Sandy M. Smith

A heterozygous moth genome provides insights into herbivory and detoxification

How an insect evolves to become a successful herbivore is of profound biological and practical importance. Herbivores are often adapted to feed on a specific group of evolutionarily and biochemically related host plants, but the genetic and molecular bases for adaptation to plant defense compounds remain poorly understood. We report the first whole-genome sequence of a basal lepidopteran species, Plutella xylostella, which contains 18,071 protein-coding and 1,412 unique genes with an expansion of gene families associated with perception and the detoxification of plant defense compounds. A recent expansion of retrotransposons near detoxification-related genes and a wider system used in the metabolism of plant defense compounds are shown to also be involved in the development of insecticide resistance. This work shows the genetic and molecular bases for the evolutionary success of this worldwide herbivore and offers wider insights into insect adaptation to plant feeding, as well as opening avenues for more sustainable pest management.

Host Volatile Attractants and Traps for Detection of Tetropium fuscum (F.), Tetropium castaneum L., and Other Longhorned Beetles (Coleoptera: Cerambycidae)

Abstract Cortical and sapwood volatiles were collected in situ from red spruce, Picea rubens (Sarg.), trees infested with Tetropium fuscum (F.), to determine the relative concentrations and enantiomer ratios of monoterpenes emitted. This information was used to create a synthetic “spruce blend” lure that was tested in various trap designs for efficacy in capturing T. fuscum, and Tetropium castaneum L. in field bioassays conducted on McNabs Island, Nova Scotia, in 2001 and 2002 and in Poland and Switzerland in 2002. Response of other cerambycid species was measured opportunistically. Cross-vane pan traps baited with spruce blend caught significantly more T. fuscum than unbaited traps or traps baited with racemic α-pinene, ethanol, or both. The addition of an ethanol lure to spruce blend–baited traps significantly increased capture of T. fuscum and T. castaneum. There were no significant differences among trap designs in mean catch of either Tetropium species. Spruce blend was also significantly attractive to Monochamus urussovii (Fischer) and, when paired with an ethanol lure, was significantly attractive to Spondylis buprestoides L. Asemum striatum L. was significantly attracted to racemic α-pinene but was not attracted to spruce blend or spruce blend plus ethanol. None of the lures tested were significantly attractive to Stictoleptura rubra L. or Alosterna tabacicolor (DeGeer).

Effect of host availability on reproduction and survival of the parasitoid wasp Trichogramma minutum

Abstract. 1 We tested the hypothesis that females of the egg parasitoid, Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae), could adjust their fecundity schedule according to host availability and that there was a negative correlation between reproduction and survival in these wasps. 2 Newly‐emerged females were provided with an unlimited or limited number of hosts in the first trial and with either unlimited, limited or zero hosts in the second trial. 3 When hosts were unlimited, wasps had the highest rate of reproduction in the first day, which decreased dramatically thereafter. When hosts were limited, wasps from the two trials differed in their response. In Trial I, females with limited hosts had lower first‐day fecundity than, and the same subsequent‐day fecundity as, those with unlimited hosts. However, in Trial II, females with limited host had a lower first‐day but a higher subsequent‐day fecundity than those with unlimited hosts. This indicates variation in Trichogrammas ability to shift its fecundity schedule in response to host availability. 4 There was a positive (rather than a negative) correlation between reproduction and survival. Wasps that oviposited (in host‐unlimited treatment) had greater longevity than those that could not (in host‐unavailable treatment). 5 The sex ratio of the progeny produced by wasps in both host‐unlimited and limited treatments shifted gradually from a female to a male bias as the wasps aged. 6 We consider the ability of parasitoids to adjust their fecundity schedule as an adaptation to changing host resources and discuss our findings with regard to theories of life history evolution.

Community Composition of Longhorned Beetles (Coleoptera: Cerambycidae) in the Canopy and Understorey of Sugar Maple and White Pine Stands in South-Central Ontario

Abstract Insects of forest canopies are poorly known, especially in temperate forests of eastern North America. From June to August 2001, we sampled Cerambycidae using paired canopy and understorey flight-interception traps in nine pine and nine maple sites in south-central Ontario. Canopy traps were set using a simple ground-based bow-and-arrow method, and averaged 24.5 m in height at pine sites and 20.5 m at maple sites. In total, 297 individuals from 28 species were collected during 6 wk of sampling. Clytus ruricola (Olivier) accounted for 37% of all individuals. Pine sites had more species and higher expected richness than maple sites but significantly fewer individuals. Ten species were unique to pine, six to maple, and 12 occurred in both forest types. The two trap heights had similar observed richness, but expected richness was higher for canopy than understorey traps. Understorey traps accumulated significantly higher abundances than canopy traps. Eleven species were unique to canopy traps, 11 to understorey traps, and six occurred at both heights. Species accumulation was much faster when both heights were sampled compared with either alone. Anthophylax attenuatus (Newman), which has been rarely caught in other studies, was collected only in the canopy and was relatively abundant. Top collecting bottles on traps yielded similar observed richness as bottom bottles but had higher expected richness. Several species showed strong associations with either top or bottom collecting bottles. Species accumulation rates appeared to be higher than in other studies. Our results emphasize the necessity of including the canopy fauna in diversity studies.

Differences Between Forest Type and Vertical Strata in the Diversity and Composition of Hymenpteran Families and Mymarid Genera in Northeastern Temperate Forests

Abstract Most insects’ assemblages differ with forest type and show vertical stratification. We tested for differences in richness, abundance and composition of hymenopteran families and mymarid genera between sugar maple (Acer saccharum) and white pine (Pinus strobus) stands and between canopy and understory in northeastern temperate forests in Canada. We used flight interception traps (modified malaise traps) suspended in the canopy and the understory in a split-split block design, with forest type as the main factor, forest stratum as the first split factor, and collection bottle location as the second split factor. Hymenopteran families and mymarid genera differed in their diversity depending on forest type and stratum. Both family and genera richness were higher in maple than in pine forests, whereas family richness was higher in the canopy and top bottles and generic richness was higher in the understory and bottom bottles. Multivariate analysis separated samples by forest type, vegetation stratum, and bottle location. Family composition showed 77% similarity between forest types and 73% between the canopy and understory. At the lower taxa level, mymarid genera showed only 47% similarity between forest types and 40% between forest strata, indicating vertical stratification and relatively high β-diversity. Our study suggests that hymenopteran diversity and composition is strongly dependent on forest type and structure, making flying members of this order particularly vulnerable to forest management practices. It also shows that insect assemblage composition (especially at low-taxon levels), rather than relative abundance and richness, is the community attribute most sensitive to forest type and vertical stratification.

Natural Enemies Associated with Sirex noctilio (Hymenoptera: Siricidae) and S. nigricornis in Ontario, Canada

ABSTRACT Sirex noctilio F. is an exotic woodwasp now found in eastern North America where it shares natural enemies with native woodwasps of Pinus spp. To study the extent to which native hymenopteran parasitoids and parasitic nematodes could affect woodwasp populations, 60 Pinus trees with symptoms of S. noctilio attack were felled in 2007 and 2008 in Ontario, Canada. Each tree bole was cut into 1-m sections that were placed in individual rearing tubes; emergence was monitored from May to November of the year of felling. Female S. noctilio were dissected to assess parasitism by the nematode Deladenus siricidicola Bedding. Two species of Siricidae emerged from these trees; S. noctilio, which accounted for most of the specimens collected, and S. nigricornis F. Of the three species of parasitoid that emerged, Ibalia leucospoides (Hochenwarth) was the most abundant, accounting for an overall hypothetical Siricidae parasitism rate of almost 20%. This parasitoid emerged over a similar time period as S. noctilio—between early July and early September. Except in trees >15 m in height, parasitism by I. leucospoides generally appeared uniform throughout the bole. Parasitism rates did not vary between the 2 yr, but did between sites in 1 yr. Parasitic nematodes were found in the haemocoel of about one third of S. noctilio females dissected but were never found sterilizing the eggs; none were found in S. noctilio emerging from P. resinosa. These findings suggest that I. leucospoides is currently the primary invertebrate natural enemy of S. noctilio in Ontario.

Evidence of interaction between Sirex noctilio and other species inhabiting the bole of Pinus

1 Sirex noctilio is a woodwasp native to Eurasia and Northern Africa and has recently been found infesting pines in eastern North America. Its pest status in this new range is not yet known, although it is an important pest in other areas where it has been introduced. Pinus spp. in North America are hosts to several native and alien species of subcortical insects. Interactions between the woodwasp and these species may influence its distribution or the characteristics of its life history, thus affecting its population dynamics over time. 2 Sixty S. noctilio‐infested Pinus spp. were felled in Ontario, Canada, and all phloem‐feeding and woodboring insects were collected and identified from each 1‐m section of the tree. 3 Sirex noctilio was in a tree alone 10% of the time but commonly shared the tree with subcortical beetles, such as Tomicus piniperda, Pissodes nemorensis, Ips grandicollis, Gnathotrichus materiarius and Monochamus carolinensis. The woodwasp was distributed throughout the tree stem and this distribution overlapped with that of the beetles. 4 Fewer but larger S. noctilio males emerged from trees with beetles compared with those without, although there was no statistical difference in females. 5 These findings suggest that co‐habiting beetles could negatively affect S. noctilio population dynamics over time. The potential mechanisms for this interaction are discussed.

The unseen invaders: introduced earthworms as drivers of change in plant communities in North American forests (a meta-analysis).

Abstract Globally, biological invasions can have strong impacts on biodiversity as well as ecosystem functioning. While less conspicuous than introduced aboveground organisms, introduced belowground organisms may have similarly strong effects. Here, we synthesize for the first time the impacts of introduced earthworms on plant diversity and community composition in North American forests. We conducted a meta‐analysis using a total of 645 observations to quantify mean effect sizes of associations between introduced earthworm communities and plant diversity, cover of plant functional groups, and cover of native and non‐native plants. We found that plant diversity significantly declined with increasing richness of introduced earthworm ecological groups. While plant species richness or evenness did not change with earthworm invasion, our results indicate clear changes in plant community composition: cover of graminoids and non‐native plant species significantly increased, and cover of native plant species (of all functional groups) tended to decrease, with increasing earthworm biomass. Overall, these findings support the hypothesis that introduced earthworms facilitate particular plant species adapted to the abiotic conditions of earthworm‐invaded forests. Further, our study provides evidence that introduced earthworms are associated with declines in plant diversity in North American forests. Changing plant functional composition in these forests may have long‐lasting effects on ecosystem functioning.

A gall-inducing arthropod drives declines in canopy tree photosynthesis

Mature forest canopies sustain an enormous diversity of herbivorous arthropods; however, with the exception of species that exhibit large-scale outbreaks, canopy arthropods are thought to have relatively little influence on overall forest productivity. Diminutive gall-inducing mites (Acari; Eriophyoidae) are ubiquitous in forest canopies and are almost always highly host specific, but despite their pervasive occurrence, the impacts of these obligate parasites on canopy physiology have not been examined. We have documented large declines in photosynthetic capacity (approx. 60%) and stomatal conductance (approx. 50%) in canopy leaves of mature sugar maple (Acer saccharum) trees frequently galled by the maple spindle gall mite Vasates aceriscrumena. Remarkably, such large impacts occurred at very low levels of galling, with the presence of only a few galls (occupying approx. 1% of leaf area) compromising gas-exchange across the entire leaf. In contrast to these extreme impacts on the leaves of adult trees, galls had no detectible effect on the gas-exchange of maple saplings, implying large ontogenetic differences in host tolerance to mite galling. We also found a significant negative correlation between canopy tree radial increment growth and levels of mite galling. Increased galling levels and higher physiological susceptibility in older canopy trees thus suggest that gall-inducing mites may be major drivers of “age-dependent” reductions in the physiological performance and growth of older trees.

Sublethal Effects of Bacillus thuringiensis Berliner subsp. kurstaki on Lymantria dispar (Lepidoptera: Lymantriidae) and the Tachinid Parasitoid Compsilura concinnata (Diptera: Tachinidae)

Abstract Parasitoid-pathogen interactions were examined using gypsy moth, Lymantria dispar (L.), Bacillus thuringiensis Berliner, and Compsilura concinnata (Meigen). The objectives of this study were to quantify effects of sublethal doses of Bacillus thuringiensis (Bt) force-fed to gypsy moths and to determine if sublethal doses of Bt affected host acceptance and suitability of gypsy moth for C. concinnata. Gypsy moths were minimally affected by sublethal doses of Bt; development of fourth instar was delayed, and male pupal mass reduced. Compsilura concinnata preferentially attacked and had higher superparasitism on noninfected hosts than on Bt-treated larvae. Exposure of gypsy moth to both sublethal doses of Bt and parasitoids reduced percentage parasitism and host larval survivorship. Effects on C. concinnata development varied with host superparasitism status. Parasitoids in Bt-treated, superparasitized gypsy moths had shorter larval development times and smaller pupal masses than parasitoids in untreated larvae, while parasitoids in singly parasitized larvae had larger pupal masses than those in superparasitized larvae. Timing of Bt infection relative to parasitism is a factor in gypsy moth mortality, but not in parasitoid potential fecundity.