Robert C. Venette

Invasions by Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in the Western Hemisphere: implications for South America

The multicolored Asian lady beetle, Harmonia axyridis (Pallas), native to Asia, has recently been detected in South America after successfully invading North America and Europe. This coccinellid is a voracious predator; therefore, it is popular and effective in biological control. Unfortunately, H. axyridis also has associated adverse impacts (i.e., as a household pest, pest of fruit production, and threat to non-target organisms). To predict the potential geographic extent of impacts of H. axyridis in South America we review the history of its invasion in the Western Hemisphere and address various factors critical to the future invasion (i.e., arrival, establishment, and spread) of new areas of South America. The likelihood of continued introductions (i.e., arrival) of H. axyridis to South America seems high, due to its popularity as a biological control agent and through accidental introductions. Establishment also seems likely in broad regions of South America. Climate matching with the native range suggested that much of southern South America may be suitable for establishment. In contrast, habitat matching with the native range suggested that northern South America may be more suitable. In addition, prey availability should not limit establishment of this predator. Once established, H. axyridis seems likely to spread by flight and human-assisted means. Overall, the invasion of H. axyridis over broad areas in South America seems likely.

Cold Hardiness of Winter-Acclimated Drosophila suzukii (Diptera: Drosophilidae) Adults

ABSTRACT Drosophila suzukii Matsumura, often called spotted wing drosophila, is an exotic vinegar fly that is native to Southeast Asia and was first detected in the continental United States in 2008. Previous modeling studies have suggested that D. suzukii might not survive in portions of the northern United States or southern Canada due to the effects of cold. As a result, we measured two aspects of insect cold tolerance, the supercooling point and lower lethal temperature, for D. suzukii summer-morph pupae and adults and winter-morph adults. Supercooling points were compared to adults of Drosophila melanogaster Meigen. The lower lethal temperature of D. suzukii winter-morph adults was significantly colder than that for D. suzukii summer-morph adults, while supercooling points of D. suzukii winter-morph adults were actually warmer than that for D. suzukii summer-morph adults and pupae. D. suzukii summer-morph adult supercooling points were not significantly different than those for D. melanogaster adults. These measures indicate that D. suzukii is a chill intolerant insect, and winter-morph adults are the most cold-tolerant life stage. These results can be used to improve predictions of where D. suzukii might be able to establish overwintering populations and cause extensive damage to spring fruit crops.

Cold Hardiness of Helicoverpa zea (Lepidoptera: Noctuidae) Pupae

ABSTRACT An insects cold hardiness affects its potential to overwinter and outbreak in different geographic regions. In this study, we characterized the response of Helicoverpa zea (Boddie) pupae to low temperatures by using controlled laboratory measurements of supercooling point (SCP), lower lethal temperature (LT50), and lower lethal time (LLTime). The impact of diapause, acclimation, and sex on the cold hardiness of the pupae also were evaluated. Sex did not significantly affect the SCP, LT50, or LLTime. However, the mean SCP of diapausing pupae (-19.3°C) was significantly lower than nondiapausing pupae (-16.4°C). Acclimation of nondiapausing pupae to constant temperatures from 10 to 20°C before supercooling also produced a significantly lower SCP than nondiapausing pupae held at 25°C. The LT50s of nondiapausing and diapausing were not significantly different, but confirmed that H. zea pupae are chill-intolerant because these lethal temperatures are warmer than the corresponding mean SCPs. Diapausing pupae survived longer than nondiapausing pupae at the same, constant, cold temperatures, a finding consistent with the SCP results. Both of these results suggest enhanced cold hardiness in diapausing pupae. When laboratory results were compared with field temperatures and observed distributions of H. zea in the contiguous United States, the laboratory results corroborated what is currently perceived to be the northern overwintering limit of H. zea; approximately the 40th parallel. Moreover, our research showed that areas north of this limit are lethal to overwintering pupae not because of low temperature extremes, but rather the length of time spent at near-zero temperatures.

Cold tolerance of Halyomorpha halys (Hemiptera: Pentatomidae) across geographic and temporal scales

Abstract The brown marmorated stink bug, Halyomorpha halys (Stål), is native to eastern Asia and is presently invading North America. Little is known about the exposure to and effects of winter temperatures in newly invaded regions on H. halys. The overwintering habitats that this species utilizes vary greatly in their thermal buffering capacity. They naturally overwinter in aggregations beneath loose bark on trees and in cliff outcroppings, but will also commonly aggregate in buildings. Effects of cold temperatures such as mortality and freezing have yet to be quantified in the invading population. We report that H. halys is chill intolerant (i.e., dies before reaching its freezing point), and that the degree of cold tolerance of populations in North America differs by season, sex, and acclimation location. The mean winter supercooling point (± SEM) of individuals acclimated in Minnesota was –17.06°C ± 0.13 and in Virginia was –13.90°C ± 0.09. By using laboratory assays of lower lethal temperatures and ambient air temperature records, we accurately forecasted mortality for field experiments in Minnesota and Virginia. Temperature refugia provided by human-built structures are likely crucial for overwintering survival during atypically cold winters and possibly contribute to the northern geographic range expansion of this economically damaging insect in the temperate climates of North America.

Effect of Temperature on Development and Population Parameters of Copitarsia decolora (Lepidoptera: Noctuidae)

Abstract The objective of this study was to evaluate the effect of temperature on survival, development, and reproduction of Copitarsia decolora. Both linear and nonlinear models were used to model temperature-dependent development and population growth for C. decolora reared on asparagus and artificial diet. We used @Risk Software to bootstrap model parameters so that variability in observations could be incorporated into model predictions. C. decolora eggs required ≈69 DD to complete development with a base temperature of 7.8°C. C. decolora developed through four to six instars depending on temperature and food source. Development of larvae from neonate through prepupa required 341.4 DD above a base of 7.3°C on asparagus, whereas 254.5 DD were needed on artificial diet, where the base temperature was 7.7°C. Pupae required ≈236 DD (base temperature 8.2–8.4°C) to develop when reared on asparagus or artificial diet. Female moths laid significantly more eggs at 14.6 and 20.1°C than at higher or lower temperatures. Survival of individuals to the adult stage increased from 71% at 9.7°C to 93% at 24.9°C. Survival fell off rapidly to 25% at 29.5°C. The generation time was the shortest at 29.5°C; however, only 25% of females survived to the adult stage, fecundity was low, and only 53% of the eggs hatched. The capacity for increase, rc, was low at 9.7°C, peaked at 25.7°C, and declined as temperature increased. We estimated that populations on asparagus would not develop at temperatures >31.3°C or <6.9°C. We show the importance of estimating a range of values for base temperature and degree-days by conducting a preliminary pathway analysis that incorporates the effect of temperature on egg hatch.

Agrilus auroguttatus (Coleoptera: Buprestidae) Seasonal Development within Quercus agrifolia (Fagales: Fagaceae) in Southern California

ABSTRACT We investigated seasonal development of the goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), and physical conditions of the phloem within a preferred host species, coast live oak, Quercus agrifolia Née. We sampled infested trees on a monthly basis at two sites in southern California throughout 2011. Measurements of an exposed portion of the head capsule, the peristoma, indicated that there were four larval instars. Pupae and teneral or mature adults were found within trees from April through August. Adults were captured in flight between May and mid-October, with peak flight from July through August. Within-tree A. auroguttatus prepupal mortality did not differ between sites and increased significantly from 3 ± 3% in January to 36 ± 9% in March (mean ± SE). Prepupae were present in trees throughout most of the year, which made it difficult to determine generation time; it was likely 1 yr for the majority of individuals, and possibly longer or shorter than 1 yr for others. Seasonal A. auroguttatus development, according to within-tree development and adult trap catch, was apparently 2 mo ahead at one site, which had a greater past and current level of A. auroguttatus infestation compared with the other. There was also evidence at the more severely infested site that within-tree A. auroguttatus population densities were positively related to proportion of dying phloem tissue. This suggested that the level of current infestation affected host tree condition, or that dying tissue was more suitable for larval development.

Acceptance and suitability of novel trees for Orthotomicus erosus, an exotic bark beetle in North America

To predict whether an herbivorous pest insect will establish in a new area, the potential host plants must be known. For invading bark beetles, adults must recognize and accept trees suitable for larval development. The preference-performance hypothesis predicts that adults will select host species that maximize the fitness of their offspring. We tested five species of North American conifers and one angiosperm for adult acceptance and suitability for reproduction of the Mediterranean pine engraver, Orthotomicus erosus (Wollaston). Red pine, Pinus resinosa Aiton, and white spruce, Picea glauca (Moench) Voss, were accepted by adult beetles and suitable for reproduction to the extent of adult replacement. Others, such as balsam fir, Abies balsamea (L.) Mill., eastern hemlock, Tsuga canagensis (L.) Carrière, and tamarack, Larix laricina (Du Roi) Koch, were acceptable but unsuitable. The presence of tree species that are acceptable to adults but unsuitable for reproduction may affect the ability of O. erosus to establish across North America.

Colonization behaviors of mountain pine beetle on novel hosts: Implications for range expansion into northeastern North America

As climates change, thermal limits may no longer constrain some native herbivores within their historical ranges. The mountain pine beetle, Dendroctonus ponderosae Hopkins, is a tree-killing bark beetle native to western North America that is currently expanding its range. Continued eastward expansion through the newly invaded and novel jack pine (Pinus banksiana Lamb.) trees of the Canadian boreal forest could result in exposure of several species of novel potential host pines common in northeastern North America to this oligophagous herbivore. Due to the tightly co-evolved relationship between mountain pine beetle and western pine hosts, in which the insect utilizes the defensive chemistry of the host to stimulate mass attacks, we hypothesized that lack of co-evolutionary association would affect the host attraction and acceptance behaviors of this insect among novel hosts, particularly those with little known historical association with an aggressive stem-infesting insect. We studied how beetle behavior differed among the various stages of colonization on newly cut logs of four novel potential pine host species; jack, red (P. resinosa Ait.), eastern white (P. strobus L.) and Scots (P. sylvestris L.) pines, as well as two historical hosts, ponderosa (P. ponderosa Dougl. ex. Laws. var. scopulorum Engelm.) and lodgepole (P. contorta Dougl. var. latifolia Engelm.) pines. Overall, we found that beetle colonization behaviors at each stage in the colonization process differ between pine hosts, likely due to differing chemical and physical bark traits. Pines without co-evolved constitutive defenses against mountain pine beetle exhibited reduced amounts of defensive monoterpenoid chemicals; however, such patterns also reduced beetle attraction and colonization. Neither chemical nor physical defenses fully defended trees against the various stages of host procurement that can result in tree colonization and death.

Sexing live mountain pine beetles Dendroctonus ponderosae: refinement of a behavioral method for Dendroctonus spp.

Members of the genus Dendroctonus (Coleoptera: Curculionidae, Scolytinae) are some of the most aggressive tree-killing bark beetles in the world. As such, much research on this genus has been undertaken to understand the factors that affect the population dynamics of these insects (Six & Bracewell, 2015; Aukema et al., 2016). Despite biome-level ecological impacts of the most aggressive members of this genus when at outbreak levels, the flight periods of many temperate species are constrained to just a few weeks of peak emergence during which beetles locate and procure hosts via pheromone-mediated mass attacks (Rudinsky, 1962; Raffa, 2001; Bentz et al., 2014). Females initiate boring into a host. Thus, for many manipulative laboratory and field experiments assessing reproduction or host selection, the ability to quickly and accurately determine the sex of live insects is required. Sexual dimorphism on the frons and pronotum is present in some species ofDendroctonus, most prominently in those species closely related to the southern pine beetle (Dendroctonus frontalis Zimmermann) (Wood, 1982), and provide varying degrees of accuracy in determination (Osgood & Clark, 1963; Tate & Bedard, 1967). The only consistently 100% accurate method of sex determination via secondary characters for Dendroctonus spp. requires examination of adults for the presence of a highly sclerotized plectrum on the seventh abdominal tergite (Lyon, 1958; Safranyik & Carroll, 2006). This plectrum is used for stridulation by males but absent in females. This morphological character is highly accurate (Lyon, 1958; Jantz & Johnsey, 1964; Godbee & Franklin, 1978), but can pose challenges when working with live insects (Tate & Bedard, 1967). For example, female mountain pine beetles (Dendroctonus ponderosae Hopkins) tend to draw their abdomens tight against the elytra when prodded. Squeezing the abdomen or manipulating its position with a metal probe under a dissecting microscope (McCambridge, 1962) can extend handling times and result in harm to the insect (Godbee & Franklin, 1978). Morphological examinations remain a popular technique, however, and work reliably when executed properly. Several authors have tested the efficacy of stridulatory behavior as a potential method for sex determination of live Dendroctonus beetles (Table 1). When disturbed, males will use stridulation to produce predominantly simple ‘stress’ chirps that are characterized by rapid short bursts (McCambridge, 1962; Michael & Rudinsky, 1972; Fleming et al., 2013). Chirps are produced as males move the plectrum against the pars stridens on the underside of the elytra (Hopkins, 1909; Michael & Rudinsky, 1972). Female Dendroctonus spp. beetles are also able to stridulate, using a different stridulatory apparatus, but their short, simple chirps, characterized by a low sound pulse rate, are easily differentiated from the rapid chirping and higher sound pulse rates of males (Barr, 1969; Rudinsky & Michael, 1973; Yturralde & Hofstetter, 2015). Sonic emissions of female Dendroctonus spp. are typically restricted to courtship behaviors, though a stress response has been detected in the red turpentine beetle (Dendroctonus valens LeConte) and the larger Mexican pine beetle (Dendroctonus approximatus Dietz) (Ryker & Rudinsky, 1976a; Yturralde & Hofstetter, 2015). The ability to chirp likely confers reproductive advantage to the joining sex, as this trait has been independently gained in both Dendroctonus and Ips (Barr, 1969; Lewis & Cane, 1990), and is conserved amongmales acrossDendroctonus spp. (Ryker, 1988). Though audible observations of stridulation can be useful for sexing adults of Dendroctonus spp., some error is *Correspondence: DerekW. Rosenberger, Department of Entomology, University ofMinnesota, 1980 Folwell Avenue, St. Paul, MN 55108, USA. E-mail: rose0675@umn.edu

Goldspotted oak borer effects on tree health and colonization patterns at six newly-established sites

Newly‐established populations of invasive wood‐inhabiting insects provide an opportunity for the study of invasion dynamics and for collecting information to improve management options for these cryptic species. From 2011 to 2013, we studied the dynamics of the goldspotted oak borer Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), a new pest of oaks in southern California, at six sites that had been colonized recently. At all sites, the percentage of coast live oaks Quercus agrifolia Née, colonized by A. auroguttatus increased between 2011 (6–33%) and 2013 (23–40%), although beetle densities did not grow rapidly at most sites. From 2011 to 2013, there were minor changes in signs and symptoms of A. auroguttatus infestation (adult emergence holes, bark staining, and evidence of woodpecker foraging), except at one site where an outbreak occurred. At some sites, noticeable negative changes in oak crown health occurred 1 year prior to positive A. auroguttatus population growth. Among sites, most of the A. auroguttatus population density (66–93%) was produced by a small number of heavily‐infested trees (= brood trees). Early identification and removal of brood trees in newly‐invaded areas could slow the growth of A. auroguttatus populations.