In-gallery social behaviors of the ambrosia beetle, Xylosandrus germanus (Coleoptera: Curculionidae)

The east Asian ambrosia beetle Xylosandrus germanus (Blanford) was first detected in the United States in 1932. It now occurs across much of eastern North America and parts of the Pacific Northwest. It attacks a broad range of stressed, woody hosts including ornamental and orchard species. The foundress tunnels into the sapwood of hosts where it cultures a symbiotic fungus as food for its offspring. A few other ambrosia beetles have been shown to possess a facultatively eusocial structure among gallery members, but this has not been described for Xylosandrus spp. Using a novel artificial diet arena, we quantified the behaviors of X. germanus larvae and adults (foundress and mature offspring) over 10 wk inside their galleries. Foundresses were responsible for constructing the gallery. They also initially tended the fungal garden and brood but eventually spent most of their time blocking the gallery entrance. Larvae were mainly observed to feed, crawl, or be inactive within the gallery, regardless of the absence or presence of adult siblings. Adult female offspring were primarily inactive, likely due to dormancy. Adult male offspring actively crawled and attempted to mate with their sisters before eventually dispersing out of the gallery. Cooperative hygienic behaviors (removal of frass, cannibalism of dead nest mates, grooming siblings) were observed but a division of labor among offspring was not clear. Rather, foundress behaviors were mostly distinct from offspring behaviors, particularly as the gallery aged. Because no overlap in generations occurred, X. germanus displays a quasisocial structure.

Closely related invasive species may be controlled by the same demographic life stages

Invasive species that are closely related to each other may have similar population dynamics and, therefore, be controlled by targeting similar life stages. We studied two invasive knapweed species, spotted knapweed (Centaurea stoebe subsp. micranthos) and the hybrid meadow knapweed complex (Centaurea × moncktonii) in New York, USA, to determine their individual population growth rates (λ) across several sites over three years. Both knapweed species had growth rates that were greater than 1 (spotted knapweed λ ranged from 1.005–1.440; meadow knapweed λ ranged from 1.541–2.408), but there was high variability between years and sites. One study population of meadow knapweed was composed primarily of individuals of black knapweed ancestry (C. nigra), a species that, while introduced, is not invasive. For this population, the projected dynamics were stable (λ approximately 1). Elasticity analysis showed that the flowering-to-flowering stage contributed the most to population growth rate for six of seven sites and three additional transitions were also influential for four of seven sites of spotted and meadow knapweed: the seedling-to-vegetative stage, vegetative-to-flowering stage and flowering-to-seedling stage. We simulated how increasing vital rates would affect population growth and found that both spotted and meadow knapweed followed the same pattern. The vital rate of established seedlings maturing to flowering plants had the greatest effect on population growth, followed by the survival of new and established seedlings. In all cases, the responses were non-linear, with small initial changes having a large effect. Increases in the vital rates of later stages also tended to have a positive effect on growth rate, but the effects were more modest. Although the sensitivity analysis indicated that early vital rates had the largest effect on population growth, targeting these stages is not practical for management. Rather, reducing older life stage survival or delaying maturation of vegetative individuals would be more effective. The similarity between the population dynamics and how each life stage contributes to population growth provides support that protocols developed for one species should be effective for the other species with the caveat that any biological control agent should be directly tested on the target species before being utilised.

Invasive swallow-worts: an allelopathic role for -(-) antofine remains unclear

Pale swallow-wort (Vincetoxicum rossicum) and black swallow-wort (V. nigrum) are two invasive plant species in the northeastern United States and eastern Canada that have undergone rapidly expanding ranges over the past 30 years. Both species possess a highly bioactive phytotoxin -(-) antofine in root tissues that causes pronounced inhibition in laboratory bioassays of native plant species co-located in habitats where swallow-wort is found. To further evaluate the allelopathic potential of -(-) antofine, we: determined its concentration in young plant tissues; used in situ approaches to assess antofine stability, potential activity of degradation products, activity in sterile and nonsterile soil; and determined accumulation and concentration in hydroponic cultivation and field collected soil samples. Extracts of seeds and young seedlings were found to have approximately 2-3 times the level of -(-) antofine in comparison to root extracts of adult plants. Breakdown products of antofine accumulated rapidly with exposure to light, but more slowly in the dark, at ambient temperatures, and these products did not retain biological activity. Extraction efficiencies of control soil spiked with -(-) antofine were low but easily detectable by HPLC. Soil samples collected over two growing seasons at four different sites where either pale swallow-wort or black swallow-wort populations are present were negative for the presence of -(-) antofine. Dose response curves using sterile and nonsterile soil spiked with -(-) antofine demonstrated a requirement for at least 20-55 × greater -(-) antofine concentrations in soil to produce similar phytotoxic effects to those previously seen in agar bioassays with lettuce seedlings. Sterile soil had a calculated EC50 of 686 μM (250 μg/g) as compared to nonsterile soil treatments with a calculated EC50 of 1.88 mM (640 μg/g). When pale swallow-wort and black swallow-wort adult plants were grown in hydroponic cultivation, -(-) antofine was found in root exudates and in the growing medium in the nM range. The concentrations in exudate were much lower than that needed for biological activity (μM) although they might be an underestimate of what may accumulate over time in an undisturbed rhizosphere. Based on these various results, it remains uncertain as to whether -(-) antofine could play a significant allelopathic role for invasive swallow-worts.

Development and reproduction of the foxglove aphid (Hemiptera: Aphididae) on invasive swallow-worts (Vincetoxicum spp.)

The foxglove aphid, Aulacorthum solani (Kaltenbach), recently was documented using the invasive species pale and black swallow-wort (Vincetoxicum rossicum (Kleopow) Barbar. and V. nigrum (L.) Moench, respectively) as host plants. Because these are new host plant records for this polyphagous species, we investigated foxglove aphid development and reproduction on pale and black swallow-wort relative to a known crop host, potato (Solanum tuberosum L.), at a 25:20°C thermophase and a photoperiod of 16:8 (L:D) h. Almost no such data have been previously reported for a noneconomic host plant. Larval development and survival, as well as adult reproductive development and fecundity, were similar between the two swallow-wort species and potato. Adult aphids lived significantly longer on pale swallow-wort than the other two host plants, but this extended longevity encompassed the postreproductive stage. Foxglove aphid population parameters were therefore similar among the three plant species as well as most previous reports on crop plants. Pale and black swallow-wort appear to be suitable secondary hosts for foxglove aphid; other factors possibly limit aphid abundance on these two plant species in the field.

First Report of Blight Caused by Sclerotium rolfsii on the Invasive Exotic Weed, Vincetoxicum rossicum (Pale Swallow-Wort), in Western New York

Pale (Vincetoxicum rossicum) and black swallow-wort (V. nigrum) are perennial, twining vines that are increasingly invasive in natural and managed ecosystems in the northeastern United States and southeastern Canada. Both species, introduced from Europe in the 1800s, are listed as noxious weeds or banned invasive species by the USDA-Natural Resource Conservation Service. Observations by C. Southby, a local naturalist, over several years at a meadow populated by pale swallow-wort in Powder Mill Park, Monroe County, NY, revealed a gradual disappearance of pale swallow-wort with restoration of native grasses and some dicotyledonous plant species, in a 6.7-m-diameter area. Diseased swallow-wort plants had extensive yellowing and wilting of foliage, likely due to splitting of the basal stem, with white mycelium throughout the stem and crown; small, reddish brown sclerotia were evident, but roots were not affected. Stem tissue sections from 20 symptomatic plants were vacuum infiltrated with 2% NaOCl for 20 min, then plated onto malt yeast agar and potato dextrose agar amended with 60 mg/liter of penicillin and 80 mg/liter of streptomycin, resulting in development of fast-growing, white mycelium which then formed numerous, irregularly shaped (2 to 4 mm diameter), reddish brown sclerotia at the plate edges. Two individual cultures were identified as S. rolfsii (1) based on size, shape, and color of the sclerotia and presence of characteristic clamp connections in the mycelium. The isolate was suspected to be S. rolfsii var. delphinii due to the reported inability of S. rolfsii to persist in regions with extremely low winter temperatures (4), but molecular data showed otherwise. Sequences of the 18S gene (GenBank JN543690), internal transcribed spacer region (JN543691), and 28S gene (JN543692) of the ribosomal DNA identified the isolate, VrNY, as S. rolfsii (2,3). Pathogenicity tests were conducted with individual 2-month-old seedlings of V. rossicum and V. nigrum grown in steam-sterilized Metromix 360 in SC10 polypropylene conetainers in a growth chamber with a diurnal cycle of 25/20°C, a photoperiod of 14-h light/10-h dark, and fertilized at 3 week intervals. Two independent replications of 12 plants of each species were each inoculated at the stem base with a 4-mm-diameter mycelial agar plug from the growing edge of a colonized plate. The agar plug was held in place with 5 g of sterile sand. Control plants (12 of each species per replication) were treated with sterile agar plugs. Plants for each treatment were placed within a clear plastic bag to maintain 90% relative humidity for 72 h, and then removed from the bags. Disease symptoms developed over 21 days, with >90% of inoculated plants showing symptoms within 2 weeks. Control plants were symptomless. Incidence of mortality was 66 and 60% for V. rossicum and V. nigrum, respectively, by 3 weeks. The fungus reisolated from diseased stem and crown tissue produced characteristic mycelium with irregular sclerotia, consistent with those of S. rolfsii. Since spread of this fungus is based on movement of soilborne sclerotia, this isolate may offer potential as a bio-herbicide for control of swallow-wort in natural ecosystems if the isolate can be demonstrated to have a host range restricted to this invasive weed. References: (1) B. A. Edmunds and M. L. Gleason. Plant Dis. 87:313, 2003. (2) C. E. Harlton et al. Phytopathology 85:1269, 1995. (3) I. Okabe and N. Matsumoto. Mycol. Res. 107:164, 2003. (4) Z. Xu et al. Plant Dis. 92:719, 2008.

Phytophagous arthropods of invasive swallow-wort vines (Vincetoxicum spp.) in New York

Pale swallow-wort (Vincetoxicum rossicum [Kleopow] Barbar.) and black swallow-wort (V. nigrum [L.] Moench), European species of herbaceous, perennial viny milkweeds, have become increasingly invasive in various natural and managed habitats in the northeastern United States and southeastern Canada, including low- and high-light habitats. A classical biological control program is being developed, but almost no information was available on the current arthropod fauna for either species in the invaded range. I conducted quantitative surveys on pale and black swallow-wort at several locations in New York State over 3 yr to identify and compare the seasonal assemblage of phytophagous arthropods that are feeding and developing on the plants in sunny and shaded habitats. Of the approximately 84 nonpredatory species collected, 10 polyphagous, ectophagous species of native and exotic arthropods were identified, exclusively from the leaves or stems, which could develop to the adult stage and in most cases complete at least one generation on one or both species of swallow-wort. However, their densities were low throughout the season and generally did not differ between the sunny and shaded habitats. Very little to no damage was observed on the plants. Exotic swallow-worts seem to have been released from specialized natural enemies and have not accrued a damaging suite of generalist herbivores. This may be a contributing factor in the increasing invasiveness of these weeds, and biological control appears promising for these plants.

Overwintering survival, phenology, voltinism, and reproduction among different populations of the leaf beetle Diorhabda elongata (Coleoptera: Chrysomelidae)

The classical biological control program for exotic saltcedars (various Tamarix species and hybrids) has involved the assessment of different populations of the leaf beetle Diorhabda elongata (Brullé) s.l. that are promising for release in areas of North America that are located south of 37 degrees N latitude. We report here the overwintering survival, phenology, and voltinism of four D. elongata populations (Tunisia, Crete, Uzbekistan, and Turpan) in eastcentral Texas. In addition, we studied their developmental and reproductive biology, which also included the previously released population from Fukang, China. Overwintering survival of the adult beetles of the Crete and Tunisia populations was 90-99 and 75%, respectively. The Uzbekistan and Turpan beetles had <31% overwintering survival. All D. elongata populations began ovipositing in late March. The Turpan beetle may produce three summer generations and ceased oviposition by September. The Crete beetle produced four summer generations plus a partial fifth generation and ceased ovipositing by mid-October. Both the Tunisia and Uzbekistan beetles produced five summer generations plus an unsuccessful partial sixth generation; oviposition extended into late November. Larval development and survival were generally similar among D. elongata populations. The Turpan and Fukang beetles had a shorter preoviposition period and produced more but smaller egg masses than the other beetle populations. However, this did not alter a female's lifetime fecundity and generally did not affect the innate capacity for increase compared with other populations. The Crete beetle seems to be the most promising for release in central Texas and points further south.