Limited dispersal and its effect on population structure in the milkweed beetle Tetraopes tetraophthalmus

Summary The movement patterns of adult milkweed beetles, Tetraopes tetraphthalmus, were monitored via a mark-recapture technique. Movement or dispersal patterns were studied in two natural populations, one in which the host plant, Asclepias syriaca, was nearly continuously distributed over a 250×90 m area and another where Asclepias was distributed in 17 small discrete patches. In both populations dispersal distances resulting from the flight patterns of the adult beetles were quite short, averaging less than 40 m from the point of first encounter 10 days after marking. Males were shown to be more vagile than females. The distribution of dispersal distances collected from one of the populations was fit to three statistical distributions cited in the literature as expected from dispersal by many small-scale movements or observed in other species. It was found that an equation describing an exponential decay gave the best statistical fit to the data collected here for milkweed beetles. The data is discussed in the context of the effects of the limited dispersal power of the beetles and the distribution of suitable habitat on the population structure of Tetraopes.     

Interpatch movement of the red milkweed beetle,Tetraopes tetraophthalmus: individual responses to patch size and isolation

Individual movement patterns and the effects of host plant patch size and isolation on patch occupancy were examined for red milkweed beetles, Tetraopes tetraophthalmus, residing in a heterogeneous landscape. Male beetles were found to move both more often and farther between host plant patches than female beetles, and this difference affected the patterns of patch occupancy observed. Overall, unoccupied milkweed patches were smaller and more isolated than patches occupied by beetles. Patches uninhabited by females tended to be more isolated, but not necessarily smaller, than patches with female beetles, indicating that females may be affected more by patch isolation than patch size. Presence of male beetles on patches showed a stronger response to patch size than to patch isolation. Differences in movement between males and females illustrate the need for demographically based dispersal data. Comparisons of Tetraopes interpatch movement patterns between landscapes composed of patches of different size revealed that landscapes with overall smaller patches may have greater rates of interpatch movement.     

Evolution of climatic niche specialization: a phylogenetic analysis in amphibians

The evolution of climatic niche specialization has important implications for many topics in ecology, evolution and conservation. The climatic niche reflects the set of temperature and precipitation conditions where a species can occur. Thus, specialization to a limited set of climatic conditions can be important for understanding patterns of biogeography, species richness, community structure, allopatric speciation, spread of invasive species and responses to climate change. Nevertheless, the factors that determine climatic niche width (level of specialization) remain poorly explored. Here, we test whether species that occur in more extreme climates are more highly specialized for those conditions, and whether there are trade-offs between niche widths on different climatic niche axes (e.g. do species that tolerate a broad range of temperatures tolerate only a limited range of precipitation regimes?). We test these hypotheses in amphibians, using phylogenetic comparative methods and global-scale datasets, including 2712 species with both climatic and phylogenetic data. Our results do not support either hypothesis. Rather than finding narrower niches in more extreme environments, niches tend to be narrower on one end of a climatic gradient but wider on the other. We also find that temperature and precipitation niche breadths are positively related, rather than showing trade-offs. Finally, our results suggest that most amphibian species occur in relatively warm and dry environments and have relatively narrow climatic niche widths on both of these axes. Thus, they may be especially imperilled by anthropogenic climate change.     

Evolution of host specialization in the Adelgidae (Insecta: Hemiptera) inferred from molecular phylogenetics

The Adelgidae form a small group of insects in the Aphidoidea. They are cyclically parthenogenetic with host alternating, multiple-generation complex life cycles and are restricted to certain host genera in the Pinaceae. Species that host alternate always have Picea as the primary host where sexual reproduction and gall formation occur, and another genus in the Pinaceae as the secondary host where a series of parthenogenetic generations are produced. Other species that do not host alternate complete their entire life cycle on one host and only reproduce parthenogenetically. We studied relationships within Adelgidae using DNA sequences from the mitochondrial COI, COII, and cytb genes, and the nuclear EF1alpha gene. Analysis of the combined data resulted in a well-resolved phylogeny in which the major adelgid clades correspond neatly to their association with secondary host genera. Specialization on each secondary host genus occurred only once and was followed by diversification on the host genus. Molecular dating of divergence times in the Adelgidae suggest that diversification among host genera occurred in the Late Cretaceous and Early Tertiary when the Pinaceae genera were diverging. It is not clear, however, whether the Adelgidae and Pinaceae co-diversified because the relationships among the Pinaceae genera are not fully resolved. We discuss implications for adelgid taxonomy, life cycle evolution, and evolution of the interaction between adelgids and their host plants.     

Evolution of feeding specialization in Tanganyikan scale-eating cichlids: a molecular phylogenetic approach

Background  

Cichlid fishes in Lake Tanganyika exhibit remarkable diversity in their feeding habits. Among them, seven species in the genus Perissodus are known for their unique feeding habit of scale eating with specialized feeding morphology and behaviour. Although the origin of the scale-eating habit has long been questioned, its evolutionary process is still unknown. In the present study, we conducted interspecific phylogenetic analyses for all nine known species in the tribe Perissodini (seven Perissodus and two Haplotaxodon species) using amplified fragment length polymorphism (AFLP) analyses of the nuclear DNA. On the basis of the resultant phylogenetic frameworks, the evolution of their feeding habits was traced using data from analyses of stomach contents, habitat depths, and observations of oral jaw tooth morphology.     

Evolutionary assembly of the milkweed fauna: cytochrome oxidase I and the age of Tetraopes beetles

The insects that feed on the related plant families Apocynaceae and Asclepiadaceae (here collectively termed "milkweeds") comprise a "component community" of highly specialized, distinctive lineages of species that frequently sequester toxic cardiac glycosides from their host plants for defense against predators and are thus often aposematic, advertising their consequent unpalatability. Such sets of specialized lineages provide opportunities for comparative studies of the rate of adaptation, diversification, and habitat-related effects on molecular evolution. The cerambycid genus Tetraopes is the most diverse of the new world milkweed herbivores and the species are generally host specific, being restricted to single, different species of Asclepias, more often so than most other milkweed insects. Previous work revealed correspondence between the phylogeny of these beetles and that of their hosts. The present study provides analyses of near-complete DNA sequences for Tetraopes and relatives that are used to establish a molecular clock and temporal framework for Tetraopes evolution with their milkweed hosts.     

Some consequences for a parasitic herbivore,the milkweed longhorn beetle,Tetraopes tetrophthalmus,of a host-plant shift from Asdepias syriaca to A. verticillata

Summary The impact of differences in host plants on individuals and populations of insect herbivores was investigated using the milkweed longhorn beetle, Tetraopes tetrophthalmus (Forster), larvae of which feed parasitically on host rhizomes. One host, Asclepias syriaca L., was larger in stem and rhizome diameter and grew in cooler soil than the other host, A. verticillata L. The major effects on beetles were retarded phenology at the cooler site and reduced size on the smaller host. Reduced size of beetles was correlated with several important individual attributes: reduced length of life, number of ovarioles, egg size, and a reduced probability of mating with large beetles. The population consequences of these characteristics, largely inferred from these observations, were little or no outbreeding in the small population on A. verticillata.     

Evolution of host acceptance and its reversibility in a seed beetle

1. Adapting to a low‐quality plant may require modification of an insect's digestive physiology, oviposition behaviour, or other host‐use traits. If colonising a marginal host entails a cost, a decay in adaptation would be expected after selection is relaxed, i.e. if populations on a novel host are reverted to their high‐quality ancestral host. 2. Replicate lines of the seed beetle Callosobruchus maculatus (F.) rapidly adapted to lentil seeds; larval survival rose from approximately 1 to ≥ 90%, and oviposition on lentil increased more than two‐fold. This study compared egg‐laying behaviour in lines that either remained on lentil or were reverted to the ancestral host, mung bean, for 22–62 generations. 3. Consistent with the trade‐off hypothesis, females from two reverted sublines showed decreased oviposition on lentil (estimated as lifetime fecundity), but host acceptance in a third subline was unchanged. In a short‐term assay, acceptance of lentil by newly emerged females was lower in each reverted subline than in the corresponding non‐reverted one. Because effective population sizes (determined from genome resequencing) were large throughout the experiment, this decline in host acceptance is unlikely to be explained solely by genetic drift. 4. Variation among replicates in the magnitude of the reversion effect was also observed in a previous study of larval survival. However, the pattern of variation for survival was not congruent with the pattern of variation for host acceptance in this study. Thus, genes mediating improved performance on lentil appear to be largely independent of those responsible for increased oviposition.     

Evolutionary variations on a theme: host plant specialization in five geographical populations of the leaf beetle Chrysomela lapponica

The ancestral host plants of Chrysomela lapponica are Salicaceae rich in salicylic glycosides (SGs), which serve as precursors for larval chemical defensive secretions. Nevertheless, some populations have shifted to plants poor in SGs or even lacking these compounds. To study whether this shift is accompanied by adaptations to novel SG-poor host plants, we reared C. lapponica larvae from five geographical populations on host plants with high (Salix myrsinifolia) or low (S. caprea) SG content. Individuals from two populations (Finland and Kola region in Russia) associated in nature with SG-rich S. myrsinifolia showed higher survival and shorter developmental time on native host species than on foreign SG-poor S. caprea, thus demonstrating local adaptations to their ancestral SG-rich host plant. Individuals from a Belarus population associated in nature with SG-poor S. caprea showed higher survival on this species than on foreign SG-rich S. myrsinifolia, thus demonstrating local adaptation to the novel SG-poor host. On the other hand, individuals from two other populations associated in nature with SG-poor plants (Baikal and Ural region) performed equally well on both SG-rich S. myrsinifolia and SG-poor S. caprea in our rearing experiments, thus showing no local adaptation to a specific SG-host type, but rather a wide feeding niche including several Salicaceae species of different SG-type. Our results suggest that diet breadth of C. lapponica is a local phenomenon, and that adaptation strategies to novel host plants may differ between populations of a single leaf beetle species.     

Geographic variation of host use in the leaf beetle Agelasa nigriceps suggests host range expansion

Host range expansion is an important event in the evolution of host use in phytophagous insects. Herein, we report geographic variation of host use in the chrysomelid leaf beetle, Agelasa nigriceps Motschulsky (Coleoptera: Chrysomelidae), and suggest that this beetle is expanding its host range. This beetle has been recently recorded on Pterostyrax hispidus Sieb. et Zucc. (Styracaceae) in addition to its common host plant Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq. (Actinidiaceae). The A. arguta‐associated populations were widely found in Japan, whereas the P. hispidus‐associated populations were found only in central and southwestern Japan. In the present study, we examined adult feeding behavior and larval performance of 12 A. nigriceps populations collected from eight localities, four localities where beetles occurred only on A. arguta (allopatric localities) and four localities where A. arguta‐ and P. hispidus‐associated populations occurred sympatrically (sympatric localities). Beetles of all populations, irrespective of their host plants and localities, showed high acceptance of and high larval performance on A. arguta leaves. In contrast, we found considerable variation in the beetle response to P. hispidus leaves. The A. arguta‐associated populations of allopatric localities scarcely accepted P. hispidus leaves, whereas those of sympatric localities, particularly those of P. hispidus‐associated populations, accepted and grew on P. hispidus leaves, although the degree of acceptance and larval performance varied among localities. These results strongly suggest that A. arguta is the ancestral host for A. nigriceps, and host range expansion to the P. hispidus has occurred in this beetle.     

Molecular phylogenetic assessment of host range in five Dermanyssus species

Given that 14 out of the 25 currently described species of Dermanyssus Dugès, 1834, are morphologically very close to each another, misidentifications may occur and are suspected in at least some records. One of these 14 species is the red fowl mite, D. gallinae (De Geer, 1778), a blood parasite of wild birds, but also a pest in the poultry industry. Using molecular phylogenetic tools we aimed to answer two questions concerning host specificity and synanthropicity: (1) is D. gallinae the only species infesting European layer farms?, and (2) can populations of D. gallinae move from wild to domestic birds and vice versa? Mitochondrial cytochrome oxidase I gene sequences were obtained from 73 Dermanyssus populations collected from nests of wild European birds and from poultry farms and these were analyzed using maximum parsimony and Bayesian inference. Mapping of the observed host range on the obtained topology and correlation with behavioural observations revealed that (1) host range is strongly dependent on some ecological parameters (e.g. nest hygiene, exposure to pesticides and predators), that (2) out of five species under test, synanthropic populations were found only in lineages of D. gallinae, and that (3) at least some haplotypes found in wild birds were very close to those found in association with domestic birds.     

Evolution of feeding preference in a leaf beetle: the importance of phenotypic plasticity of a host plant

Much attention has been paid to ecology and evolution of damage-induced plant responses. Recently, it has been emphasized that phenotypic plasticity, such as induced plant responses, has the potential to lead to evolutionary changes of interacting partners. Here, we report that induced plant regrowth promotes a locally adaptive feeding preference of a leaf beetle, Plagiodera versicolora . We found that there was among-population variation in the strength of the feeding preference of the leaf beetle for leaf-age types of conspecific host plants. The strength of the preference was positively correlated to leaf production of host plants across populations, and the intensity of induced regrowth was likely to have been responsible for geographic variation in new leaf production. Within one population, we detected a significant additive genetic variance and heritability in the preference for consuming new vs. old leaves. Moreover, the strength of preference was significantly related to egg production depending on the leaf-age types. Thus, allopatric populations can evolutionarily develop different adaptive preference, according to locally distinct patterns of induced host regrowth.     

Divergent host plant specialization as the critical driving force in speciation between populations of a phytophagous ladybird beetle

Detecting the isolating barrier that arises earliest in speciation is critically important to understanding the mechanism of species formation. We tested isolating barriers between host races of a phytophagous ladybird beetle, Henosepilachna diekei (Coleoptera: Coccinellidae: Epilachnine), that occur sympatrically on distinct host plants. We conducted field surveys for the distribution of the beetles and host plants, rearing experiments to measure six potential isolating factors (adult host preference, adult and larval host performance, sexual isolation, egg hatchability, F(1) hybrid inviability, and sexual selection against F(1) hybrids), and molecular analyses of mitochondrial ND2 and the nuclear ITS2 sequences. We found significant genetic divergence between the host races, and extremely divergent host preference (i.e. habitat isolation) and host performance (i.e. immigrant inviability), but no other isolating barriers. The fidelity to particular host plants arises first and alone can prevent gene flow between differentiating populations of phytophagous specialists.     

Egg cannibalism by larvae and adults of the milkweed leaf beetle (Labidomera clivicollis, Coleoptera: Chrysomelidae)

Abstract.

• 1 Egg cannibalism is a form of infanticide that has been implicated in the evolution of guarding of eggs and immatures in some species of insects. The milkweed leaf beetle, Labidomera clivicollis (Coleoptera: Chrysomelidae), exhibits three types of egg cannibalism in the field: siblicide, cannibalism of eggs by older larvae from earlier hatching egg clutches, and cannibalism of eggs by adult females. Unlike their close relative, L.suterella (Choe, 1989), female L.clivicollis do not guard their eggs or immatures. They move slowly about a patch of milkweeds laying multiple egg clutches.
• 2 First instar and older larvae cannibalized eggs in two geographically separated study populations (subspecies) in Austin, Texas, and Bridgeport, New York, U.S.A. Although adult females of both populations cannibalized eggs in the laboratory, only the Texas subspecies, L.c.rogersii, exhibited such cannibalism in the field.
• 3 In the field, correlates of siblicide varied both temporally (within subspecies) and spatially (between subspecies) in terms of whether they were statistically significant, but trends were all in the same direction. Group size was positively correlated with hatching success and siblicide, but negatively correlated with other types of predation. Siblicide was also positively correlated with egg density in a laboratory study of the Texas subspecies, L.c.rogersii.
• 4 In the laboratory, an average of 15–17% of L.c.clivicollis eggs never developed embryos. Although these were almost always cannibalized, some viable eggs were also eaten and there is no evidence that females increased the proportion of infertile eggs they laid to increase siblicide.
• 5 Field data and laboratory experiments showed that adult female L. c.rogersii cannibalized eggs while males rarely did. Females preferentially ate the eggs of other females over their own eggs in an experiment that removed spatial cues.
• 6 Although the selective context of cannibalism is not demonstrated here, I suggest that females may increase siblicide by increasing egg density and may cannibalize eggs to protect their own eggs from being eaten by second and third instar larvae produced by other females.

     

Praon Haliday (Hymenoptera: Braconidae: Aphidiinae) of Southeastern Europe: key, host range and phylogenetic relationships

A review of species in the genus Praon Haliday, 1833 is presented. Twenty described species are keyed and illustrated with scanning electron micrographs and line drawings. The Praon species presented in this work have been identified from 67 aphid taxa occurring on 120 plant taxa. Furthermore, 87 original parasitoid–aphid–plant associations of the species mentioned in the key are presented. Phylogenetic relationships among Praon species are reconstructed using parsimony and cladistic distance methods. Praon abjectum is the sister taxon to the remaining Praon species. We recognized three species group: “Parapraon”, “dorsale-yomenae” and “rosaecola”. Monophyly is suggested for “Parapraon” species group and paraphyly for “dorsale-yomenae” group. Finally, by phylogenetic reconstruction, a close phylogenetic relationship between “Parapraon” and “dorsale-yomenae” species group was found.     

外来入侵害虫红脂大小蠹对寄主挥发物的反应

2002年,利用寄主挥发性物质(+)-α-蒎烯、(-)-β-蒎烯、3-蒈烯和(-)柠檬烯按不同配比制成诱芯,采用自行研制的挥发物释放装置,在山西省关帝山森林经营局西葫芦林场对危害油松Pinus tabulaeformis Carr.的重大外来入侵林业害虫红脂大小蠹Dendroctomus valens LeConte进行了引诱试验。结果表明,3蒈烯对红脂大小蠹的引诱作用最强,明显优于单独使用(+)-α-蒎烯和(-)-β-蒎烯的诱虫效果,也比北美应用的标准诱芯［(+)- α蒎烯(-)-β-蒎烯与3-蒈烯的比例为1∶1∶1］效果好;在标准诱芯中加入油松另一主要成分-(-)柠檬烯会明显降低诱虫效果。红脂大小蠹引诱剂最佳释放量为150 mg/d。该研究不仅对我国红脂大小蠹的监控具有实际应用意义,也从理论上探讨了红脂大小蠹与寄主油松协同进化的化学生态学过程。     

The role of beetle and host volatiles in host colonization in the European oak bark beetle, Scolytus intricatus (Ratzeburg) (Col., Scolytidae)

Abstract:  To understand the role of chemical signals involved in Scolytus intricatus (Ratzeburg) (Col., Scolytidae) host colonization, the attractiveness of intact and beetle colonized host material was investigated in the field and in the laboratory. In the field, chemical signals operating at long range were investigated by means of sticky traps. In the laboratory, close-range chemical interactions were investigated with an arena olfactometer. Field experiments showed no differences in the attractiveness between infested and non-infested host material. On the contrary, laboratory experiments revealed higher attractiveness of infested host and beetle-produced frass in comparison with intact host and mechanically produced sawdust respectively. Laboratory data also disclosed the attractiveness of beetle extracts of both sexes. Our data show that: (1) host kairomones play an important role during host colonization, and that (2) S. intricatus does not use a sex-specific secondary attractant system. Differences between results of field and laboratory trials are discussed.     

Divergent host acceptance behavior suggests host specialization in populations of the polyphagous mite Abacarus hystrix (Acari: Prostigmata: Eriophyidae)

For phytophagous arthropods, host acceptance behavior is a key character responsible for host plant specialization. The grain rust mite, Abacarus hystrix (Nalepa), is an obligately phytophagous, polyphagous eriophyid mite recorded from at least 70 grass species. In this study, the hypothesis that two host populations of this mite (one collected from quackgrass and the other from ryegrass) are highly host-specific was tested using behavioral data. For this purpose, female behavior when exposed to familiar and novel host plants was observed in no-choice cross experiments. Altogether, 13 variables were used to describe mite behavior. Data were subjected to principal component analysis, and host acceptance behavior was subsequently tested with generalized estimating equations (GEE). Distinct variation in female behavior between familiar and novel hosts was observed. Females from neither population accepted novel hosts. This was recorded as significant differences in the occupation of and overall activity on particular plant parts. On their familiar host, females were not active and showed little tendency to move. On novel hosts females were more active and mobile, spending more time walking, running, and climbing on the whole plant surface and showing a tendency to disperse. Other differences in behavior between studied populations were also observed. Thus, the results suggest that mites of these two studied populations (1) differ in their behaviors during plant exploitation and (2) can quickly distinguish between their familiar host and an unfamiliar host used by a conspecific. These findings support the hypothesis of narrow host specialization of ryegrass and quackgrass populations of this highly polyphagous species.     

Thermal death kinetics of red flour beetle (Coleoptera: Tenebrionidae)

While developing radio frequency heat treatments for dried fruits and nuts, we used a heating block system developed by Washington State University to identify the most heat-tolerant life stage of red flour beetle, Tribolium castaneum (Herbst), and to determine its thermal death kinetics. Using a heating rate of 15 degrees C/min to approximate the rapid heating of radio frequency treatments, the relative heat tolerance of red flour beetle stages was found to be older larvae > pupae and adults > eggs and younger larvae. Lethal exposure times for temperatures of 48, 50, and 52 degrees C for the most heat-tolerant larval stage were estimated using a 0.5th order kinetic model. Exposures needed for 95% mortality at 48 degrees C were too long to be practical (67 min), but increasing treatment temperatures to 50 and 52 degrees C resulted in more useful exposure times of 8 and 1.3 min, respectively. Red flour beetle was more sensitive to changes in treatment temperature than previously studied moth species, resulting in red flour beetle being the most heat-tolerant species at 48 degrees C, but navel orangeworm, Amyelois transitella (Walker), being most heat tolerant at 50 and 52 degrees C. Consequently, efficacious treatments for navel orangeworm at 50-52 degrees C also would control red flour beetle.     

The host range ofTetranychus lintearius (Acarina: Tetranychidae)

The host range ofTetranychus lintearius was examined experimentally to determine if the mite could be safely introduced into New Zealand for the biological control of gorse,Ulex europaeus (Leguminosae: Genisteae). The rationale for choosing test plants was the same as that employed for testing insect species as biological control agents. Outdoors, mite colonies could be transferred successfully from gorse plant to gorse plant, but could not re-establish on any of 39 other plant species progeny to develop, was measured on 58 plant species other than gorse. Apart fromUlex europaeus andU. minor, development was completed only onPhaseolus vulgaris andGlycine max. Further experiments using 22 bean cultivars showed that mites could not complete a second generation on detached leaf cultures, could not form permanent colonies on potted plants in the glasshouse, and remanned only a short time when transferred to bean plants in the field. Tetranychus lintearius has never been recorded from any plant butUlex species. This fact, coupled with the results of host-range testing, suggests that the mite is sufficiently host-specific to be safely used as a biological control agent for gorse in New Zealand.