Judith Hough-Goldstein

Arthropod natural enemies of the Colorado potato beetle

Abstract Mites, phalangids, spiders and insects have been studied as potential biological control agents of the Colorado potato beetle, Leptinotarsa decemlineata (Say). Insects include lacewings (Neuroptera: Chrysopidae), predatory stink bugs (Hemiptera: Pentatomidae, subfamily Asopinae), parasitic flies (Diptera: Tachinidae), predatory beetles (Coleoptera: Coccinelidae, Cicinilidae, Staphylinidae and Carabidae) and parasitic and predatory Hymenoptera. Both augmentative release and conservation of natural enemies are likely to increase in importance in Colorado potato beetle management, as broad-spectrum insecticides are replaced by more selective materials.

Effects of Straw Mulch on Pest Insects, Predators, and Weeds in Watermelons and Potatoes

Abstract Physical and biotic effects of straw mulch applied at two different times to potatoes and watermelons were assessed in field trials over 2 yr. Plots with straw mulch generally had lower soil temperatures and higher soil moisture than control (weedy, no straw) plots. When straw was applied at planting weeds were suppressed, whereas straw applied after cultivation 4 wk after planting had less effect on weeds. In 2000, potatoes with straw at planting had fewer potato leafhoppers, Empoasca fabae (Harris) (and less associated plant damage) and more colonizing Colorado potato beetle, Leptinotarsa decemlineata (Say), adults than the other treatments. Subsequent Colorado potato beetle egg mass and larval numbers, however, were not higher in this treatment, possibly because of the higher numbers of predators in these plots as assessed by pitfall trapping. In 2001, there were no differences in numbers of colonizing potato leafhopper or Colorado potato beetle adults, but by midsummer there were more Colorado potato beetle larvae in the control plots than in the straw plots, again possibly due to differential predation. The few pests observed in the watermelon plots were not affected by the straw treatments. Potato yields were similar in all treatments, but melon yields were higher in plots with straw at planting (in which weeds were suppressed) in 2000. In 2001, when melons were planted earlier in the spring, melon plant biomass at 4 wk was lower in plots with straw at planting than in the other treatments, probably due to reduced soil temperatures. Thus, for potatoes, straw may be useful to control weeds and enhance predator numbers, but insect pests may still require control. In melons, straw should be used only if the crop is planted after the soil is sufficiently warm.

Ground-Dwelling and Foliar Arthropods in Four Cropping Systems

Abstract Four different corn, soybean, and wheat cropping systems were established in small replicated plots and simultaneously in larger (4-hectare) unreplicated fields. Each system was subject to distinct tillage practices, fertility programs, and methods of pest control, based on methods currently in use on farms in the Mid-Atlantic region of the United States. Ground-dwelling arthropods (mostly Carabidae and spiders) were sampled during the fourth and sixth growing season after the establishment of the plots, and foliar insects (pest and beneficial) and pest damage were sampled on corn in the sixth growing season. Overall, beneficial arthropod populations were lowest and corn pest insect populations (especially Western corn rootworms, Diabrotica virgifera virgifera LeConte) were highest in the simplest, most intensively managed continuous corn system, which had annual use of soil insecticides. Generally ground-dwelling species were higher in soybeans than in corn, and in no-till than in deep-tilled crops. Growers wishing to enhance populations of beneficial insects should consider predominantly no-till cropping systems with several different crops in the rotation and minimal insecticide use. For both ground and foliar sampling, patterns of abundance among systems and crops in the small replicated plots generally followed those observed in the large fields, but numbers of spiders and carabids collected per pitfall trap were generally much higher in the large fields.

Feeding and Oviposition Behavior of Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) and Its Predicted Effectiveness as a Biological Control Agent for Polygonum perfoliatum L. (Polygonales: Polygonaceae)

Abstract Feeding and oviposition on different parts of mile-a-minute weed, Polygonum perfoliatum L. (Polygonales: Polygonaceae), by Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae), a potential biological control agent for the weed, were studied in quarantine. An additional experiment was conducted to test the effects of different levels of simulated damage by R. latipes on P. perfoliatum growth, survival, and reproduction. Female weevils consumed more P. perfoliatum overall than males and selectively fed on capitula more than on ocreae or leaves, whereas males fed more on ocreae than on leaves or capitula. More eggs were also laid on capitula than on other plant parts. Female feeding preference is probably because of the high protein content of the capitula, because protein is required for continued egg production, whereas males may maximize their reproductive success by feeding low and close to P. perfoliatum stems to intercept females as they emerge from pupation in the soil and ascend the plants to feed. The feeding and oviposition preferences of female R. latipes for plant capitula suggest that host specificity tests for this species should be conducted with plants that are flowering. Damage that simulated the effect of R. latipes larval feeding caused plant mortality when it was initiated on small P. perfoliatum plants and reduced biomass and seed production when it was initiated on larger plants. Thus R. latipes could have a substantial impact on P. perfoliatum if the weevil is released into the weed’s introduced range in North America.

Podisus maculiventris (Hemiptera: Pentatomidae) Predation on Ladybird Beetles (Coleoptera: Coccinellidae)

Adult Podisus maculiventris (Say) consumed no adult ladybird beetles (Harmonia axyridis Pallas) and 30-35% of larval ladybird beetles in no-choice laboratory trials. Nymphal P. maculiventris appeared to be more agile than adults in petri dishes and attacked 65% of both larval and adult H. axyrides; however, they only killed and consumed 50% of larvae and 20% of adult ladybird beetles. Ladybird beetle larvae were aggressive and often escaped, whereas adult beetles were usually rejected by the nymphal predators, suggesting unpalatability. Overall, P. maculiventris took more than four times longer to capture ladybeetle larvae than to capture fall armyworms (Spodoptera frugiperda [J. E. Smith]). In nature, while some ladybird beetles are undoubtedly consumed by P. maculiventris, most probably escape predation, either by evasion or through lack of palatability.

Arthropod Communities on Native and Nonnative Early Successional Plants

ABSTRACT Early successional ruderal plants in North America include numerous native and nonnative species, and both are abundant in disturbed areas. The increasing presence of nonnative plants may negatively impact a critical component of food web function if these species support fewer or a less diverse arthropod fauna than the native plant species that they displace. We compared arthropod communities on six species of common early successional native plants and six species of nonnative plants, planted in replicated native and nonnative plots in a farm field. Samples were taken twice each year for 2 yr. In most arthropod samples, total biomass and abundance were substantially higher on the native plants than on the nonnative plants. Native plants produced as much as five times more total arthropod biomass and up to seven times more species per 100 g of dry leaf biomass than nonnative plants. Both herbivores and natural enemies (predators and parasitoids) predominated on native plants when analyzed separately. In addition, species richness was about three times greater on native than on nonnative plants, with 83 species of insects collected exclusively from native plants, and only eight species present only on nonnatives. These results support a growing body of evidence suggesting that nonnative plants support fewer arthropods than native plants, and therefore contribute to reduced food resources for higher trophic levels.

Biology, Rearing, and Preliminary Evaluation of Host Range of Two Potential Biological Control Agents for Mile-a-Minute Weed, Polygonum perfoliatum L.

Abstract Basic biology and rearing methods were determined for Timandra griseata Peterson (Lepidoptera: Geometridae) and Homorosoma chinensis Wagner (Coleoptera: Curculionidae), two potential biological control agents of mile-a-minute weed (Polygonum perfoliatum L., Polygonaceae). Both species also were tested for their ability to feed and develop on crop plants in the family Polygonaceae. T. griseata defoliated potted mile-a-minute weed, developing from egg to adult in ≈26 d. However, T. griseata also fed and developed on common buckwheat (Fagopyrum esculentum Moench) and tartary buckwheat (Fagopyrum tartaricum Gaertn), and accepted these species and mile-a-minute weed equally in choice tests. Thus, the host range of T. griseata appears to be too broad for it to be considered for release in the United States. Homorosoma chinensis had a relatively high reproductive rate and short generation time on potted mile-a-minute weed. Internal feeding by H. chinensis larvae caused mortality of entire stems. Adult weevils fed on foliage of common buckwheat and rhubarb (Rheum rhabarbarum L.) when given no choice during an 8-wk test period, but laid no eggs on these hosts. In the same test, an average of over 130 eggs per female was laid on mile-a-minute weed. Newly emerged H. chinensis adults strongly preferred mile-a-minute weed to buckwheat and rhubarb in a choice test, and neonate larvae placed on buckwheat and rhubarb all died within 24 h. Thus, H. chinensis may be host specific to mile-a-minute weed, but further testing must be conducted on other potential host plants before release in the United States can be recommended.

Species Richness and Phenology of Cerambycid Beetles in Urban Forest Fragments of Northern Delaware

ABSTRACT Cerambycid beetles are abundant and diverse in forests, but much about their host relationships and adult behavior remains unknown. Generic blends of synthetic pheromones were used as lures in traps, to assess the species richness, and phenology of cerambycids in forest fragments in northern Delaware. More than 15,000 cerambycid beetles of 69 species were trapped over 2yr. Activity periods were similar to those found in previous studies, but many species were active 1–3 wk earlier in 2012 than in 2013, probably owing to warmer spring temperatures that year. In 2012, the blends were tested with and without ethanol, a host plant volatile produced by stressed trees. Of cerambycid species trapped in sufficient numbers for statistical analysis, ethanol synergized pheromone trap catches for seven species, but had no effect on attraction to pheromone for six species. One species was attracted only by ethanol. The generic pheromone blend, especially when combined with ethanol, was an effective tool for assessing the species richness and adult phenology of many cerambycid species, including nocturnal, crepuscular, and cryptic species that are otherwise difficult to find.

Manipulation of Weed Communities to Enhance Ground-Dwelling Arthropod Populations in Herbicide-Resistant Field Corn

Abstract Herbicide treatments were used in glyphosate-resistant field corn, Zea mays L., to produce treatments with weeds growing for varying periods of time in a replicated field trial conducted in three different fields over 3 yr. Increased weediness increased the activity-density of Harpalus pensylvanicus (DeGeer) (Coleoptera: Carabidae), the most common carabid species collected in pitfall traps. Field crickets, Gryllus spp. (Orthoptera: Gryllidae), showed a similar response, with generally higher numbers caught in weedier plots. Other ground-dwelling arthropod species showed variable responses to weediness. Wolf spiders (Lycosidae) showed an apparent response to fresh organic matter and dead weed thatch after herbicide treatments in 2002. Although several arthropods common in the field plots ate second instar western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), when the rootworms were presented to them on filter paper in the laboratory, rootworms were not consumed when presented to potential predators under a thin layer of soil. Predation on exposed larvae placed in the field for 24 h did not differ by treatment, possibly because the major species that differed by treatment were primarily herbivorous or omnivorous. Corn yields were lower in the weedy check plots all 3 yr, but no significant reduction in yield occurred in treatments with weeds present for 21, 31, or 41 d after planting, or in plots treated with preemergence herbicide only.

Interactive effects of light environment and herbivory on growth and productivity of an invasive annual vine, Persicaria perfoliata

Plant populations often exist in spatially heterogeneous environments with varying light levels, which can affect plant growth directly through resource availability or indirectly by altering behavior or success of herbivores. The plant vigor hypothesis predicts that herbivores are more likely to attack vigorously growing plants than those that are suppressed, for example in more shaded conditions. Plant tolerance of herbivory can also vary under contrasting resource availability. Observations suggest that damage by Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae), introduced into the United States in 2004 as a biological control agent for mile-a-minute weed (Persicaria perfoliata [L.] H. Gross), is greater in the sun than in shade. We compared weevil densities and plant growth in paired plots in full sun or under shade cloth; a second experiment included insecticide-treated plots in sun and shade, to assess the ability of the plant to compensate for herbivore damage. Greater density of weevils and more node damage (indicating internal larval feeding) were found on P. perfoliata plants growing in sun than on those in shade. Nodes were 14% thicker in the sun, which may have provided better larval habitat. Biomass produced by plants without weevils in the sun was about twice that produced in any other treatment. Herbivory had a greater effect on plant growth in the high-light environment than in the shade, apparently because of movement into the sun and increased feeding there by the monophagous herbivore, R. latipes. Results support the plant vigor hypothesis and suggest that high weevil densities in the sunny habitats favored by P. perfoliata can suppress plant growth, negating the resource advantage to plants growing in the sun.