Loke T. Kok

Lethal and Sublethal Effects of Imidacloprid on Hemlock Woolly Adelgid (Hemiptera: Adelgidae) and Two Introduced Predator Species

ABSTRACT Eastern hemlock, Tsuga canadensis (L.) Carrière, branchlets were systemically treated with imidacloprid and bioassayed with hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae), and predators. After 10 d, two hemlock woolly adelgid predators, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae Sasaji & McClure (Coleoptera: Coc-cinellidae), were allowed to feed on remaining hemlock woolly adelgid for 20 d on branches systemically treated with 1, 10. or 100 ppm imidacloprid. Every 5 d, mortality, mobility (measured as flip time), number of hemlock woolly adelgid consumed, and degree of intoxication of each individual beetle were recorded. Liquid chromatography-mass spectrometry was used to quantify imidacloprid and some of its major metabolites in hemlock wood tissues and in the predator beetles postmortem. Probit analysis of hemlock woolly adelgid mortality and imidacloprid concentrations recovered from branch wood tissues determined the 30 d LC50 to be 242 ppb. A topical application of imidacloprid to the ventral abdomen of individual beetles resulted in a 6 d LD50 value of 1.8 and 0.71 ng imidacloprid per beetle for L. nigrinus and S. tsugae, respectively. In no-choice tests, L. nigrinus mortality was significantly higher on hemlock branchlets treated with 100 ppm imidacloprid than on controls, but S. tsugae mortality was not. S. tsugae consumed the same number of adelgids on treated branchlets as on controls, but L. nigrinus consumed fewer adelgids from the 100 ppm branchlets than on controls. In choice tests, beetle mortality and flip times were generally not significantly different from controls. At times, both beetle species displayed intoxication symptoms after feeding on adelgids from treated branchlets and imidacloprid was recovered from both beetle species postmortem. These results suggest that systemic imidacloprid displayed both lethal and sublethal effects on these two nontarget predators of the hemlock woolly adelgid.

Road Survey of the Invasive Tree-of-Heaven (Ailanthus altissima) in Virginia

Abstract Tree-of-heaven is an invasive, nonnative species that invades newly disturbed areas and forms large monospecific stands. It was surveyed from a vehicle along 5,175 km of roads in Virginia in 2004, 2005, 2010, and 2011. Fifty-eight percent of every 1.6-km road segment had at least one tree-of-heaven. Mean density of tree-of-heaven throughout the roads surveyed in Virginia was 39 km−1. The interaction between road classification (interstate, primary, and secondary) and physiographic region (mountain, piedmont, and tidewater) was significant; consequently, the density of tree-of-heaven along the different road classifications depended on the effect of the physiographic region and vice versa. Tree-of-heaven was fairly evenly distributed throughout Virginia ranging from 39 to 78% of 1.6-km road segments infested, but had a greater variation in density. Current areas with low densities could increase in density in the future. The highest density of tree-of-heaven was along interstate highways in the mountains (85 km−1), followed by the tidewater (63 km−1), and piedmont (46 km−1) regions. Primary roads had a moderate density of tree-of-heaven with a range of 24 to 36 km−1. Secondary roads had lower densities with 12 km−1 and 41 km−1 in the tidewater and mountain regions, respectively. Tree-of-heaven spreads primarily by wind-dispersed seeds from female trees, and populations bordering roadsides could serve as seed sources for further local and landscape spread. Nomenclature: Tree-of-heaven, Ailanthus altissima (P. Mill.) Swingle Management Implications: The invasive nonnative tree-of-heaven invades newly disturbed areas and forms large monospecific stands. The mean density of tree-of-heaven throughout the 5,175 km of roads surveyed in Virginia was 39 km−1 with mean infestation of 58% of 1.6-km road segments. Interstate highways had the highest tree-of-heaven densities and high infestation frequencies. Populations bordering the roads serve as seed sources for further dispersal along roads and into open and forested areas. Efforts to minimize the impact and spread of tree-of-heaven should be concentrated along the leading edge of infestations. Chemical applications and felling of mature female trees would reduce seed dispersal along roads and into adjacent forests. Reducing the amount of disturbed soil and quickly reseeding with native seeds would help in reducing new invasions of tree-of-heaven.

Contamination Delays the Release of Laricobius osakensis for Biological Control of Hemlock Woolly Adelgid: Cryptic Diversity in Japanese Laricobius spp. and Colony-Purification Techniques

Abstract Laricobius osakensis (Coleoptera: Derodontidae) was imported from Japan to the United States in 2006 for study in quarantine facilities as a potential biological control of Hemlock Woolly Adelgid. Laricobius osakensis was released from quarantine in 2010, but it was soon discovered that the colony also contained a cryptic species, Laricobius naganoensis. This led to the placement of L. osakensis back into quarantine and development of a method to purify the colony. To distinguish the two species, we designed a restriction fragment length polymorphism (RFLP) assay using mitochondrial DNA sequences and developed a non-lethal testing method. Twenty-one diagnostic nucleotide sites separated the two species, and they both exhibited extraordinary intra-specific haplotype diversity. Sequencing the ITS2 nuclear region did not produce evidence of hybridization between the species in the field or in the lab colony. Splitting the colony into small groups and testing their species composition was successful in isolating L. osakensis. Efforts should be made to maintain high genetic diversity in L. osakensis colonies. Continued genotyping of new colony stock will be necessary to fully characterize the diversity within both species.

Host plants and associated trophobionts of the weaver ants Oecophylla spp. (Hymenoptera: Formicidae)

Weaver ants (Oecophylla spp.) are often found on plants with insect symbionts (trophobionts), but the extent of such associations is not known. Examination of literature records of weaver ant host plants from 1900 to 2006 revealed that Oecophylla smaragdina, native to Asia, was recorded on 175 plant species in 46 families, with 28 associated trophobiont species in 7 families. Oecophylla longinoda, native to Africa, was recorded on 66 plant species in 34 families with 17 associated trophobiont species in 6 families. Both Oecophylla spp. shared host records on 17 economically important plant species. Such host plants could be used to augment establishment of weaver ants, facilitating their role as deterrents of phytophagous insect pests of economically important plants. O. smaragdina-tended trophobionts were recorded associating with the ants on several crops but rarely considered to be pests. Thus, the risk of trophobionts associated with Oecophylla ants being pests is considered minimal.