.], corn [Zea mays L.], and alfalfa [Medicago sativa L.]) and noncropped (poplar [Populus euramericana (Dode) Guinier] and early successional vegetation) areas. In contrast, Binodoxys kellggensis Pike, Starý & Brewer had strong habitat affinity for poplar and early successional vegetation. The low recoveries seasonally and across habitats of Aphelinus asychis Walker, Aphelinus sp., and Aphidius colemoni Viereck make their suitability to A. glycines on soybean highly suspect. The widespread occurrence of many of the flies reflects their broad habitat affinity and host aphid ranges. The consistent low field observations of parasitism and predation suggest that resident parasitoids and predatory flies are unlikely to contribute substantially to A. glycines suppression, at least during the conventional time period early in the pest invasion when classical biological control activities are considered. For selected species that were relatively well represented across plant systems (i.e., L. testaceipes and Aphidoletes aphidimyza Rondani), conservation biological control efforts may be fruitful. The additional information gained from expanding the natural enemy survey into the broader landscape was essential in making these distinctions relevant to conservation biological control, while adding agroecosystem-specific information valuable to classical biological control.

Alfalfa Weevil (Coleoptera: Curculionidae) Larval Sampling: Comparison of Shake-Bucket and Sweep-Net Methods and Effect of Training

Abstract Two field-sampling methods, shake-bucket and sweep-net, were compared for use in monitoring alfalfa weevil, Hypera postica (Gyllenhal), larvae in alfalfa hay of the high plains and intermountain region of North America. In this region, alfalfa grows to sufficient height to use both methods before the more damaging late instars peak in abundance. Both methods also were compared with extracting larvae by using Berlese funnels in the laboratory. The shake-bucket method was more sensitive in detecting small larvae (first and second instars) than large larvae (third and fourth instars), and the sweep-net method detected a lower proportion of small larvae. The number of larvae collected with the shake-bucket method was strongly correlated with number of larvae recovered from Berlese funnels (total larval counts, R2 = 0.85). Correlation of the sweep-net samples with the Berlese extraction was also significant but less strong (R2 = 0.56). In addition, sampler instruction was evaluated to determine whether demonstration training affects performance of inexperienced samplers using the two field-sampling methods. Training did not significantly change sampler performance in using the shake-bucket but did increase the number of large larvae when using the sweep-net. In addition, less variability was associated with the shake-bucket sampling method than with the sweep-net method for samplers who only had access to written sampling instructions. Therefore, when estimation of small larval abundance is desired for economic decision-making and sampling is performed by people with little or infrequent sampling experience, such as growers, the shake-bucket method is the preferred field-sampling method in the high plains and intermountain region of North America. Sweep-net sampling is more variable than shake-bucket sampling, although demonstration training improves the usefulness of the sweep-net.

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

ABSTRACT 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 Cry1Fx×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.

Presence-Absence Sequential Sampling Plan for Northern Fowl Mite, Ornithonyssus sylviarum (Acari: Macronyssidae), on Caged-layer Hens

Abstract Caged-layer hens were scored as infested or uninfested by visual examination of the vent region, and the number of northern fowl mite, Ornithonyssus sylviarum (Canestrini & Fanzago), per hen was estimated. The proportion infested and average number of mites per hen were shown to have a highly significant, positive relationship (r = 0.936). Sampling among houses within a flock, and rows and sections within houses were analyzed to determine the reliability of sampling a representative portion of a flock. Low- and moderate-tolerance treatment thresholds, based on percentage of hens infested with mites, were developed from sampling 1 wk before and 1 wk after acaricide treatments determined necessary by the producer. These thresholds were used to compare a fixed (single) sampling plan, a curtailed procedure of the fixed sampling plan, and a sequential sampling plan based on a sequential probability ratio test, by sampling 174 hens (the maximum number needed for the single sampling plan). The sequential sampling plan required fewer hen examinations on average to reach a treatment decision than did the other plans, depending on the infestation tolerance limits. Using a low tolerance approach in which infestations below 15% are considered noneconomic (safe threshold) and infestations above 25% are considered economically important (action threshold), as few as 5 hens required examination to reach a treatment decision. Sequential sampling plan graphs are presented for 2 tolerance threshold scenarios (a 15% safe-threshold paired with a 25% action threshold and a 35% safe-threshold paired with a 45% action threshold). These sequential sampling plans using presence absence assessments should greatly facilitate monitoring and treatment decisions for this important pest.

Sugarcane Aphid Population Growth, Plant Injury, and Natural Enemies on Selected Grain Sorghum Hybrids in Texas and Louisiana

Abstract In response to the 2013 outbreak of sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), on sorghum, Sorghum bicolor (L.), in North America, experiments were conducted at three southern U.S. grain sorghum production locations (Corpus Christi, TX; Winnsboro, LA; Rosenberg, TX). The objectives were to authenticate yield decline on susceptible hybrids (2014 and 2015) and to measure aphid population growth and natural enemy prevalence on susceptible and resistant hybrids with similar genetic background (2014).Yield decline on susceptible hybrids (Tx 2752/Tx430 and DKS53-67) was more substantial when aphid population growth accelerated quickly and peaked above 300 aphids per leaf (50 to nearly 100% yield decline). Location and year variation in maximum aphid density and cumulative aphid-days was high, with doubling time values on the susceptible hybrids ranging between 3.9 and 7.9 d. On resistant Tx2752/Tx2783, leaf injury and yield decline were not seen or less severe than on its paired susceptibleTx2752/Tx430. Aphids declined onTx2752/Tx2783 after initial colony establishment (Corpus Christi) or took about 60% longer to double in population size when compared with Tx2572/Tx430 (Winnsboro). The predominant natural enemy taxa were aphelinid mummies (Hymenoptera: Aphelinidae), ladybird beetles (Coleoptera: Coccinellidae), and sryphid flies (Diptera: Syrphidae), and they were more prevalent during flowering than prior to flowering.They were generally responsive to changes in aphid density of both susceptible and resistant hybrids, but variability points to need for further study. In future research, full season observations should continue as well as more detailed study of potential compatibility of sorghum resistance and biological control.

Probing Behavior of Diuraphis noxia and Rhopalosiphum maidis (Homoptera: Aphididae) Affected by Barley Resistance to D. noxia and Plant Water Stress

Abstract Probing behavior of Diuraphis noxia (Mordvilko), Russian wheat aphid, and Rhopalosiphum maidis (Fitch), corn leaf aphid, was measured on barley lines resistant and susceptible to D. noxia grown under low and high soil moisture. R. maidis reproduces similarly on both barley lines. Probing behavior was interpreted from waveforms of an alternating current electrical penetration graph (AC EPG) system of the Oklahoma design during 6-h monitoring periods. Significant effects were observed, particularly the aphid species by barley line interaction. Averaging across moisture levels, D. noxia took longer to first enter sieve element phase when probing D. noxia-resistant ‘STARS-9301B’ (306 ± 19.9 min [mean ± SEM]) than when probing susceptible ‘Morex’ (180 ± 21.6 min). In contrast, R. maidis relatively quickly entered sieve element phase on the two barley lines (average of 132 ± 13.7 min), with no detectable difference between lines. When measuring the total duration of sieve element phases, the stylets of D. noxia were in contact with phloem sieve elements of STARS-9301B for a shorter period (27 ± 10 min) than with sieve elements of Morex (111 ± 21 min). In contrast, stylets of R. maidis were in contact with sieve elements of the two barley lines for similar time periods (average of 176 ± 15.8 min). Any mediating effect of soil moisture was slight, if at all measurable, using the AC EPG system, making any interpretation of probing behavior relative to previous observations of aphid population growth affected by plant water stress untenable. In contrast, monitoring probing behavior was beneficial in assessing how plant resistance may affect aphid species differently. The differences in probing behaviors between the two aphids fed barley resistant and susceptible to D. noxia corresponded well with previous observations that D. noxia population growth was lower on D. noxia-resistant barley than on susceptible barley, while R. maidis population growth was similar on the two barley lines.