L. T. Kok

Evaluation of trap crops to manage harlequin bugs, Murgantia histrionica (Hahn) (Hemiptera: Pentatomidae) on broccoli

Abstract Broccoli (Brassica oleracea ‘Packman Hybrid’), mustard (B. kabar ‘Southern Giant Curled’), and rape (B. napus ‘Dwarf Essex’) were evaluated as trap crops to manage harlequin bugs,Murgantia histrionica (Hahn), in broccoli field plots during 1994 and 1995 in Montgomery County, Virginia. Mustard and rape prevented low densities of harlequin bugs from reaching the main broccoli crop, but at high densities harlequin bugs moved from the trap plants into the primary crop. This indicates that harlequin bugs attracted to trap plants may damage the main crop if their numbers reach relatively high levels.

Host-range testing of Eucryptorrhynchus brandti (Coleoptera: Curculionidae), a candidate for biological control of tree-of-heaven, Ailanthus altissima.

ABSTRACT Ailanthus altissima (Mill.) Swingle, tree-of-heaven, is an invasive species native to Asia. It first was introduced into the United States in the 1700s and now is distributed throughout much of North America. Mechanical and chemical controls are current suppression tactics, however, implementation is costly. A weevil, Eucryptorrhynchus brandti (Harold), was identified in China and imported for quarantine testing in 2004 as a potential biological control agent. Host specificity tests on adult feeding, larval development, and oviposition of this weevil were conducted from 2007 to 2011 on A. altissima and 29 nontarget species. Eucryptorrhynchus brandti adults fed significantly more on A. altissima foliage when compared with all test species. Range of means for feeding on A. altissima was 32.5–106.5 mm2/adult/d. In no-choice tests, Simarouba glauca DC, Leitneria floridana Chapm., and Citrus limon (L.) Burm. F., had feeding rates of only 10, 49, and 10%, respectively, compared with the level of feeding on A. altissima. The mean range of adult feeding by E. brandti on all other test species was <7% of feeding on A. altissima (0.0–3.3 ± 5.0 mm2/adult/d). In the no-choice larval inoculation tests, larval development only occurred in two of 10 L. floridana seedlings compared with seven of 10 A. altissima seedlings. In the no-choice oviposition tests, oviposition and subsequent larval development did not occur in L. floridiana, whereas all seven A. altissima seedlings supported oviposition and subsequent larval development. The weevil did not appear to be a threat to L. floridana or any other nontarget species tested. Therefore, we conclude that Eucryptorrhynchus brandti is highly host specific to A. altissima.

Spatiotemporal distribution of the hemlock woolly adelgid predator Laricobius nigrinus after release in eastern hemlock forests

1 Post‐release distributions of Laricobius nigrinus, a biological control predator of hemlock woolly adelgid Adelges tsugae Annand, were evaluated at eight hemlock forests in the eastern U.S.A. 2 Vertical dispersal of F1 and F2L. nigrinus were assessed from within three crown strata (<7, 7–15 and >15 m) at four release sites. 3 Horizontal distributions of L. nigrinus within the forest surrounding central release areas were observed in two separate studies, which included (i) release and monitor to capture parent and F1 movement by sampling the immature life stages of the offspring, and (ii) assessment of F3 to F6 generations where beetles were previously determined to be established. 4 Laricobius nigrinus, released on lower crown branches, oviposited within the upper crown stratum and were slow to disperse from release trees. Monitoring L. nigrinus only from the lower crown would likely underestimate its presence because 86% of the F2 generation were detected above 15 m. 5 By the fifth generation, the frequency distributions of larvae increased at increasing distance from release areas; larvae were recovered at a maximum distance of approximately 400 m and the spread rate was approximately 39 m/year. 6 Slow dispersal of L. nigrinus and uninterrupted recovery of six generations in the presence of fluctuating prey density support its continued release as part of the A. tsugae biological control programme. These data contribute toward improved release strategies and monitoring for this biological control agent.

Impacts of Trunk and Soil Injections of Low Rates of Imidacloprid on Hemlock Woolly Adelgid (Hemiptera: Adelgidae) and Eastern Hemlock (Pinales: Pinaceae) Health

ABSTRACT Eastern hemlocks (Tsuga canadensis Carrière) at two sites in southwestern Virginia were treated by trunk and soil injections of imidacloprid to determine the insecticides impact on hemlock woolly adelgid, Adelges tsugae Annand. Treatments were 25, 50, and 100% of the highest labeled dosage rates for both stem and soil injection. Three and 4 yr after treatment, the half and full rates had significantly reduced A. tsugae populations, which were accompanied by increased new hemlock shoot growth and higher hemlock health scores on a visual rating of tree appearance. Imidacloprid and metabolite concentrations in tissue of treated trees were determined by liquid chromatography—tandem mass spectrometry, and A. tsugae density decreased as imidacloprid concentrations increased in wood tissue. There were no observed A. tsugae populations in all trees with imidacloprid tissue concentrations >413 ppb. Olefin, di-hydroxy, and 6-chloro-nicotinic-acid metabolites were the imidacloprid metabolites recovered in the highest concentrations. This suggests that hemlock metabolism of imidacloprid may increase efficacy of the parent compound. Stem and soil treatments of low rates of systemic imidacloprid reduce adelgid populations and promote hemlock health, but still may provide a remnant food source for beneficial predators.

Successful biological control of plumeless thistle, Carduus acanthoides L. [Campanulatae: Asteraceae (= compositae)], by Trichosirocalus horridus (Panzer) (Coleoptera: Curculionidae) in Virginia

Abstract The plumeless thistle, Carduus acanthoides L., is a major weed of pastures, highway median strips, and road sides in much of western Virginia. It occupies a range similar to that of musk thistle, Carduus thoermeri Weinmann, and is often found together with musk thistle. A 15-year study at five sites with releases of Trichosirocalus horridus (Panzer), a ceutorhynchine weevil introduced into North America for the biological control of both musk and plumeless thistles, showed excellent control of plumeless thistle with mean ± SD reductions of 95 ± 4.9%, range 87–100%. Average initial thistle densities during weevil releases in 1975–1977 compared with those in 1990 were 8.7 and 0.3/m2, respectively. Mean time for the plumeless thistle population to collapse was 10.8 ± 2.3 (range 7–13) years compared with about half that for musk thistle.

Assessing Eucryptorrhynchus brandti (Coleoptera: Curculionidae) as a potential carrier for Verticillium nonalfalfae (Phyllachorales) from infected Ailanthus altissima

Abstract Two potential biological control agents for the invasive tree-of-heaven, Ailanthus altissima (Mill.) Swingle, have been extensively studied: a vascular wilt fungus, Verticillium nonalfalfae Inderb. (formerly Verticillium albo-atrum Reinke and Berthold), and a host-specific weevil from China, Eucryptorrhynchus brandti Harold, which is currently pending quarantine release. In 2002, V. nonalfalfae was observed in Pennsylvania causing significant mortality to A. altissima. Quarantine experiments were conducted to test different forms of transmission of the fungus by E. brandti to A. altissima. In one experiment, 75% of adult E. brandti transmitted V. nonalfalfae to A. altissima seedlings after contact with a culture and feeding on infected plant material. In another study, 14.7±1.3% of adult E. brandti ingested and passed viable V. nonalfalfae propagules into faeces after feeding on infected A. altissima stems for 24, 48 and 72 h, respectively, and the number of propagules increased at 72 h. Eighty-three per cent of surviving weevils overwintering in naturally infested potting mix carried viable V. nonalfalfae propagules externally. All weevil progeny that emerged from infected A. altissima billets appeared to be as healthy as weevils reared from non-infected billets. Our studies have shown that ingestion of V. nonalfalfae after feeding on infected plant material plays an important role in assessing E. brandti as a potential carrier. Results from these laboratory studies indicate E. brandti has the ability to transfer V. nonalfalfae to A. altissima seedlings in a laboratory setting.

Laboratory Rearing of Laricobius nigrinus (Coleoptera: Derodontidae): A Predator of the Hemlock Woolly Adelgid (Hemiptera: Adelgidae)

Coleopteran species are biological control agents of numerous invasive pests. Laricobius nigrinus (Coleoptera: Derodontidae), a predaceous, univoltine species, spends the summer aestivating but is active for the rest of the year. Laricobius nigrinus possesses many essential attributes for effective biological control of the hemlock woolly adelgid (Hemiptera: Adelgidae). The predator must be reared in large numbers for field releases. We describe some of the studies that led to the successful procedures currently used for mass rearing L. nigrinus.

Cultivar preferences of lepidopterous pests of broccoli

Selected cultivars of broccoli grown in Halifax County (south-central Virginia) and Montgomery County (southwestern Virginia) from 1986 to 1988 were sampled regularly for insects to compare cultivar (cv.) preference of the lepidopterous pests. The imported cabbageworm, Pieris rapae (L.), was the most abundant pest of broccoli in Montgomery Co. during five consecutive spring and autumn plantings. In the autumn plantings in Halifax Co. the cabbage looper, Trichoplusia ni (Hubner), and the cabbage webworm, Hellula rogatalis (Hulst), were most abundant in 1987, and the cabbage looper and the imported cabbageworm were most abundant in 1988. Other Lepidoptera encountered in low numbers were the diamondback moth, Plutella xylostella (L.); the cross-striped cabbageworm, Evergestis rimosalis (Guenee); and the corn earworm, Heliothis zea (Boddie). Counts of imported cabbageworm eggs showed some differences between cvs in Montgomery Co., but not in Halifax Co., nor was there any difference for cabbage looper eggs. Mean larval counts (sum of small and large larvae of Lepidoptera per plant per sample date) for each season showed significant differences between the 13 cvs tested. The level of insects infesting the plants corresponded to the maturity dates of the cvs: more larvae per sample date were found on the late-maturing cvs than the early-maturing cvs. Symphony, an early-maturing cv., had the least number of larvae whereas Green Defender, a late-maturing cv., had the most. The mid-maturing cvs had intermediate levels of insects. No significant differences in leaf defoliation, yield, or percentage marketable heads were found between cvs.

Assessing Performance and Competition Among Three Laricobius (Coleoptera: Derodontidae) Species, Predators of Hemlock Woolly Adelgid, Adelges tsugae (Hemiptera: Adelgidae)

ABSTRACT Predation, egg production, and survivorship of Laricobius nigrinus Fender, L. rubidus LeConte, and L. osakensis Montgomery and Shiyaki, predators of hemlock woolly adelgid, Adelges tsugae Annand, were investigated in the laboratory and in the field. In individual assays in the laboratory, L. rubidus oviposited fewer eggs than either L. nigrinus or L. osakensis. In assays containing congeneric or conspecific groups of adult Laricobius, L. osakensis preyed upon the greatest number of ovisacs. The number of ovisacs preyed upon was not different between treatments with all three species and those with only L. osakensis or L. nigrinus. Adult predators fed on few predator eggs and when they did no species preference was observed. The numbers of A. tsugae ovisacs fed upon did not differ significantly by groups of congeneric or conspecific Laricobius larvae. Laricobius adults and larvae had high survival rates throughout all experiments. In the field, L. nigrinus and L. rubidus were enclosed in sleeve cages with both high (>120 ovisacs) and low (<90 ovisacs) A. tsugae densities for 1 wk. All branches with caged beetles had significantly greater numbers of ovisacs preyed upon than branches caged without beetles. No differences in predation or egg production were found among the conspecific and congeneric groupings. Predation was uniformly greater on high prey-density branches than on low prey-density branches. Survivorship among predators did not differ significantly at either prey density. Results from both laboratory and field experiments suggest that these species are able to coexist and can be released in the same location for biological control of A. tsugae.

Evaluation of ELISA for imidacloprid detection in eastern hemlock (Tsuga canadensis) wood and needle tissues

BACKGROUND Imidacloprid is the primary insecticide used against the exotic invasive insect hemlock woolly adelgid, Adelges tsugae Annand, a pest of eastern hemlock [Tsuga canadensis (L.) Carrière] trees in the eastern United States. A competitive enzyme-linked immunosorbent assay (ELISA) was evaluated for quantification of imidacloprid in eastern hemlock wood and needle tissues. RESULTS Matrix effects in the form of false positives and overestimated imidacloprid concentrations were observed in both wood and needle extracts. Tissues required a 100-1000-fold dilution with water in order to reduce matrix effects. Standard curves in 1% wood or needle extract were not significantly different from standard curves prepared in water. Matrix effects were more pronounced at concentrations in the lower working range of the kit, with recovery of 5 microg L(-1) imidacloprid more accurate than recovery of 0.2 microg L(-1). CONCLUSION ELISA remains a valuable tool for semi-quantitative imidacloprid detection within the hemlock system because of its sensitivity, cost and ease of use. However, a 1000-fold dilution of hemlock tissue extract is recommended to ensure accurate imidacloprid determinations.