Ovarian development of Agrilus planipennis: effects of age and mating status and influence on attraction to host volatiles

Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a major pest of ash trees, Fraxinus spp. (Oleaceae), in North America. This study investigated the timing of reproductive development in female beetles and the influence of female reproductive maturity on attraction to host volatiles. Based on dissections of females of increasing age, females with access to males for mating, and thus presumed mated, developed mature eggs only after 18–24 days. In contrast, female beetles reared without access to males, and thus unmated, did not develop mature eggs at any age. Chemical analysis of cuticular hydrocarbons detected the contact sex pheromone, 9‐methyl‐pentacosane, in cohorts of females which were 8–9 days old and older, supporting previous research that this compound signals sexual maturity to males. Results from field‐trapping bioassays demonstrated that stage of female reproductive maturity influenced their attraction to host volatiles: females caught on traps baited with foliar volatiles contained eggs and ovarioles that were significantly less developed than those on traps baited with bark sesquiterpenes. However, our results revealed that females with immature stages of ovarioles and undeveloped eggs, such as those observed in unmated females, were rarely ever caught on traps baited with either of the host volatile lures. Further research on host compounds attractive to immature females is critical for early detection and possible control of A. planipennis populations during the extended pre‐oviposition period.     

Flight Performance of <Emphasis Type="Italic">Agrilus planipennis</Emphasis> (Coleoptera: Buprestidae) on a Flight Mill and in Free Flight

Computer-monitored flight mills were used to record the flight performance of the emerald ash borer, Agrilus planipennis Fairmaire. Flight performance of fed and unfed, and mated and unmated beetles of both sexes were recorded and compared. Mated females flew further per day and longer than unmated females or males. Mated females that were allowed to feed between flight periods flew an average of 1.3 km/day for four days; 10% flew more than 7 km/day. Measurements of free-flight speed using a mirror and a high-speed camera were used to calibrate the flight mill results, permitting absolute estimates of flight performance to be made. Free-flight speeds were approximately three times the speeds recorded by the flight mills. The median corrected distance flown by mated females was >3 km with 20% flying >10 km and 1% flying >20 km. The flight performance of mated females suggests a considerable capacity for range expansion by this invasive species. The implications for quarantine and control are discussed.     

Is success in detection of Agrilus planipennis related to forest edges?

The emerald ash borer (Agrilus planipennis) is a destructive invasive beetle that has caused mortality of millions of Fraxinus spp. trees in North America. The extended interval between insect establishment, detection and management has allowed this pest to spread over large parts of North America. Artificial purple canopy traps are currently used in national detection surveys for this beetle. The effectiveness of purple canopy traps at low‐to‐moderate A. planipennis population densities in relation to road proximity was evaluated in 2013 and 2014. Transects of traps were established at set distances from roads in northern Michigan near an isolated A. planipennis infestation. It was hypothesized that trap effectiveness is influenced by road proximity, and that traps placed closer to roads were more likely to detect A. planipennis. A significant relationship was established between the mean number of A. planipennis captured on traps and road proximity (nearness), while no significant relationship was observed between detection success and road proximity. These findings suggest establishing traps further from roads (which can be less economically efficient) provides no greater likelihood of detection than establishing traps on or near the road edge. Basal area of non‐ash and ash species, beetle population density, vigour rating, ash tree species and sampling duration were shown to significantly influence the number of A. planipennis captured on traps.     

Sex Differences in Mate Preference Between Two Hybridizing Species of Poeciliid Fish

When hybridization between two species in secondary contact is costly, natural selection should favor pre‐mating isolation barriers. The invasive Gambusia affinis has been introduced to habitats of a closely related species, the endangered Gambusia nobilis. Although other Gambusia species readily hybridize in secondary contact, previous studies in this system found low abundance of hybrids in sympatry. To examine whether hybridization is limited by behavioral pre‐mating isolation that may have evolved in allopatry, I examined each species’ mating preferences using individuals from allopatric populations in male and female visual/olfactory association preference tests as well as open mating tests with and without male–male competition. Gambusia affinis and G. nobilis males had significant association preference for conspecific females in visual/olfactory tests. Only G. nobilis females had statistically significant preference for conspecific males. In open mating tests, males of both species had lower chase times overall when in competition, but there was no difference in number of copulation attempts. Males of both species had higher copulatory success rates with conspecific females when in competition, suggesting females may exert some control over copulation success of males. These results suggest that there are differences in mating preferences between these species. This mate choice may act as a pre‐mating isolating barrier to reduce hybridization in sympatry, a proposed threat to the endangered G. nobilis.     

A new forest pest in Europe: a review of Emerald ash borer (Agrilus planipennis) invasion

In this publication, we review the biology, ecology, invasion history, impacts and management options of Emerald ash borer (EAB) Agrilus plannipennis, with a particular focus on its invasion in Europe. Agrilus planipennis (EAB) is a wood‐boring beetle native to East Asia. Having caused massive damages on ash species in North America in the last decades, it was first recorded in Europe in 2003 in Russia (Moscow). All ash (Fraxinus) species native to Europe and North America are known to be susceptible to EAB attacks, which cause high tree mortality even among formerly healthy trees. Recorded expansion rates are between 2.5 and 80 km/year in North America and between 13 and 41 km/year in European Russia. Given current expansion rates, EAB is expected to reach Central Europe within 15–20 years. A combination of mechanical, biological and chemical control and phytosanitary measures may reduce its impact, which nevertheless most likely will be substantial. There is an urgent need to identify native enemies in Europe, to test suitable biocontrol agents and to develop early detection and management measures. Although it is obvious that EAB will become a major pest in Europe, early and dedicated response will likely be able to reduce the level of ash mortality, and thus improve the opportunity for long‐term survival of ash as an important component in European forests.     

Visually Mediated ‘Paratrooper Copulations’ in the Mating Behavior of <Emphasis Type="Italic">Agrilus planipennis</Emphasis> (Coleoptera: Buprestidae), a Highly Destructive Invasive Pest of North American Ash Trees

The emerald ash borer, Agrilus planipennis, is a serious invasive pest of North American ash (Fraxinus) trees. In captivity, mating is initiated by beetles at least 10 days old, and appears to be based simply on random contact with a member of the opposite sex. In the field, male A. planipennis search the tree during flight, and attempt to copulate with dead beetles of both sexes pinned to leaves, after descending rapidly straight down onto the pinned beetles from a height of from 30 to 100 cm. All evidence suggests that males find potential mates using visual cues. Equal numbers of feral males approach all ‘dummy’ beetles; however, considerably more time is spent attempting copulation with dead females rather than males, suggesting a contact chemical cue. Sticky traps prepared from dead, pinned EAB capture crawling insects as well as male A. planipennis, at a rate similar to that at which small purple sticky traps of similar overall area capture crawling insects and both sexes of feral EAB.     

Intended and unintended receivers of the male pheromones of the burying beetles Nicrophorus humator and Nicrophorus vespilloides

Male Nicrophorus beetles (Coleoptera: Silphidae) attract females through volatiles that are emitted at species‐specific times of day. Not only beetles of the opposite sex but also conspecific males are attracted. Another observation is the co‐attraction of congeners, a phenomenon that was shown in particular for Nicrophorus vespilloides Herbst, the smallest Nicrophorus species in Central Europe. In the current study, we identified the Nicrophorus humator Gleditsch male pheromone as methyl 4‐methyloctanoate through gas chromatography/mass spectrometry analysis. In field experiments, we tested and compared the attractiveness of synthetic analogs of the male pheromones of N. humator and N. vespilloides in baited pitfall traps. An asymmetric cross‐attraction to the synthetic male pheromones was observed, which is best explained by the skewed competitive relationship of the two species, with regard to the restricted availability of breeding resources. Nicrophorus humator is attracted by both its own male pheromone and by the pheromone of the smaller N. vespilloides, whereas N. vespilloides is almost exclusively attracted by its own male pheromone. The observed attraction of conspecific males of either species to male pheromone baits can be explained by both competition for females and competition for breeding resources.     

Mate Choice by Both Sexes Maintains Reproductive Isolation in a Species Flock of Pupfish (Cyprinodon spp) in the Bahamas

Female and male mate choices can reinforce reproductive isolation after sympatric speciation. Using a binary choice design, we examine the importance of visual cues in female mate choice in all three sympatric species of pupfish on San Salvador Island. We also examine the importance of olfactory cues in female choice of the hard‐shelled invertebrate specialist (Cyprinodon brontotheroides). We examine male mate choice in two of the three species, the scale eater (C. desquamator) and the detritivore (C. variegatus). Females of all three species use visual cues and prefer conspecific males. C. brontotheroides females do not use olfactory cues to discriminate between conspecific and heterospecific males. Males of C. desquamator and C. variegatus also preferentially court conspecific females. Thus, mutual mate choice, where both females and males exhibit mate choice, acts as a strong behavioral pre‐mating isolation mechanism in these sympatrically speciated pupfish.     

The role of species‐specific sensory cues in male responses to mating rivals in Drosophila melanogaster fruitflies

Complex sets of cues can be important in recognizing and responding to conspecific mating competitors and avoiding potentially costly heterospecific competitive interactions. Within Drosophila melanogaster, males can detect sensory inputs from conspecifics to assess the level of competition. They respond to rivals by significantly extending mating duration and gain significant fitness benefits from doing so. Here, we tested the idea that the multiple sensory cues used by D. melanogaster males to detect conspecifics also function to minimize “off‐target” responses to heterospecific males that they might encounter (Drosophila simulans, Drosophila yakuba, Drosophila pseudoobscura, or Drosophila virilis). Focal D. melanogaster males exposed to D. simulans or D. pseudoobscura subsequently increased mating duration, but to a lesser extent than following exposure to conspecific rivals. The magnitude of rivals’ responses expressed by D. melanogaster males did not align with genetic distance between species, and none of the sensory manipulations caused D. melanogaster to respond to males of all other species tested. However, when we removed or provided “false” sensory cues, D. melanogaster males became more likely to show increased mating duration responses to heterospecific males. We suggest that benefits of avoiding inaccurate assessment of the competitive environment may shape the evolution of recognition cues.     

Efficacy of the pheromone (3Z)‐lactone and the host kairomone (3Z)‐hexenol at detecting early infestation of the emerald ash borer,Agrilus planipennis

The invasive emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a major pest of ash trees, Fraxinus spp., in its introduced range in North America. Field studies were conducted to quantify the efficacy of traps baited with kairomone and pheromone lures for early detection of A. planipennis infestation. A trapping experiment demonstrated that green traps baited with the kairomone (3Z)‐hexenol detected at least one adult A. planipennis in 55.3% of plots with ‘nil to low’‐density infestations and in 100% of plots with ‘moderate to high’‐density A. planipennis infestations. Mean trap captures increased significantly with increasing infestation density. In terms of the optimal number of traps per plot, when one (3Z)‐hexenol‐baited trap was placed per plot, the trap detected populations in 62% of the plots with ‘low to moderate’‐density infestations through branch sampling. Detectability was increased to 82% when two traps were placed per plot. Finally, addition of female‐produced (3Z)‐lactone pheromone to traps significantly increased detection rates at both the trap and plot level, as compared with traps baited with the host volatile, (3Z)‐hexenol, alone (88 vs. 60%, respectively). Our results are the first to demonstrate the efficacy of baited green sticky traps for detecting low‐density A. planipennis infestations, particularly when the (3Z)‐lactone pheromone is used. This combination is therefore recommended for development of early‐detection protocols against A. planipennis.     

The magnitude of behavioral isolation is affected by characteristics of the mating community

Gene exchange between species occurs in areas of secondary contact, where two species have the opportunity to hybridize. If heterospecific males are more common than conspecific males, females will experience more encounters with males of other species. These encounters might increase the likelihood of heterospecific matings, and lead to the production of hybrid progeny. I studied the mating behavior of two pairs of sibling species endemic to Africa: Drosophila yakuba/Drosophila santomea and Drosophila simulans/Drosophila sechellia. Drosophila yakuba and D. simulans are cosmopolitan species widely distributed in the African continent, while D. santomea and D. sechellia are island endemics. These pairs of species hybridize in nature and have the potential to exchange genes in natural conditions. I used these two pairs of Drosophila species, and constructed mating communities of different size and different heterospecific:conspecific composition. I found that both the total number of potential mates and the relative frequency of conspecific versus heterospecific males affect female mating decisions in the cosmopolitan species but not in the island endemics. These results suggest that the population characteristics, in which mating occurs, may affect the magnitude of premating isolation. Community composition might thus facilitate, or impair, gene flow between species.     

Survey tools and demographic parameters of Slovakian Agrilus associated with beech and poplar

Woodborers in the Agrilus genus (Coleoptera: Buprestidae) pose high invasiveness risk as indicated by the recent invasion and continental spread of emerald ash borer, and the associated threat to ash resources in North America. In that context, development of detection tools for potentially invasive Agrilus spp. is a research priority. Experiments carried out in 2013 in Slovakian beech and poplar forests evaluated the attraction of multiple Agrilus species to green and purple sticky prism traps baited with various lures [blank, cubeb oil, (Z)‐3‐hexenol]. The two most abundant species were Agrilus viridis L. in beech (Fagus spp.) forest (146 adults, >95% of which were females) and Agrilus convexicollis Redtenbacher in poplar (Populus spp.) forest (158 adults, two‐thirds of them males). The two species exhibited opposite responses to color: purple traps attracted 2–3× more adult A. viridis than green traps, whereas most (>95%) specimens of A. convexicollis were captured on green traps. Volatile baits did not influence captures of adults for either species. The introduction and establishment of A. viridis in North America is of particular concern owing to its feeding niche (primary pest that can attack healthy trees), large body size, and high level of polyphagy (>10 genera of host trees). Additional experiments conducted in beech forests in 2014 found purple prism traps more attractive to female A. viridis than green prism traps, especially those baited with cubeb oil. No analysis was conducted for males because of their low abundance. Female A. viridis flew earlier in 2013 than in 2014, but neither their body size nor fecundity varied between years. In both years, large females had more eggs in their abdomen than small females, and the number of eggs steadily declined over time, which suggests that female A. viridis are reproductively mature at emergence.     

Latitudinal variation in body size of Agrilus planipennis and relationship with fecundity

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Reproductive interference by male Drosophila subobscura on female D. persimilis: A laboratory experiment

While females often reject courtship attempts by heterospecific males, reproductive interference by harassment from such males can nonetheless occur, potentially reducing female fitness. Such effects may be profound following a range expansion, when males from a new species may suddenly encounter (and perhaps even become abundant relative to) females of related native species. Drosophila subobscura recently invaded North America and may impact native species through reproductive interference and other processes. We test for the potential for reproductive interference by D. subobscura males on D. persimilis females in the laboratory. D. subobscura males aggressively copulated with D. persimilis females, including many females that exhibit rejection behaviors. Despite females attempting to dismount the males, the heterospecific copulations are on average longer than conspecific copulations, and females exhibit some reluctance to remate with conspecific males following this harassment. Females confined with both conspecific and heterospecific males produce fewer adult progeny than those with either conspecific males only or with conspecific males and distantly related D. simulans males that do not engage in female harassment. Overall, our results illustrate how reproductive interference by an invasive species can have negative effects on resident natural populations.     

Trapping of European buprestid beetles in oak forests using visual and olfactory cues

Trapping approaches developed for the emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), were adapted for trapping several European oak buprestid species. These approaches included the use of natural leaf surfaces as well as green and purple plastic in sticky trap designs. Plastic surfaces were incorporated into novel ‘branch‐trap’ designs that each presented two 5 × 9‐cm² rectangular surfaces on a cardboard structure wrapped around the leaves of a branch. We used visual adult Agrilus decoys in an attempt to evoke male mating approaches toward the traps. Our first experiment compared the attractiveness of visual characteristics of the surfaces of branch‐traps. The second looked at the effect on trap captures of adding semiochemical lures, including manuka oil, (Z)‐3‐hexen‐1‐ol, and (Z)‐9‐tricosene. In total, 1 962 buprestid specimens including 14 species from the genus Agrilus were caught on 178 traps in a 22‐day time‐span. Overall, the green plastic‐covered branch‐traps significantly out‐performed the other trap designs. We further found that the presence of an EAB visual decoy placed on the trap surface often increased captures on these green traps, but this effect was stronger for certain Agrilus species than for others. The visual decoy was particularly important for the most serious pest detected, Agrilus biguttatus Fabricius, which was captured 13 times on traps with decoys, but only once without a decoy. There were some small but significant effects of odor treatment on the capture of buprestids of two common species, Agrilus angustulus Illiger and Agrilus sulcicollis Lacordaire. There were also 141 Elateridae specimens on these traps, which were not influenced by trap type or decoys. The results suggest that small branch‐traps of this nature can provide a useful new tool for monitoring of buprestids, which have the potential to be further optimized with respect to visual and olfactory cues.     

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.     

Foliar nutrients explain goldspotted oak borer,Agrilus auroguttatus,adult feeding preference among four California oak species

Adults of the invasive goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), consumed foliar weight in no‐choice feeding tests of, in descending order, California black oak Quercus kelloggii Newb., Engelmann oak, Quercus engelmannii Greene, coast live oak, Quercus agrifolia Née, and canyon live oak, Quercus chrysolepis Liebm. (Fagaceae). Furthermore, significantly more foliar area was consumed of Q. kelloggii than of Q. chrysolepis. In dual‐choice feeding tests with isolated leaf disks, A. auroguttatus consumed significantly more foliar weight and area of Q. kelloggii relative to the other three oak species, and more foliar weight of Q. agrifolia than of Q. chrysolepis. In dual‐choice feeding tests with leaves on small branches, A. auroguttatus consumed more foliar weight of Q. kelloggii than of Q. engelmannii and Q. agrifolia. Thus, multiple experiments suggested that adults of A. auroguttatus preferred the foliage of Q. kelloggii over that of the other three oak species, and among the other three species they did not appear to have a strong feeding preference. Factor analysis reduced the quantities of 13 foliar nutrients into two new variables (factor 1 and factor 2). Factor 1 was weighted heavily on the quantities of nitrogen, sulfur, phosphorus, potassium, zinc, and copper, whereas factor 2 was weighted heavily on the quantities of zinc, iron, and aluminum. Factor 1 varied by oak species, with Q. kelloggii having a higher factor 1 nutrient content than the other three species. Factor 2 response was higher in Q. kelloggii, Q. agrifolia, and Q. engelmannii than in Q. chrysolepis. The collective effects of four macronutrients (nitrogen, sulfur, phosphorus, and potassium) and two micronutrients (zinc and copper) suggest that these might be the nutrients directing preferential feeding of A. auroguttatus adults on the foliage of Q. kelloggii. Leaf toughness might also play an important role in feeding preference. Female A. auroguttatus did not show an ovipositional preference among the four oak species.     

Adult female hamsters require long and sustained exposures to heterospecific males to avoid interspecific mating

Interspecific mating normally decreases female fitness. In many species, females avoid heterospecific males innately or by imprinting on their parents. Alternatively, adult females could learn to discriminate against heterospecific males after exposure to such males. For example, Syrian hamster (Mesocricetus auratus) females learn to discriminate between conspecific males and Turkish hamster (M. brandti) males during adulthood by exposure to males of both species. Adult females not previously exposed to Turkish hamster males will mate similarly with conspecific and heterospecific males. However, in a previous study we showed that exposure to a heterospecific male and a conspecific male for 8 days led to mating avoidance and aggression towards the heterospecific male. Here we conducted two experiments to investigate how much exposure to the heterospecific male was required for females to avoid mating with the heterospecific male (Experiment 1) and how long that avoidance lasted in the absence of continuous exposure to heterospecific stimuli (Experiment 2). Fast and durable learning would indicate the evolution of an efficient avoidance response. In Experiment 1, females were exposed to a heterospecific male for 1, 4 h, 4 or 8 days and then paired with that male. We found more avoidance of interspecific mating after 4 or 8 days of exposure than after 1 or 4 h of exposure. In Experiment 2, females were exposed to a heterospecific male for 8 days and then paired with that male either 10 min later or 8 days later. We found that after an 8-day delay females were highly sexually receptive to the heterospecific male. Additionally, a comparison between the current experiments and a previous study indicates that female Syrian hamsters do not require concurrent exposure to a conspecific male and a heterospecific male to learn to avoid interspecific mating; exposure to a heterospecific male is sufficient.     

Turbidity alters pre‐mating social interactions between native and invasive stream fishes

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Interspecific interactions and learning variability jointly drive geographic differences in mate preferences

Co‐occurrence of closely related species can cause behavioral interference in mating and increase hybridization risk. Theoretically, this could lead to the evolution of more species‐specific mate preferences and sexual signaling traits. Alternatively, females can learn to reject heterospecific males, to avoid male sexual interference from closely related species. Such learned mate discrimination could also affect conspecific mate preferences if females generalize from between species differences to prefer more species‐specific mating signals. Female damselflies of the banded demoiselle (Calopteryx splendens) learn to reject heterospecific males of the beautiful demoiselle (C. virgo) through direct premating interactions. These two species co‐occur in a geographic mosaic of sympatric and microallopatric populations. Whereas C. virgo males have fully melanized wings, male C. splendens wings are partly melanized. We show that C. splendens females in sympatry with C. virgo prefer smaller male wing patches in conspecific males after learning to reject heterospecific males. In contrast, allopatric C. splendens females with experimentally induced experience with C. virgo males did not discriminate against larger male wing patches. Wing patch size might indicate conspecific male quality in allopatry. Co‐occurrence with C. virgo therefore causes females to prefer conspecific male traits that are more species specific, contributing to population divergence and geographic variation in female mate preferences.