Effects of Nitrogen Fertilization on Potato Leafhopper (Hemiptera: Cicadellidae) and Maple Spider Mite (Acari: Tetranychidae) on Nursery-Grown Maples.

Although leaf nitrogen (N) has been shown to increase the suitability of hosts to herbivorous arthropods, the responses of these pests to N fertilization on susceptible and resistant host plants are not well characterized. This study determined how different rates of N fertilization affected injury caused by the potato leafhopper (Empoasca fabae Harris) and the abundance of maple spider mite (Oligonychus aceris (Shimer)) on 'Red Sunset' red maple (Acer rubrum) and 'Autumn Blaze' Freeman maple (Acer×freemanii) during two years in Indiana. N fertilization increased leaf N concentration in both maple cultivars, albeit to a lesser extent during the second year of the study. Overall, Red Sunset maples were more susceptible to E. fabae injury than Autumn Blaze, whereas Autumn Blaze maples supported higher populations of O. aceris. Differences in populations of O. aceris were attributed to differences between communities of stigmaeid and phytoseiid mites on each cultivar. Injury caused by E. fabae increased with N fertilization in a dose-dependent manner in both cultivars. Although N fertilization increased the abundance of O. aceris on both maple cultivars, there was no difference between the 20 and 40 g rates. We suggest the capacity of N fertilization to increase O. aceris on maples could be limited at higher trophic levels by the community of predatory mites.

Effects of pesticide application on arthropod pests of nursery-grown maples.

Insecticides used against potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), have been reported to cause problems with maple spider mite, Oligonychus aceris (Shimer) (Acarina: Tetranychidae), on nursery-grown 'Red Sunset' red maple and 'Autumn Blaze' Freeman maple. To test this, we conducted two experiments on field-grown trees in nurseries. In the first, the effects of early-season pesticide applications were examined during 2009. The second experiment was conducted in 2010 to compare effects of using threshold levels of one, three, or six leafhoppers per branch to time applications. Pesticide applications reduced abundance and damage by leafhoppers in both cultivars, but increased populations of O. aceris on Autumn Blaze during 2009. In contrast, on Red Sunset, populations of O. aceris did not increase after insecticide applications. In 2010, insecticide applications did not increase abundance of O. aceris on Autumn Blaze because use of treatment thresholds to manage leafhoppers greatly reduced numbers of trees requiring treatment for leafhoppers. Two phytoseiid mites, Neoseiulus fallacis (Garman) and Typhlodromus caudiglans (Schuster), and one stigmaeid, Zetzellia mali (Ewing), were identified as the principal predators of O. aceris on maple leaves. Insecticide applications had no significant effects on the total abundance of predatory mites on either Red Sunset or Autumn Blaze maples in 2009 or 2010. However, populations of predator Z. mali were higher during both years on Red Sunset than on Autumn Blaze. These results suggest that both early-season pesticide use and cultivar can affect the likelihood of secondary outbreaks of spider mites on maples.

Factors influencing the abundance of pests in production fields and rates of interception of Dracaena marginata imported from Costa Rica.

Importation of live nursery plants, like Dracaena marginata Lamoureux (Ruscaceae), can provide a significant pathway for the entry of foliar pests from overseas into the United States. We studied the abundance of foliar pests of quarantine importance found on Costa Rican-grown D. marginata. These include five genera of leafhoppers (Heteroptera: Cicadellidae, Oncometopia, Caldweliola, Diestostema, Cypona, and Empoasca), Florida red scale (Heteroptera: Disapididae, Chrysomphalus aoinidum (L.)), katydids (Orthoptera: Tettigoniidae), and a snail (Succinea costarricana von Martens (Gastropoda, Stylommatophora, Succineidae)). In our first study, we examined the rationale behind size restrictions on Dracaena cuttings imported into the United States from Costa Rica. When comparing plant size, no differences were found in the abundance of quarantined pests on small (15-46 cm), medium (46-81 cm), and large (81-152 cm) propagules. In a second study, we estimated monthly abundances of pests in production plots for 1 yr to determine their relationship to rates of interception at U.S. ports. In any given month, < 6% of the marketable shoots standing in the field were infested with at least one quarantine pest. There was no relationship between the average monthly frequencies of pest detection in the field and in U.S. inspection ports. Pest detections increased during the 1 mo when average monthly shipments were abnormally high. Our data suggest that off-shore postprocessing efforts to remove pest-infested material from the market stream need to be adjusted to accommodate sharp increases in the volume of shipped plants.

Reducing insecticide volume and nontarget effects of ambrosia beetle management in nurseries.

Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) are increasingly important pests of nursery-grown trees because of the arrival of several invasive species. Ambrosia beetles bore into young trees and inoculate them with ambrosia fungus, which interferes with vascular transport resulting in limb or tree death. In spring, when beetles are active, growers make frequent applications of pyrethroid insecticides to susceptible tree species to deter beetles from boring into trees. Applications often are made with airblast sprayers that forcefully release insecticide mist that billows through nursery beds. Our objective was to compare the environmental, nontarget, and economic effects of airblast sprayer applications to applications made with a new dual-nozzle spray wand that makes targeted applications only to tree trunks where beetles attack. Through replicated experiments at commercial nurseries, we found that 5 times more insecticide was released by airblast sprayers than the manual spray wand. The extra insecticide from airblast applications landed on tree canopies, between rows, and left the nursery beds as drift. As a consequence of not spraying tree canopies, 50% more natural enemies and 50% fewer spider mites were captured in nursery beds treated with the manual spray wand than beds treated with the airblast sprayer. Manual applications require 12 times more labor than airblast applications. However, increased need for expensive miticide applications may make manual applications an economically feasible strategy for integrated pest management (IPM) of ambrosia beetles in nurseries.

Lessons From a 10-yr Invasive Species Webinar Program: Emerald Ash Borer University.

Information about invasive species needs to be spread rapidly across a wide geographic area following an invasion. However, in-person events can be time-consuming and costly for the participants, organizers, and presenters. Online programming like webinars can bridge this gap, but there is limited published data on how best to run these programs. We report on a 10-yr webinar program, Emerald Ash Borer University, and offer suggestions for improving their effectiveness as a communication tool. Webinar participants viewed the webinars positively and undertook recommended management actions. In addition, most of our survey respondents extended the reach of this program by widely sharing the information from the webinars. Posting the webinars on popular streaming platforms greatly extended their reach long after the live viewing event. Despite their longevity, viewers of recorded videos watched them differently than those viewing live events. We suggest modifying the format of future webinar presentations to accommodate these differences to improve information transfer.

Potential of suction traps as a monitoring tool for Aphis glycines (Hemiptera: Aphididae) in soybean fields.

The current study evaluated the potential of using counts of winged adults captured in suction traps to forecast the local abundance of soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in soybean, Glycine max (L.) Merr., fields. The abundance of aphids was evaluated weekly by sampling plants in four to 11 soybean fields and recording the number of aphids in suction traps between 2006 and 2008 in four counties in Indiana and Illinois. Fields in each county were located within 10 km of their respective suction trap, which allowed us to evaluate the relation between aphid abundance on soybean plants and in suction traps at the county level. Migrant soybean aphids caught in suction traps exhibited distinct seasonal trends each year: in 2006, trapped migrants consisted predominantly of individuals dispersing from soybean to buckthorn (Rhamnus sp.); in 2007, in contrast, the majority of trapped migrants were apparently individuals dispersing among soybean fields. The cumulative number of aphids captured in suction traps was positively related to aphid densities on soybean plants. However, the utility of suction traps as a monitoring tool may be limited by the variation in temporal patterns observed in suction traps and on soybean plants each year, and the spatial variation in aphid abundance among soybean fields within a county.

Excretion of non-metabolized insecticides in honeydew of striped pine scale.

Honeydew production is a characteristic of soft scales and other hemipteran insects. Honeydew has the capacity to alter the ecology of predators and parasitoids because it is used as a food resource and can contain insecticidal proteins from hemipteran host plants. We examined honeydew excreted by the striped pine scale (Hemiptera: Coccidae), Toumeyella pini (King), after feeding on pine trees treated with systemic insecticides to determine whether they could eliminate insecticidal compounds in honeydew. Imidacloprid and spirotetramat were applied at labeled rates to soil or foliage. Water sensitive paper was used to measure honeydew production and liquid chromatography coupled to mass spectrometry (LC-MS) to analyze excreted insecticide concentrations. Foliar and soil applications of imidacloprid caused a 25-fold reduction honeydew produced by scales six days after treatment (DAT). In contrast, spirotetramat treatments did not affect honeydew production. Parent compounds of both insecticides were detected in honeydew. However, on imidacloprid treated plants, these compounds were detected at similar concentrations in honeydew collected at 4 DAT from soil and foliar treatments. Imidacloprid was only detected from soil treatments at 8 DAT. Similarly, the spirotetramat parent compound was found 4 DAT after soil and foliar treatments, but only at 8 DAT in foliar treatments. At this time the concentration of spirotetramat in honeydew was six-fold higher than at 4 DAT. We conclude that striped pine scales excrete insecticides in honeydew even when the toxicant greatly reduces honeydew production. Honeydew excretion is thus a mechanism of bioaccumulation and has the potential to harm honeydew-feeding organisms.

Control of bagworms (Lepidoptera: Psychidae) using contact and soil-applied systemic insecticides.

The current study evaluated the effect of different classes of insecticides against bagworms (Lepidoptera: Psychidae) on arborvitae by using a laboratory bioassay that allowed us to simultaneously evaluate the feeding rate, growth, and mortality of larvae. Soil application of the systemic insecticides dinotefuran and (to a lesser extent) chlothianidin increased larval mortality and reduced the feeding rate and growth of larvae, up to 50 d posttreatment. The effectiveness of systemic insecticides against bagworms makes them well suited to control bagworms on tall trees heavily infested in the upper canopy. Chlorantranilipole and indoxacarb were as effective in controlling bagworms as other contact insecticides commercially available (spinosad and bifenthrin). Chlorantraniliprole had a residual effect 10 d posttreatment and may therefore provide an effective tool to protect the foliage of arborvitae against bagworms over a sustained period.

Effects of production practices on the abundance of quarantine pests in Dracaena marginata in Costa Rican production fields.

To mitigate risks of invasive pests, international nursery exporters may soon be expected to participate in clean stock programs that reduce the probability of shipping crops that contain pests of quarantine significance. We worked with Costa Rican producers of Dracaena marginata Lam. (Ruscaceae) to identify critical pests, as well as the field conditions and production practices that could be explored for lowering pest abundance in a clean stock program. We sampled the abundance of leafhopper and katydid eggs, armored scales, and snails on leaves using a 10- by 10-m grid in a total of 34 production plots located in two distinct growing regions during the rainy and dry seasons of 2006. Growers were surveyed to determine the production practices in each field. Populations of leafhoppers and snails increased during the rainy season, whereas armored scale populations reached higher densities in the dry season. Fertilizer applications were associated with a greater abundance of leafhoppers, the keystone pests in the system. In contrast, abundances of armored scales and katydids were somewhat lower in fertilized fields. Insecticide applications targeting leafhoppers succeeded in reducing their populations, but secondary outbreaks of armored scales and katydids were observed. Increased frequency of herbicide application was associated with lower populations of leafhoppers with no significant effects on the other herbivores. Although effects of specific production practices in a given plot are confounded, the effects of fertilizer, insecticide, and herbicide use on leafhoppers are consistent with those predicted by literature on this pest. For this reason, the 10- by 10-m sampling grid is sensitive enough for use in controlled studies that evaluate effects of specific practices on pest abundance. As such, it is likely to be a useful tool for developing a clean stock program for D. marginata in Costa Rica.

Effects of pesticide applications and cultural controls on efficacy of control for adult Japanese beetles (Coleoptera: Scarabaeidae) on roses.

Cultural and chemical controls were evaluated to determine their ability to deter feeding by Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae), on floribunda type roses, Rosa 'Acadia Sunrise'. Roses were arranged in field plots and exposed to resident adult beetle populations. Cultural controls were designed to block the feeding-induced aggregation response by manually removing beetles and/ or damaged blooms from rose plants. Azadirachtin, carbaryl, and imidacloprid were evaluated in field and laboratory trials. In no-choice laboratory assays, foliar applications of azadirachtin caused low rates of morbidity to adult beetles and were unable to deter feeding. Foliar-applied carbaryl and soil-applied imidacloprid caused high rates of morbidity and reduced feeding injury. In the field, foliar sprays of azadirachtin and carbaryl, deterred feeding on foliage under low beetle pressure (maximum of 29% defoliation in untreated controls), when applied weekly after first beetle flight or every 2 wk after 5% injury was reached. A single foliar application of these materials at the 5% injury level did not significantly reduce peak defoliation. Soil applications of imidacloprid also deterred foliar feeding in the field. Blooms were more difficult to protect with both foliar- and soil-applied insecticides with only weekly application of foliar insecticides providing significant reductions in bloom injury. Removing beetles and/or blooms provided marginally greater reductions in leaf and flower injury. This suggests that blocking the feeding-induced aggregation response of Japanese beetles can provide only modest levels of control in roses where both flowers and feeding-induced volatiles recruit beetles to plants.

Growth of Larval Agrilus planipennis (Coleoptera: Buprestidae) and Fitness of Tetrastichus planipennisi (Hymenoptera: Eulophidae) in Blue Ash (Fraxinus quadrangulata) and Green Ash (F. pennsylvanica).

Emerald ash borer (Agrilus planipennis Fairmaire) is an invasive primary pest of North American ash (Fraxinus spp.) trees. Blue ash (F. quadrangulata) is less susceptible to emerald ash borer infestations in the forest than other species of North American ash. Whereas other studies have examined adult host preferences, we compared the capacity of emerald ash borer larvae reared from emerald ash borer eggs in the field and in the laboratory to survive and grow in blue ash and the more susceptible green ash (F. pennsylvanica). Emerald ash borer larval survivorship was the same on both ash species. Mortality due to wound periderm formation was only observed in living field grown trees, but was low (<4%) in both green and blue ash. No difference in larval mortality in the absence of natural enemies suggests that both green and blue ash can support the development of emerald ash borer. Larvae reared from eggs on blue ash were smaller than on green ash growing in the field and also in bolts that were infested under laboratory conditions. In a laboratory study, parasitism rates of confined Tetrastichus planipennisi were similar on emerald ash borer larvae reared in blue and green ash bolts, as were fitness measures of the parasitoid including brood size, sex ratio, and adult female size. Thus, we postulate that emerald ash borer larvae infesting blue ash could support populations of T. planipennisi and serve as a potential reservoir for this introduced natural enemy after most of the other native ash trees have been killed.

Behavioral responses of a leaf beetle to injury-related changes in its salicaceous host.

Adults of the leaf beetle Plagiodera versicolora Laich, avoided previously injured shoots of Salix alba 'Tristis' in favor of nearby uninjured ones. The response was rapid and persisted for five days of study. During brief periods of observation, the vast majority of beetles engaged in behaviors other than locomotion such as feeding and resting. Furthermore, the proportions of beetles walking were similar on injured and uninjured shoots. It appears that under these experimental conditions previous injury did not greatly increase searching behavior of the beetles. Leaves on previously injured shoots received less subsequent herbivory than uninjured ones. Findings of these experiments are consistent with patterns of herbivory observed in the field and known reproductive responses of beetles to diets of injured leaves. These results provide new information toward understanding relatively low levels of herbivory on individual willow leaves associated with the feeding of P. versicolora.

Public tolerance to defoliation and flower distortion in a public horticulture garden.

Surveys of visitor and grower perception of live potted plant quality were conducted in various locations in a large public display garden. Canna lily, Canna x generalis L.H.Bailey, was used to examine effects of defoliation by Japanese beetle, Popillia japonica Newman, on public perception. Chrysanthemums, Chrysanthemum x morifolium Ramat., were used to identify visitor and grower tolerance to flower distortion caused by western flower thrips, Frankliniella occidentalis (Pergande), on single and multiple flowered plants. On average, the maximum amount of defoliation or flower distortion tolerated by any respondent was low (< or = 10% for canna and < or = 25% for chrysanthemum). The level of acceptable injury was influenced by factors intrinsic to both the respondents and the plants themselves. Tolerance to injury was negatively associated with the risk aversion of the respondents. Visitors were less tolerant of injury on plants they considered for purchase than those that they would view at the garden. Similarly, grower tolerance was lower than that of visitors because producing substandard plants could put their professional reputation at risk. Factors that distracted visitor attention (e.g., presence of flowers and higher levels of background injury) increased their tolerance to plant injury. Visitors tolerated greater levels of flower distortion on multiple flowering chrysanthemum than on those with single flowers. We suggest that tolerance to insect pests can be increased by designing plantings that distract viewers from injured plant parts.

Effects of pesticide applications on the euonymus scale (Homoptera: Diaspididae) and its parasitoid, Encarsia citrina (Hymenoptera: Aphelinidae).

Novel biorational insecticides are rapidly replacing more toxic, broad-spectrum compounds to control pests of ornamental plants. These new formulations are widely regarded as safe, effective, and environmentally sound with minimal impact on nontarget organisms. We tested several biorational and traditional insecticides for their ability to control euonymus scale, Unaspis euonymi (Comstock), and their potential impacts on the aphelinid parasitoid, Encarsia citrina (Crawford). Soil-applied acephate and foliar-applied pyriproxyfen exhibited superior control of euonymus scale, but also reduced numbers of surviving E. citrina. Imidacloprid failed to control euonymus scale and decreased parasitism by E. citrina. Thus, the potential impact of a pesticide on biological control is not necessarily predicted by its potential longevity, mode of delivery, or its toxicity to the target pest. Finding the best fit of a compound into an integrated pest management program requires a consideration of all these factors and direct study of effects on the natural enemies of pests.

Effects of weed cover composition on insect pest and natural enemy abundance in a field of Dracaena marginata (Asparagales: Asparagaceae) in Costa Rica.

Weeds and their influence on pest and natural enemy populations were studied on a commercial ornamental farm during 2009 in the Atlantic Zone of Costa Rica. A baseline survey of the entire production plot was conducted in February, along a 5 by 5 m grid to characterize and map initial weed communities of plants, cicadellids, katydids, and armored scales. In total, 50 plant species from 21 families were found. Seven weed treatments were established to determine how weed manipulations would affect communities of our targeted pests and natural enemies. These treatments were selected based on reported effects of specific weed cover on herbivorous insects and natural enemies, or by their use by growers as a cover crop. Treatments ranged from weed-free to being completely covered with endemic species of weeds. Although some weed treatments changed pest abundances, responses differed among arthropod pests, with the strongest effects observed for Caldwelliola and Empoasca leafhoppers. Removal of all weeds increased the abundance of Empoasca, whereas leaving mostly cyperacaeous weeds increased the abundance of Caldwelliola. Weed manipulations had no effect on the abundance of katydid and scale populations. No weed treatment reduced the abundance of all three of the target pests. Differential responses of the two leafhopper species to the same weed treatments support hypotheses, suggesting that noncrop plants can alter the abundance of pests through their effects on arthropod host finding and acceptance, as well as their impacts on natural enemies.

Ground beetle (Coleoptera: Carabidae) phenology, diversity, and response to weed cover in a turfgrass ecosystem.

Despite being fragmented and highly disturbed habitats, urban turfgrass ecosystems harbor a surprising diversity of arthropods. The suitability of turf as arthropod habitat, however, likely depends on the extent and types of pesticides and fertilizers used. For example, moderate levels of weed cover in low-input lawns may provide alternative food resources. We conducted a 2-yr field study to: 1) characterize the ground beetle (Carabidae) species assemblage in turfgrass, and 2) assess the direct and indirect effects of lawn management on carabid communities. Weed cover and beetle activity were compared among four lawn management programs: 1) consumer/garden center, 2) integrated pest management (IPM), 3) natural organic, and 4) no-input control. Nearly 5,000 carabid beetles across 17 species were collected with the predator Cyclotrachelus sodalis LeConte numerically dominating the trap catch (87% and 45% of individuals in 2005 and 2006, respectively). Populations of C. sodalis underwent a distinct peak in activity during the third week of June, whereas omnivorous and granivorous species tended to occur at far lower levels and were less variable over the season. We found no evidence for direct effects of lawn management on carabid species diversity; however, we detected an indirect effect mediated by variation in weed cover. Seed-feeding species were positively correlated with turf weeds early in 2006, whereas strictly predaceous species were not. Thus, turf management programs that lead to changes in plant species composition (i.e., herbicide regimes) may indirectly shape epigeal arthropod communities more strongly than the direct effects of insecticide use.

Impact of developmental maturity of soybean on the seasonal abundance of soybean aphid (Hemiptera: Aphididae).

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), alternates between a primary overwintering host (buckthorn, Rhamnus sp.) and a secondary summer host (soybean, Glycine max). Selection of soybean cultivars with different maturity groups may provide growers with a management tool for A. glycines, either directly through its effect on summer populations that cause economic damage or indirectly through its effect on the production of migrants that disperse to the primary host in fall. This study investigated the abundance and seasonality of A. glycines on soybean cultivars with different maturity rates in central Indiana. The abscission of soybean foliage occurred earlier for early maturing than late maturing cultivars, but no other consistent difference in development or yield was detected among the cultivars tested in this study. The abundance of aphids did not vary consistently among cultivars when soybean was most susceptible to economic damage. A laboratory assay evaluating the larviposition preference of A. glycines alate females, combined with a 7-yr survey documenting the colonization of buckthorn by winged aphids, indicated that the production of gynoparae on soybean began in mid-September and continued until leaf abscission. The abundance of aphids during this period was higher on late maturing cultivars than on early maturing cultivars in both 2006 and 2008, whereas no significant effect was detected in 2007. Altogether, these results suggest that planting early maturing soybean cultivars has little effect on damage by aphids on the current season crop but may reduce the number of fall migrants to the primary host.