Daniel A. Potter

Insecticide resistance in the bed bug: a factor in the pest's sudden resurgence?

Abstract Infestations of the bed bug, Cimex lectularius L. (Heteroptera: Cimicidae), are increasing around the world at an alarming rate and have become a major public health concern. The evolution of insecticide resistance could be a primary factor in explaining this resurgence. Extremely high levels of resistance to two pyrethroid insecticides, deltamethrin and &lgr;-cyhalothrin, relative to a susceptible colony, were detected in populations collected from human dwellings in Kentucky and Ohio. Offspring of a cross between a resistant and susceptible colony had intermediate susceptibility. Evaluations of populations from across the United States indicate that resistance to pyrethroid insecticides is already widespread. Without the development of new tactics for bed bug management, further escalation of this public health problem should be expected.

Volatile compounds induced by herbivory act as aggregation kairomones for the Japanese beetle (Popillia japonica Newman)

The Japanese beetle is a polyphagous insect that typically aggregates on preferred host plants in the field. We studied the response of Japanese beetles to artificial damage, fresh feeding damage, and overnight feeding damage to test the hypothesis that beetles are attracted to feeding-induced volatiles. Crabapple leaves that had been damaged overnight by Japanese beetles or fall webworms attracted significantly more Japanese beetles than did undamaged leaves. Artificially damaged leaves or leaves freshly damaged by Japanese beetles, however, were not significantly more attractive than undamaged leaves. Leaves that had been damaged overnight by Japanese beetles or fall webworms produced a complex mixture of aliphatic compounds, phenylpropanoid-derived compounds, and terpenoids. In comparison, artificially damaged leaves or leaves with fresh Japanese beetle feeding damage generated a less complex blend of volatiles, mainly consisting of green-leaf odors. Feeding-induced odors may facilitate host location and/or mate finding by the Japanese beetle.

Nutritional quality of specific leaf tissues and selective feeding by a specialist leafminer

SummaryMany folivorous insects are selective feeders which consume specific leaf tissues. For specialist herbivores feeding on plants of overall low nutritional quality, selective feeding may allow consumption of a high quality resource. Selective feeding may also allow insects to avoid structural or allelochemical defenses. We examined the structure and chemistry of leaves of American holly, Ilexopaca Aiton, and the feeding site of its principal insect herbivore, the native holly leafminer, Phytomyza ilicicola Loew (Diptera: Agromyzidae), to test the hypothesis that the leafminer consumes tissues which are of greater nutritional quality than the leaf as a whole. Holly leaves have a continuous layer of palisade mesophyll, uninterrupted by fibers or vascular bundles. The leafminer feeds entirely within this layer. The palisade mesophyll contained 196 mg/g dry wt extractable protein, more than twice as much as the leaf as a whole, and 375 mg/g dry wt saponins, more than 9 times that of the leaf as a whole. The water content of the palisade mesophyll was 66% higher than that of the leaf as a whole. The palisade mesophyll is 3–4 cell layers thick in leaves grown in full sun, but only 2 layers thick in shaded leaves. Crystals, probably of calcium oxalate, are abundant in the abaxial cell layer. These may impose mechanical constraints on larval feeding in shade leaves, which are thinner than sun leaves. Selective feeding on the middle palisade mesophyll of sun leaves allows the leafminer to consume a resource which is lacking in mechanical barriers and is rich in protein and water, but which contains large amounts of saponins.

Lethal and Sublethal Effects of Bendiocarb, Halofenozide, and Imidacloprid on Harpalus pennsylvanicus (Coleoptera: Carabidae) Following Different Modes of Exposure in Turfgrass

Abstract Routes by which nontarget predatory insects can be exposed to turfgrass pesticides include topical, residual, and dietary exposure. We used each of these routes to evaluate potential lethal or sublethal effects of two novel turfgrass insecticides, imidacloprid and halofenozide, and a carbamate, bendiocarb, on survival, behavior, and fecundity of the ground beetle Harpalus pennsylvanicus DeGeer. Field-collected carabids were exposed to direct spray applications in turf plots, fed food contaminated by such applications, or exposed to irrigated or nonirrigated residues on turf cores. Halofenozide caused no apparent acute, adverse effects through topical, residual, or dietary exposure. Moreover, the viability of eggs laid by females fed halofenozide-treated food once, or continuously for 30 d, was not reduced. In contrast, topical or dietary exposure of carabids to bendiocarb inevitably was lethal. Exposure to imidacloprid by those routes caused high incidence of sublethal, neurotoxic effects including paralysis, impaired walking, and excessive grooming. Intoxicated beetles usually recovered within a few days in the laboratory, but in the field, they were shown to be highly vulnerable to predation by ants. One-time intoxication by imidacloprid did not reduce females’ fecundity or viability of eggs. There was no apparent behavioral avoidance of insecticide residues, or of insecticide-treated food. Carabids exposed to dry residues on turfgrass cores suffered high mortality from bendiocarb, and some intoxication from imidacloprid, but these effects were greatly reduced by posttreatment irrigation. Implications for predicting hazards of insecticides to beneficial invertebrates in turfgrass are discussed.

Hazards of Insecticides to the Bumble Bees Bombus impatiens (Hymenoptera: Apidae) Foraging on Flowering White Clover in Turf

Abstract Insecticides used on turf are sometimes applied to areas with flowering weeds that attract honey bees and native pollinators. We tested residual effects of such treatments on colony vitality and behavior of the bumble bees Bombus impatiens Cresson foraging on turf containing white clover, Trifolium repens L. Imidacloprid, a systemic chloronicotinyl used for preventive control of root-feeding grubs, was applied as granules, followed by irrigation, or sprayed as a wettable powder, with or without irrigation. Hives were confined on the plots in large field cages after residues had dried and colony vitality (i.e., numbers of brood, workers, and honey pots, and weights of queens, workers, and whole colonies with hives) was evaluated after 28–30 d. Workers’ foraging activity and defensive response to an aggressive stimulus also were evaluated. In another test, weedy turf was sprayed with chlorpyrifos, carbaryl, or cyfluthrin at labeled rates for surface-feeding pests. Bee colonies were confined on the plots after residues had dried, with effects on colony vitality evaluated after 14 d. Finally, foraging activity of wild bumble bees was monitored on open plots to determine if insecticide-treated areas were avoided. Imidacloprid granules, and imidacloprid sprays applied with posttreatment irrigation, had no effect on colony vitality or workers’ behavior, suggesting that such treatments pose little systemic or residual hazard to bumble bees. In contrast, exposure to dry nonirrigated residues of all of the aforementioned insecticides had severe impact on colony vitality. Foraging workers did not avoid insecticide-treated areas. Means by which turf managers can reduce hazards of insecticide applications to pollinators are discussed.

Carbohydrate reserves, radial growth, and mechanisms of resistance of oak trees to phloem-boring insects.

SummaryThe twolined chestnut borer, Agrilus bilineatus (Weber) (Coleoptera: Buprestidae), attacks oaks (Quercus spp.) that have been weakened by prior environmental or biotic stress. Our earlier work showed that trees with relatively low winter starch reserves are more likely to be attacked by A. bilineatus the following summer. We hypothesized that such trees may have less energy available for defense (Callus formation and allelo-chemical synthesis) in tissues wounded by borer larvae. However, wounding experiments showed little or no relationship between winter or summer carbohydrate reserves, callus formation, radial growth, or concentrations of tannins and phenolics in wounded or nonwounded phloem tissues. Trees with relatively low winter carbohydrate reserves were again found to be attractive to adult A. bilineatus, although not all low starch trees were attacked or successfully colonized by borers. There was a trend for carpenterworm larvae, Prinoxystus robiniae (Lepidoptera: Cossidae), a generalist bark and wood borer, to be more successful in establishing galleries on low starch trees. Carpenterworms gained significantly more weight when fed phloem from trees attractive to A. bilineatus. Oaks that attracted large numbers of A. bilineatus or that were successfully colonized by the borer produced significantly less callus than did non-attacked trees when experimentally wounded at about the time of Agrilus egg hatch. Callus formation may limit the establishment of small larvae that feed slowly in the cambial region. These results indicate that current theory regarding relationships between increased tree stress and decreased allocation of energy reserves to radial growth and defense against phloem borers may be an oversimplification. We suggest that tree growth and the defensive response of phloem tissues may be limited more by the rate of carbohydrate utilization or by changes in source-sink relationships than by storage levels. Callus formation and synthesis of allelochemicals in wounded phloem may be under the same control as cambial activation, which is mediated by plant growth regulators and can be influenced by environmental conditions.

Assessing Insecticide Hazard to Bumble Bees Foraging on Flowering Weeds in Treated Lawns

Maintaining bee-friendly habitats in cities and suburbs can help conserve the vital pollination services of declining bee populations. Despite label precautions not to apply them to blooming plants, neonicotinoids and other residual systemic insecticides may be applied for preventive control of lawn insect pests when spring-flowering weeds are present. Dietary exposure to neonicotinoids adversely affects bees, but the extent of hazard from field usage is controversial. We exposed colonies of the bumble bee Bombus impatiens to turf with blooming white clover that had been treated with clothianidin, a neonicotinoid, or with chlorantraniliprole, the first anthranilic diamide labeled for use on lawns. The sprays were applied at label rate and lightly irrigated. After residues had dried, colonies were confined to forage for six days, and then moved to a non-treated rural site to openly forage and develop. Colonies exposed to clothianidin-treated weedy turf had delayed weight gain and produced no new queens whereas those exposed to chlorantraniliprole-treated plots developed normally compared with controls. Neither bumble bees nor honey bees avoided foraging on treated white clover in open plots. Nectar from clover blooms directly contaminated by spray residues contained 171±44 ppb clothianidin. Notably, neither insecticide adversely impacted bee colonies confined on the treated turf after it had been mown to remove clover blooms present at the time of treatment, and new blooms had formed. Our results validate EPA label precautionary statements not to apply neonicotinoids to blooming nectar-producing plants if bees may visit the treatment area. Whatever systemic hazard through lawn weeds they may pose appears transitory, however, and direct hazard can be mitigated by adhering to label precautions, or if blooms inadvertently are contaminated, by mowing to remove them. Chlorantraniliprole usage on lawns appears non-hazardous to bumble bees.

Population regulation of the native holly leafminer, Phytomyza ilicicola Loew (Diptera: Agromyzidae), on American holly

SummaryThree sources of mortality, intraspecific competition, parasitism, and early leaf abscission, were investigated to determine their importance in regulating populations of the leafminer Phytomyza ilicicola Loew (Diptera: Agromyzidae) on cultivated American holly trees. Spatial aggregation of leafminers among leaves resulted in density-dependent mortality from interference and from intraspecific competition for nutritional resources. Pupal weight of survivors decreased significantly as within-leaf density increased. Within-tree parasitism of P. ilicicola by Opius striativentris (Hymenoptera: Braconidae) ranged from 3%–58%, but parasitism was independent of host density both for individual leaves and on a tree-wide spatial scale. The incidence of early leaf abscission was significantly higher for mined than for unmined leaves, with about 14% of the mined leaves abscising before the adult leafminers emerged. There was high mortality of both P. ilicicola and O. striativentris within fallen leaves. These results are discussed in relation to recent hypotheses concerning the role of competition, parasitism, and early leaf abscission in population regulation of leafminers.

Ant Predation on Eggs and Larvae of the Black Cutworm (Lepidoptera: Noctuidae) and Japanese Beetle (Coleoptera: Scarabaeidae) in Turfgrass

Abstract We studied ant predation on eggs and larvae of the black cutworm, Agrotis ipsilon (Hufnagel), and on eggs of the Japanese beetle, Popillia japonica Newman, on golf courses and lawns in central Kentucky. Lasius neoniger Emery accounted for >99% of the ant mounds on golf putting greens and collars. Although often regarded as a nuisance pest, L. neoniger preyed heavily upon A. ipsilon eggs on turfgrass cores implanted into putting greens, collars, fairways, and roughs. Predation on eggs was lower in fairways than in roughs, and in plots where ant populations were reduced by insecticides. When 1,600 individual 1st-instar cutworms were placed near L. neoniger nests on putting greens, 62% were attacked and killed upon their 1st encounter with the ants. Third- and 4th-instar cutworms generally fended off attacks by L. neoniger and Formica pallidifulva nitiventris Emery, but were invariably killed during encounters with Formica schaufussi Mayr and Formica subsericea Say, larger ants that are common in lawns and golf roughs. Predation on implanted Japanese beetle eggs also tended to be greater in roughs than in fairways, and fewer grubs were found in areas of golf roughs where ants were abundant than where ants had been controlled. This study suggests that predation by indigenous ants provides an important buffer against pest outbreaks on lawns and golf courses.

Contribution of ergot alkaloids to suppression of a grass‐feeding caterpillar assessed with gene knockout endophytes in perennial ryegrass

Neotyphodium and Epichloë species (Ascomycota: Clavicipitaceae) are fungal symbionts (endophytes) of grasses. Many of these endophytes produce alkaloids that enhance their hosts’ resistance to insects or are toxic to grazing mammals. The goals of eliminating from forage grasses factors such as ergot alkaloids that are responsible for livestock disorders, while retaining pasture sustainability, and of developing resistant turf grasses, require better understanding of how particular alkaloids affect insect herbivores. We used perennial ryegrass Lolium perenne L. (Poaceae) symbiotic with Neotyphodium lolii × Epichloë typhina isolate Lp1 (a natural interspecific hybrid), as well as with genetically modified strains of Lp1 with altered ergot alkaloid profiles, to test effects of ergot alkaloids on feeding, growth, and survival of the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), a generalist grass‐feeding caterpillar. Neonates or late instars were provided clippings from glasshouse‐grown plants in choice and rearing trials. Wild‐type endophytic grass showed strong antixenosis and antibiosis, especially to neonates. Plant‐endophyte symbiota from which complex ergot alkaloids (ergovaline and lysergic acid amides such as ergine) or all ergot alkaloids were eliminated by endophyte gene knockout retained significant resistance against neonates. However, this activity was reduced compared to that of wild‐type Lp1, providing the first direct genetic evidence that ergot alkaloids contribute to insect resistance of endophytic grasses. Similarity of larval response to the two mutants suggested that ergovaline and/or ergine account for the somewhat greater potency of wild‐type Lp1 compared to the knockouts, whereas simpler ergot alkaloids contribute little to that added resistance. All of the endophyte strains also produced peramine, which was probably their primary resistance component. This study suggests that ergot alkaloids can be eliminated from an endophyte of perennial ryegrass while retaining significant insect resistance.