Contemporary evolution of host plant range expansion in an introduced herbivorous beetle Ophraella communa

Host range expansion of herbivorous insects is a key event in ecological speciation and insect pest management. However, the mechanistic processes are relatively unknown because it is difficult to observe the ongoing host range expansion in natural population. In this study, we focused on the ongoing host range expansion in introduced populations of the ragweed leaf beetle, Ophraella communa, to estimate the evolutionary process of host plant range expansion of a herbivorous insect. In the native range of North America, O. communa does not utilize Ambrosia trifida, as a host plant, but this plant is extensively utilized in the beetle's introduced range. Larval performance and adult preference experiments demonstrated that native O. communa beetles show better survival on host plant individuals from introduced plant populations than those from native plant populations and they also oviposit on the introduced plant, but not on the native plant. Introduced O. communa beetles showed significantly higher performance on and preference for both introduced and native A. trifida plants, when compared with native O. communa. These results indicate the contemporary evolution of host plant range expansion of introduced O. communa and suggest that the evolutionary change of both the host plant and the herbivorous insect involved in the host range expansion.     

Effects of high temperature on body size and weight of Ophraella communa

Ophraella communa LeSage (Coleoptera: Chrysomelidae) is an effective biological control agent of the invasive common ragweed, Ambrosia artemisiifolia L. Body size, one of the most important life-history characters for many insects, affects O. communa mating choice. Temperature is one of the most important factors on body size, especially high temperatures. Adult body lengths were significantly inhibited after eggs, larvae and pupae of O. communa experienced high temperature stresses. With exception of subsequent female body after exposure of larvae to high temperatures, the body weights of females and males were not affected by temperatures. Since adult insect fecundities are often in proportion to their body sizes, we concluded that high temperatures may influence the population expansion of O. communa in the field.     

Population abundance and host use pattern of Ophraella communa (Coleoptera: Chrysomelidae) in its native and introduced range

We found that the abundance of Ophraella communa, a specialist herbivore of the invasive weeds Ambrosia artemisiifolia and A. trifida, is higher in the introduced range than in its native range. We also found that the native O. communa does not feed on A. trifida, but introduced O. communa does so extensively.     

Reevaluation of biosecurity of Ophraella communa against sunflower (Helianthus annuus)

Ophraella communa (Coleoptera: Chrysomelidae), originally from North America, has been used for biological control of common ragweed, Ambrosia artemisiifolia, in China since 2007. However, there is still a debate on whether O. communa can attack sunflowers under field conditions. To re-evaluate the biosecurity of O. communa against sunflower (Helianthus annuus), we investigated the population density of O. communa on three sunflower varieties that were intercropped with or planted in circumambience of A. artemisiifolia under field conditions. Our results showed that only very few O. communa eggs (<0.5 eggs/plant) were found on sunflower plants at the last two surveys when sunflowers were planted in circumambience of common ragweed. O. communa eggs were not found on sunflower plants at each survey when sunflowers were intercropped with common ragweed. The first–second instar larvae, third instar larvae, pupae and adults of O. communa were occasionally found on sunflower plants, but their densities were very low under either case of planting patterns. Based on these results, we conclude that sunflower is not a potential host plant for O. communa and the beetle is an effective host-specific biological control agent of common ragweed.     

Lineage divergence and speciation in the Web‐toed Salamanders (Plethodontidae: Hydromantes) of the Sierra Nevada,California

Peripatric speciation and the importance of founder effects have long been controversial, and multilocus sequence data and coalescent methods now allow hypotheses of peripatric speciation to be tested in a rigorous manner. Using a multilocus phylogeographical data set for two species of salamanders (genus Hydromantes) from the Sierra Nevada of California, hypotheses of recent divergence by peripatric speciation and older, allopatric divergence were tested. Phylogeographical analysis revealed two divergent lineages within Hydromantes platycephalus, which were estimated to have diverged in the Pliocene. By contrast, a low‐elevation species, Hydromantes brunus, diverged from within the northern lineage of H. platycephalus much more recently (mid‐Pleistocene), during a time of major climatic change in the Sierra Nevada. Multilocus species tree estimation and coalescent estimates of divergence time, migration rate, and growth rate reject a scenario of ancient speciation of H. brunus with subsequent gene flow and introgression from H. platycephalus, instead supporting a more recent divergence with population expansion. Although the small, peripheral distribution of H. brunus suggests the possibility of peripatric speciation, the estimated founding population size of the species was too large to have allowed founder effects to be important in its divergence. These results provide evidence for both recent speciation, most likely tied to the climatic changes of the Pleistocene, and older lineage divergence, possibly due to geological events, and add to evidence that Pleistocene glacial cycles were an important driver of diversification in the Sierra Nevada.     

Review of the biology and ecology of a ragweed leaf beetle,Ophraella communa (Coleoptera: Chrysomelidae), which is a biological control agent of an invasive common ragweed,Ambrosia artemisiifolia (Asterales: Asteraceae)

A ragweed leaf beetle, Ophraella communa (Coleoptera: Chrysomelidae), has been highlighted as a potential biological control agent of Ambrosia artemisiifolia. O. communa and A. artemisiifolia are native in North America and alien species in East Asia and Europe. As an invasive weed, A. artemisiifolia causes severe economic losses as reducing agricultural production as well as producing severe allergenic pollen. As an herbivore insect, O. communa has strong host preference on A. artemisiifolia. All the developmental stages of O. communa can be found on A. artemisiifolia and it attacks a single plant in repeated and extended manners. With few individuals on A. artemisiifolia, O. communa can completely defoliate before pollen production. Therefore, O. communa had been focused as a biological control of this invasive weed, but its introduction was denied because of possible damage on an important crop, Helianthus annuus. O. communa was accidentally introduced in East Asia and Europe in 1990s and 2010s, respectively. Fortunately, O. communa population was well established to suppress A. artemisiifolia in the introduced areas. Following detailed field surveys and host specificity tests of O. communa were conducted and proved a strong potential of O. communa as a biological control agent of A. artemisiifolia. Moreover, O. communa has been investigated in physiological and evolutionary studies. In this study, the potential of O. communa as a biological control agent and a study organism are reviewed.     

永州广聚萤叶甲和豚草卷蛾的种群动态及对豚草的控制效果

【目的】豚草是一种重要的入侵杂草,严重危害农业生产和人类健康。广聚萤叶甲和豚草卷蛾是豚草的专一性天敌。研究这2种天敌在永州的种群动态及其对豚草的控制效果,可以为永州豚草的防控及这2种天敌的有效利用提供依据。【方法】在湖南省永州市江永县豚草大面积发生区域,人工释放广聚萤叶甲和豚草卷蛾,调查这2种天敌在释放区和扩散区的种群动态和对豚草的防治效果,以及这2种天敌在扩散区的越冬情况。【结果】广聚萤叶甲和豚草卷蛾的扩散能力强。释放1个月后,在释放区,广聚萤叶甲各虫态及豚草卷蛾虫瘿均被发现。整体上,随时间延长,广聚萤叶甲各虫态虫口密度先增后减,而豚草卷蛾虫瘿密度呈逐渐降低趋势。释放2个月后,在距释放区边缘10 km的豚草发生区,发现了广聚萤叶甲和豚草卷蛾,且成功建立了种群并顺利越冬。释放区豚草株高几乎没有增加,且叶片最终被取食精光,几乎全部死亡;扩散区豚草株高略有增加,最终近75%叶片被取食。【结论】广聚萤叶甲和豚草卷蛾可在永州成功建立种群并安全越冬,还能自行扩散,可持续控制野外豚草的发生。     

Effect of humidity on the development and fecundity of <Emphasis Type="Italic">Ophraella communa</Emphasis> (Coleoptera: Chrysomelidae)

Ophraella communa, an unintentionally introduced leaf beetle in China, has good control efficiency on ragweed, Ambrosia artemisiifolia. Aspects of the climatic requirements for development, survival, longevity and fecundity of O. communa were studied under the conditions of constant temperature (25 ± 1°C), photoperiod of 14 L:10 D and three relative humidities (60%, 75% and 90% RHs). The results showed that the developmental periods of O. communa at different stages shortened along with the increasing relative humidity, except that of the pupal stage. Although no differences were observed in the pupal survival rate, ovipositional period, fecundity, longevity and adult female age-specific survivorship of O. communa under the three humidity conditions, the survival rates during the egg, larva and entire immature stage were significantly higher at 75% RH and 90% RH than at 60% RH. The innate rate of increase (r _m), net reproductive rate (R ₀), finite rate of increase (λ) reached the maximum at 75% RH, with values of 0.181, 1116.4 and 1.198, respectively. These results indicated that the optimum relative humidity for the development of O. communa ranged from 75% RH to 90% RH. Thus O. communa prefers moist microclimate habitats. Its population may expand rapidly during mid-May to late August in south, east and central China, when the humidity is relatively high.     

Food deprivation-dependent development and fecundity in Ophraella communa

Ophraella communa LeSage is native to North America and a biological control agent of the invasive weed Ambrosia artemisiifolia L. Since A. artemisiifolia plants grow old and die after September annually, O. communa suffers from food shortage. To understand the effect of food shortage or deprivation on population fitness of O. communa, the development and fecundity and hatchability of its progeny eggs were observed when larvae were offered A. artemisiifolia plants for either 3, 6, 12 or 24 hours daily. The results showed that larval food deprivation significantly influenced survival and developmental durations of larvae and pupae. Survival rates and developmental durations of larvae and pupae decreased and were prolonged significantly with decreasing time of larval daily food intake. Longevity and fecundity of adults shortened and decreased significantly with decreasing time of larval daily food intake. In addition, the hatch rates of progeny eggs decreased significantly with decreasing time of larval daily food intake. The present study suggests that food shortage is one of the most critical factors that suppresses O. communa populations. This can explain why field populations of the beetle decrease significantly with ageing and death of A. artemisiifolia plants after late September.     

Rapid evolution of an introduced insect Ophraella communa LeSage in new environments: temporal changes and geographical differences in photoperiodic response

The accidentally introduced beetle Ophraella communa was first found in 1996 in Japan and has rapidly expanded its distribution range to include regions with substantially different climates. During this range expansion and subsequent establishment in new habitats, the life history traits of O. communa have changed depending on new habitat environmental conditions. In this study, we investigated the photoperiodic response of O. communa controlling its reproductive diapause, an important trait that adjusts the life cycle to local climate and phenology of host‐plants. We examined temporal changes and geographical differences in this trait. In the Tsukuba population of O. communa, the diapause incidence under conditions of 12 h light : 12 h dark (LD 12:12), 13:11 and 14:10 did not consistently increase or decrease during 2005–2012, although it fluctuated yearly. The diapause incidence in this period, however, was lower than that in 1999 reported previously and the critical day‐length inducing diapause was shortened by >1 h from 1999 to 2005. These results suggest that the photoperiodic response of O. communa shifted during this period. To examine geographical differences in this trait, we compared the Hirosaki, Morioka, Tsukuba and Koshi lines. The diapause incidence at LD 13:11 was significantly different between the O. communa lines: 86.5% in the Hirosaki line (collected in 2010) , 81.4% in Morioka (collected in 2010), 45.0% in Tsukuba (collected in 2011) and 7.1% in Koshi (collected in 2009), and was positively correlated with the latitude of the origin. These results suggest that this trait shifted, responding to the environmental conditions in the colonized regions.     

Rapid cold-hardening response in Ophraella communa LeSage (Coleoptera: Chrysomelidae), a biological control agent of Ambrosia artemisiifolia L.

In China, an unintentionally introduced beetle Ophraella communa shows good control efficiency against invasive common ragweed, Ambrosia artemisiifolia. With the aim of understanding the capacity of O. communa to overcome sub-zero low temperature rapidly, the longevity, survival and fecundity of the beetle adults were studied at conditions of different rapid cold-hardening in the laboratory. The results showed that approximately 20% female or male individuals still survive at ?12°C for 2 h, thus the discriminating temperature for rapid cold-hardening of both female and male beetles is ?12°C. The survival, longevity and fecundity of adult beetles were significantly affected by rapid cold-hardening treatments. Compared to the control, the survival rates of adult beetles experiencing 2 h of rapid cold-hardening at 2, 5 and 8°C prior to exposure to its discriminating temperature (?12°C) were significantly increased. Adult longevity and fecundity were significantly higher after pre-treatment at 2, 5 and 8°C for 2 h than those of the control. Both longest longevity and maximum fecundity of adult beetles were observed at the rapid cold-hardening of 2°C. Our experiment implies that the cold-tolerance ability of O. communa can be rapidly increased after rapid cold-hardening treatments, which reveals an important ecological significance for population establishment and expansion of O. communa in the invaded areas of common ragweed.     

Risk to nontarget plants from <Emphasis Type="Italic">Ophraella communa</Emphasis> (Coleoptera: Chrysomelidae), a potential biological control agent of alien invasive weed <Emphasis Type="Italic">Ambrosia artemisiifolia</Emphasis> (Asteraceae) in China

Ophraella communa LeSage is an oligophagous insect that shows promise for controlling the alien invasive weed Ambrosia artemisiifolia L. in China. This study was performed to evaluate the risk of O. communa on the basis of host-specificity testing of larval development under no-choice conditions and of oviposition preferences under choice conditions in greenhouses and in the open field. Under no-choice conditions, O. communa larvae experienced much higher mortality rates on the nontarget plants than on the target weed, but a small proportion of larvae completed development on the nontarget plants examined, including Xanthium sibiricum Patrin ex Widder, Helianthus tuberosus L., and H. annuus L. Multiple-choice tests indicated that O. communa showed a strong oviposition preference for the target weed over the nontarget plants and laid few eggs on the economically important Helianthus crops tested. In paired-choice trials, O. communa adults showed an obvious preference for the target weed over X. sibiricum but preferred X. sibiricum to H. annuus. The results suggest that X. sibiricum might be used as a lower-ranked host plant next to the target weed by O. communa, and that Helianthus crops would not be at risk of being used for oviposition in the field.     

Late Pleistocene climate change promoted divergence between Picea asperata and P. crassifolia on the Qinghai–Tibet Plateau through recent bottlenecks

Divergence during the early stage of speciation can be driven by a population bottleneck via reduced gene flow and enhanced lineage sorting. In this study, we aimed to examine whether such bottlenecks occurred during the initial speciation of two closely related spruce species Picea asperata and P. crassifolia occurring on the Qinghai–Tibet Plateau (QTP). We analyzed sequences of three chloroplast, two mitochondrial DNA fragments and a further 13 nuclear loci from 216 individuals of the two species. Both species showed a low level of genetic diversity in contrast to other congeners occurring in the QTP and adjacent regions. The estimated population sizes of P. asperata and P. crassifolia are less than the ancestral population size before splitting. These results together with multiple statistical tests (Tajima's D, Fu and Li's D* and F*) suggest that these two species underwent recent bottlenecks. Based on approximate Bayesian computation (ABC), we also determined that the period of the population shrinkage was consistent with the interspecific divergence during the late Pleistocene. The reduced population sizes and the divergent selection may together have triggered the initial divergence under high gene flow between these two species. Our results therefore highlight the importance of climatic oscillations during the late Pleistocene in promoting speciation through changing demographic sizes of the ancestral species on the QTP and in adjacent regions.     

Pleistocene climatic oscillations and the speciation history of an alpine endemic and a widespread arctic-alpine plant

Even in cases in which geographic isolation appears to have driven the speciation of regional endemics, range shifts during the Pleistocene climatic oscillations may also have influenced their evolutionary history. Elucidating speciation history can provide novel insights into evolutionary dynamics following climatic oscillations. We demonstrated a sister relationship between the Japanese alpine endemic Cardamine nipponica and the currently allopatric, widespread arctic-alpine Cardamine?bellidifolia (Brassicaceae) based on internal transcribed spacer (ITS) sequences and 10 other nuclear genes. Speciation history was inferred using demographic parameters under the isolation with migration model. The estimated demographic parameters showed that the population size of C. nipponica was similar to that of C. bellidifolia and that gene flow occurred exclusively from C. nipponica to C. bellidifolia after speciation. The inferred speciation history, which included gene flow, suggests that geographic barriers between the peripheral C. nipponica and the widespread C. bellidifolia were reduced during the Pleistocene. The asymmetric introgression implies that genetic isolation may have been involved in the speciation of C. nipponica. Our results suggest that even currently allopatric species may not have diverged solely under geographic isolation, and that their evolutionary history may have been influenced by Pleistocene range dynamics.     

Synergistic effects of olfactory and tactile cues in short‐range mate finding of Ophraella communa

Sensory signals between individuals are important in short‐range mate finding. The purpose of our experiments was to verify the roles of different sensory cues in mate orientation and discrimination in Ophraella communa LeSage (Coleoptera: Chrysomelidae) adults. Sex discrimination and sensory deprivation tests (i.e., depriving the olfactory and/or visual senses of either or both sexes by coating with paint) were conducted in the laboratory. Male O. communa were able to locate and recognize conspecifics using olfactory cues prior to physical contact, but could not discriminate the opposite sex prior to physical contact. When the olfaction of male O. communa was deprived by painting antennae, males spent significantly longer times seeking mates in the arena. Copulation duration did not differ significantly among treatments. Thus, the mating process of O. communa adults was mediated by contact cues, but not by olfactory cues. The percentages of successful mating, searching duration, and copulation duration were all unaffected by visual deprivation, i.e., when the eyes of either or both sexes were covered by black paint. The function of visual cues was thus negligible in the mate‐finding process of O. communa adults. Overall, these results suggested that orientation and discrimination of the opposite sex by O. communa is dependent on the synergy between olfactory and tactile cues.     

Cyclic habitat displacements during Pleistocene glaciations have induced independent evolution of Tasimia palpata populations (Trichoptera: Tasimiidae) in isolated subtropical rain forest patches

Aim Mechanisms generating biodiversity and endemism are influenced by both historical and ecological patterns, and the relative roles of history vs. ecological interactions are still being debated. The phylogeography of one rain forest‐restricted caddisfly species, Tasimia palpata, thought to have good dispersal abilities, is used to address questions about shifts of highland rain forest habitat during Pleistocene glaciations and about their consequences for haplotype composition and distribution. Location Tasimia palpata occurs in highland subtropical rain forest patches, which are separated from one another by lowland dry bush, in south‐eastern Queensland, Australia. Methods We sequenced 375 base pairs of the mitochondrial cytochrome oxidase I gene from 169 individuals (20 populations) of T. palpata, mainly from three fragmented subtropical rain forest blocks, revealing 46 haplotypes. Analysis of molecular variance (amova ), genetic divergence between populations, nested clade analyses and tests based on coalescent theory were used to analyse phylogeographical relationships among T. palpata populations. Results amova indicates spatial genetic structure between isolated subtropical rain forest patches, with an isolation‐by‐distance effect. Tests based on coalescent theory suggest a repeated process of population reductions and divergence between isolated rain forests during Pleistocene glaciations as a consequence of habitat constrictions followed by population expansions during interglacial periods when subtropical rain forest expanded. In addition, these results suggest that, prior to the Pleistocene, rain forest and T. palpata had more widespread distributions in this region. Main conclusions Historical rain forest expansion and contraction during the Pleistocene resulted in changes in demography and genetic diversity of T. palpata, as well as in an increase in genetic divergence between populations from different patches of subtropical rain forest. Despite the fact that this caddisfly species was isolated in separate highland rain forest patches at various times during the Pleistocene, there is no evidence of allopatric speciation during the Quaternary, which contrasts with other examples of endemism and high diversity in rain forest highlands.     

Phylogeographical analysis of an estuarine fish, Salanx ariakensis (Osmeridae: Salanginae) in the north-western Pacific

This study extended the geographic coverage of a previous study to explore population genetic structure and demographic history in the Ariake icefish Salanx ariakensis from three populations of continental coastlines and one island population in the north-western Pacific based on a partial sequence of the mitochondrial cytochrome b gene. The S. ariakensis showed high genetic diversity and strong genetic structure. Phylogenetic analysis showed a shallow gene tree with no clear phylogeographical structure. Contiguous range expansion and restricted gene flow were inferred to be main population events by nested-clade analysis. Significant genetic differentiations between populations could be attributable to negligible gene flow by coalescent analysis. High nucleotide diversity of each population was due to geographic mixing of heterogenous haplotypes during lowering sea levels of the Pleistocene. These findings indicate that cycles of geographic isolation and secondary contact happened in the Pleistocene glacial–interglacial cycles shaping genetic structure and population demography of S. ariakensis .     

Control efficiency of leaf beetle,Ophraella communa,on the invasive common ragweed,Ambrosia artemisiifolia,at different growing stages

Ophraella communa LeSage (Coleoptera: Chrysomelidae), an effective biological control agent of A. artemisiifolia, was unintentionally introduced into China. To understand the biological control potential of O. communa on A. artemisiifolia, plant height, the number of branches and leaf control index of A. artemisiifolia injured by the beetle were determined. The results showed that plant height and number of branches decreased and leaf control index increased with the increasing initial release density of O. communa adults, when they were released at 90–100-cm plant height stage in 2008 and 60–70-cm stage in 2009. Even when O. communa was released at a low average density of 1.07 adults per plant at early growth stage of A. artemisiifolia in 2009, it could significantly suppress plant height and number of branches and led to a higher leaf control index compared with the herbicide treatment with Roundup. Prior to the fructicative period, the leaf control index of A. artemisiifolia by O. communa was up to 1.0 on the 47th day after the average initial release of 12 beetles per plant in 2008 or on the 85th day after the average release of 1.07 beetles per plant in 2009, which was significantly higher than that in the herbicide treatment. We suggest that the initial release average density of O. communa adults should be ≥1.07 beetles per plant at the early growth stage, or ≥12 beetles per plant at the late growth stage for an effective control of A. artemisiifolia in the field.     

Defoliation of common ragweed by Ophraella communa beetle does not affect pollen allergenicity in controlled conditions

Ragweed allergy is one of the primary causes of seasonal allergies in Europe and its prevalence is expected to rise. The leaf beetle Ophraella communa, recently and accidentally established in N-Italy and S-Switzerland, represents a promising approach to control ragweed, but negative side effects should be excluded before its use. Since biotic and abiotic stresses are known to influence the allergenicity of pollen, we set out to assess the effect of sub-lethal defoliation by O. communa on the quantity and quality of ragweed pollen. Seventeen sister pairs (including six clones) of ragweed plants were grown in controlled conditions. One of each pair was exposed to O. communa as soon as the plant started to produce reproductive structures. After 10 weeks of exposure, plant traits were measured as a proxy for pollen quantity. Pollen quality was assessed by measuring its viability and allergenicity. Generally, plants produced very few male flowers and little amount of pollen. Damage by the beetle was severe with most of the leaf tissue removed, but no treatment effect was found on any of the quantitative and qualitative traits assessed. In conclusion, O. communa did not increase the amount or allergenicity of ragweed pollen grains in our experimental conditions.