Predicted Impact of an Exotic Generalist Predator on Monarch Butterfly (Lepidoptera: Nymphalidae) Populations: A Quantitative Risk Assessment

The multicolored Asian lady beetle, Harmonia axyridis (Pallas), was recently identified as a potential hazard to monarch butterflies, Danaus plexippus (L.). A quantitative risk assessment for the potential impact of H. axyridis on D. plexippus in Minnesota corn and soybean fields was developed using risk analysis software. This assessment considered a potential worst-case scenario for the impact of H. axyridis on D. plexippus. Habitat-specific recruitment of D. plexippus eggs was determined empirically. Subsequently, simulated abundance of D. plexippus in each habitat was reduced by two classes of stage-specific mortality: predation by H. axyridis and causes other than H. axyridis. Predation was modeled as a function of D. plexippus exposure to H. axyridis, and predation rate of D. plexippus by H. axyridis. Exposure and subsequent risk varied considerably by habitat, with a low risk of H. axyridis adversely affecting D. plexippus populations developing in corn fields, but a moderate to high risk in soybean fields. Predicted rates of D. plexippus mortality attributable to H. axyridis were greater in soybean compared to corn fields, possibly due to the numerical response of H. axyridis to soybean aphid, Aphis glycines Matsumura. This study demonstrates that H. axyridis has the potential to have a strong adverse impact on D. plexippus populations. However, the likelihood of occurrence for this worst-case scenario remains uncertain. To evaluate the landscape-level risk of H. axyridis impacting D. plexippus, further data on recruitment of D. plexippus in other habitats and exposure estimates specific to additional habitats are needed.     

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.     

Walking Response of the Mediterranean Pine Engraver, <Emphasis Type="Italic">Orthotomicus erosus</Emphasis>, to Novel Plant Odors in a Laboratory Olfactometer

When an herbivorous insect enters a new geographic area, it will select host plants based on short and long distance cues. A conifer-feeding bark beetle that has been recently introduced to North America, the Mediterranean pine engraver, Orthotomicus erosus (Wollaston), has a potentially wide host range, especially among members of the Pinaceae. The long-distance response of the beetles to tree odors may be a key feature of the mechanism of host recognition and selection. We used a laboratory olfactometer to study the walking response of 1,440 O. erosus to odor cues from the bark and phloem of six North American tree species. The beetle moved toward the angiosperm non-host Betula papyrifera more than would be expected by chance, but had a neutral response to odors of two tree species that support reproduction and three species that do not. These results suggest that tree odors alone may not be adequate for O. erosus to recognize novel hosts.     

Acceptance and suitability of novel trees for <Emphasis Type="Italic">Orthotomicus erosus</Emphasis>, 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.     

Host‐mediated shift in the cold tolerance of an invasive insect

While many insects cannot survive the formation of ice within their bodies, a few species can. On the evolutionary continuum from freeze‐intolerant (i.e., freeze‐avoidant) to freeze‐tolerant insects, intermediates likely exist that can withstand some ice formation, but not enough to be considered fully freeze tolerant. Theory suggests that freeze tolerance should be favored over freeze avoidance among individuals that have low relative fitness before exposure to cold. For phytophagous insects, numerous studies have shown that host (or nutrition) can affect fitness and cold‐tolerance strategy, respectively, but no research has investigated whether changes in fitness caused by different hosts of polyphagous species could lead to systematic changes in cold‐tolerance strategy. We tested this relationship with the invasive, polyphagous moth, Epiphyas postvittana (Walker). Host affected components of fitness, such as larval survivorship rates, pupal mass, and immature developmental times. Host species also caused a dramatic change in survival of late‐instar larvae after the onset of freezing—from less than 8% to nearly 80%. The degree of survival after the onset of freezing was inversely correlated with components of fitness in the absence of cold exposure. Our research is the first empirical evidence of an evolutionary mechanism that may drive changes in cold‐tolerance strategies. Additionally, characterizing the effects of host plants on insect cold tolerance will enhance forecasts of invasive species dynamics, especially under climate change.     

Sublethal effects of subzero temperatures on the light brown apple moth,Epiphyas postvittana: fitness costs in response to partial freezing

Population responses to envir on mental extremes often dictate the bounds to species' distributions. However, population dynamics at, or near, those range limits may also be affected by sublethal effects. We exposed late instars and pupae of an invasive leafroller, Epiphyaspostvittana (Walker)(Lepidoptera: Tortricidae), to cold temperatures and measured the effects of exposure on subsequent survivorship, development, and reproduction. Cold temperature was applied as acute exposure to -10 °C (a low, but not immediately lethal temperature for this species) or the onset of freezing (the peak of the supercooling point exotherm). Survival was defined as the ability to successfully eclose as an adult. We measured immature development times, pupal mass, and adult longevity as proxies of fitness in survivors. Additionally, surviving insects were mated with individuals that had not been exposed to cold to measure fertility. There was no difference between the proportion of larvae or pupae that survived acute exposure to -10 °C and those exposed to the control temperature. Approximately 17% of larvae and 8% of pupae survived brief periods with internal ice formation and continued development to become reproductively viable adults. Importantly, surviving the onset of freezing came with significant fitness costs but not to exposure to -10 °C;most insects that survived partial freezing had lower fertility and shorter adult lifespans than either the -10 °C or control group. These results are discussed within the context of forecasting invasive in sect distributions.     

Suitability of native and ornamental oak species in California for Agrilus auroguttatus

Goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is a new invasive species in southern California, USA. The extent of the host range of this insect is not known, but this knowledge will have a major impact on assessment of the risks that this pest poses to oaks [Quercus spp. (Fagaceae)]. We conducted laboratory tests to determine the potential suitability of native and ornamental oak species for larvae and adults of A. auroguttatus. We infested 179 cut logs (from 163 different trees) with eggs or larvae, measured neonate survival and, after 5 months, counted feeding galleries, and noted the proportion of galleries with late instars. Initial larval survival was generally high when larvae penetrated the phloem (range: 62–98% among oak species), and low by the time larvae began to feed at the phloem/xylem interface (range: 0–25% among oak species). The majority of larvae that established a visible feeding gallery survived to the fourth instar (total of 73% for all oak species). Larval galleries were established with greater frequency in red oaks (Section Lobatae) compared with other oaks (19 vs. 7 or 4%). All red oaks tested (Q. agrifolia Née, Q. kelloggii Newberry, and Q. wislizeni A. DC.) were likely suitable hosts for larvae. Larvae were apparently able to feed on some of the other oaks (Q. chrysolepis Leibmann, Q. suber L., Q. lobata Née, and Q. douglasii Hook & Arn), although it remains unclear whether these species would be preferred hosts under natural conditions. Adult longevity and fecundity varied little by species of oak foliage fed to adults. The host range of A. auroguttatus is likely limited by suitability of oak species for the larval rather than the adult life stage. Results support published field observations that red oaks are more suitable hosts than white oaks.