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Coneworms, Dioryctria Zeller (Lepidoptera: Pyralidae), are destructive pests of conifers across North America, and members of several different species groups present significant pestmanagement challenges in conifer seed orchards. Dioryctria abietivorella Grote (abietella group) is the most pestiferous Dioryctria species in Canada. Despite this status, control tactics are currently limited to broad-spectrum pesticides that threaten non-target species and may result in pesticide resistance. The development of integrated pest management programs targeting Dioryctria species will benefit from a conceptual framework on which to base future research. To create this structure, we review the systematics, evolutionary ecology, and management of cone-feeding North American Dioryctria species. Current research suggests that many species boundaries are in need of further revision. Major gaps in our understanding of Dioryctria ecology impede the development of integrated pest management tactics. For example, host-generated semiochemicals are important in Dioryctria reproduction, although the uses of these cues in host-finding and host acceptance remain unknown. Future research should identify factors that mediate population distribution at landscape (e.g., migration), local (e.g., feeding stimulants), and temporal (e.g., development thresholds) scales.
Systematics & Morphology / Systématique et morphologie
Aphids of the genus Tuberculatus Mordvilko feed on Fagaceae trees and exhibit various interactions with ants, ranging from non-attendance to intermediate or close associations. Despite possession of fully developed wings, two ant-attended species, Tuberculatus quercicola (Matsumura) and Tuberculatus sp. A, exhibited extremely low dispersal. I examined the correlation between wing loading (ratio of body volume to wing area) and ant associations in 20 species of Tuberculatus. Based on a 1317 bp sequence in two mitochondrial regions, cytochrome oxidase I (COI) and NADH dehydrogenase subunit 1 (ND1), phylogenetic trees were reconstructed by neighbor-joining (NJ), most parsimony (MP), maximum likelihood (ML), and Bayesian analyses. AU phylogenetic trees showed that mutualistic interactions with ants have evolved in Tuberculatus at least five times. Comparative analyses based on the NJ, MP, and ML trees showed that increase in wing loading is correlated with ant associations, suggesting that ant-attended aphids have allocated more resources to their bodies than to their wings, resulting in lowered dispersal.
We identified species of mites phoretically associated with mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae), collected from bolts of lodgepole pine, Pinus contorta Douglas ex Louden (Pinaceae), and pheromone-baited traps in northwestern Alberta, Canada. Mite load and species composition were compared between beetle sexes and with beetle emergence time and estimated body size. The vast majority of mites associated with D. ponderosae in Alberta belonged to three species: Proctolaelaps subcorticalis Lindquist (Acari: Mesostigmata: Melicharidae), Histiogaster arborsignis Woodring (Acari: Astigmatina: Acaridae), and Tarsonemus ips Lindquist (Acari: Prostigmata: Tarsonemidae). There was no difference in mite loads on male and female beetles recovered from bolts in the laboratory and those from pheromone-baited traps in the field. More mites were found on larger beetles in the laboratory, but only T. ips showed this pattern on field-trapped beetles. There was no relationship between total mite load or load by mite species and beetle emergence time in the laboratory, but total mite load on field-trapped beetles decreased over the collecting season (10 June – 3 September 2009) at five collection locations (Grovedale, Blueberry Mountain, Hythe, Evergreen Park, and Glenleslie). This study is the first to document the assemblage of phoretic mites on D. ponderosae in Alberta and will help to direct future research on their interactions.
Where winters are severe, aphids reproduce parthenogenetically and viviparously in summer, switch to sexual reproduction in late summer, and produce winter-hardy eggs by the end of the season. The role of day length and temperature in initiating seasonal changes from parthenogenetic to sexual reproduction by pea aphids, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), are described and the selection pressures that affect the timing of this transition are investigated. Over four seasons, a pea aphid clone was sampled from field cages through late summer in southern Manitoba, Canada, and reared in the laboratory to determine the phenotypes of progeny produced as the season progressed. The timing of transitions from one phenotype to another under natural day length and temperature, and the critical day lengths that caused the transitions, coincided with expectations from laboratory studies of photoperiodic responses. Males and mating females appeared later when the weather in August was warm than when it was cool. The timing of seasonal changes was adapted to minimize the physiological time to the end of the season, which maximized the number of asexual summer generations. Ambient temperature modulated the response to day length and fine-tuned the timing of sexual reproduction to adapt for annual variation in autumn weather.
Knowledge of the factors affecting host selection by herbivorous insects is essential to predictions of their distribution and abundance over landscapes. In the laboratory, we studied the oviposition preferences of two eruptive loopers (Lepidoptera: Geometridae) native to western Canada (western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), and phantom hemlock looper, Nepytia phantasmaria (Strecker)) for different species and condition of hosts. When offered a choice, phantom hemlock loopers laid nearly three times as many eggs on western hemlock, Tsuga heterophylla (Raf.) Sarg. (Pinaceae) as on either western redcedar, Thuja plicata Donn ex D. Don (Cupressaceae) or western white pine, Pinus monticola Douglas ex D. Don (Pinaceae). Western hemlock loopers were less specific, laying equal numbers of eggs on western hemlock and western redcedar, though fewer eggs were deposited on western white pine when compared with western hemlock. When offered western hemlock trees grown under different nutrient and shading regimes, phantom hemlock loopers preferred to oviposit on high nutrient hosts, irrespective of shading; western hemlock loopers exhibited a preference for high-nutrient hosts only if they were grown without shading. These patterns of host preference can be combined with information regarding forest composition to help quantify the conditional probability of western and phantom hemlock looper distibution and abundance.
Biodiversity & Evolution / Biodiversité et evolution
Evidence indicates low levels of hybridization in nature between the apple maggot (AM), Rhagoletis pomonella (Walsh), and snowberry maggot (SB), Rhagoletis zephyria Snow, sibling species in the R. pomonella complex. We determined the effects of AM and SB pairings on mating frequencies and production of hybrid offspring in the laboratory. Mating frequency was lowest in SB female × AM male pairings, higher in AM female × SB male and AM female × AM male pairings, and highest in SB female × SB male pairings. A greater percentage of AM female × AM male pairs produced offspring (puparia) than did AM female × SB male and SB female × AM male pairs, and a greater percentage of AM female × SB male pairs produced puparia than did SB female × AM male pairs. Male or female F1 hybrids backcrossed with AM males and with other F1 hybrids were fertile. Results suggest most R. pomonella × R. zephyria hybrids found in nature are the result of R. zephyria males mating with R. pomonella females, with few from reciprocal matings. If true, this asymmetry could lower the incidence of hybridization in nature.
Abundance, persistence, and variability of populations of Macrosiphum euphorbiae (Thomas), Myzus persicae (Sulzer), and Aphis nasturtii Kaltenbach (Hemiptera: Aphididae) in potato plots for intervals of 58 years (n = 1), 29 years (n = 2), 19–20 years (n = 3), and 9–10 years (n = 6) were compared. The abundance of M. euphorbiae showed no trend among decades and varied 2.4-fold, whereas that of M. persicae and A. nasturtii declined and showed 54-fold and 3700-fold variation, respectively. All three aphid species persisted through the first five decades and M. euphorbiae also persisted through the sixth (last) decade, but M. persicae and A. nasturtii failed to persist for 1 and 3 years of the last decade, respectively. Population variability (a proportion between 0 and 1) measured over a 58-year interval was high: 0.585 for M. euphorbiae, 0.771 for M. persicae, and 0.830 for A. nasturtii. During the first three but not the last three decades, population variability increased with sampling interval, owing to dramatic declines in abundance for M. persicae and A. nasturtii and one stable decade for M. euphorbiae, but no evidence of a more-time — more-variation effect was detected. Persistence was not related to population variability, but declined with abundance. Populations did not reach equilibrium, because of declining abundance for M. persicae and A. nasturtii and changes in population variability from decade to decade for M. euphorbiae. Populations of M. persicae and A. nasturtii from this crop monoculture were less stable than previously studied natural populations of a native aphid species. In contrast, the population of M. euphorbiae, a native species, had variability in a potato crop similar to that of the previously studied native species. The high population variability of M. persicae and A. nasturtii may be associated with their status as introduced species. The dynamic and species-specific characteristics of population variability require that interspecific comparisons be considered cautiously.
We report a two-step method to rear three leafhopper species, Erythroneura elegantula Osborn, Erythroneura vitis (Harris), and Erythroneura ziczac Walsh, for experimental purposes on grapevines. The first step involves rearing adults on grapevines for reproduction, oviposition, and egg development. The second step involves rearing nymphs on isolated leaves placed in Petri dishes lined with agar. No mortality was observed and adults emerged in about three weeks. The three Erythroneura species were reared for 10 consecutive generations with minimal resources.