Cytological evidence supports the taxonomic status of the Sino‐Himalayan species Cimicifuga frigida (Ranunculaceae)

Although Cimicifuga foetida L. (Ranunculaceae) has been shown to be a distinct species distributed only in northern Asia (Siberia, Mongolia), the Sino‐Himalayan species C. frigida Royle remains to be much confused with the Chinese endemic C. mairei H. Lév. The independent species status of C. frigida is recognized by some authors, but refuted by others. A cytogeographical study has shown that the ploidy level is well correlated with the geographical distribution of C. frigida and C. mairei. Cimicifuga frigida is a tetraploid (2n = 32) occurring in the Sino‐Himalayan region, whereas C. mairei is a diploid (2n = 16) occurring in central and southwestern China. There is only minor overlap in their geographical distributions in northwestern Yunnan, China. The ploidy level is also well correlated with the morphological characters, in particular the shape of the staminodes, which has previously been used as the only reliable morphological character to distinguish between C. frigida and C. mairei. The cytogeographical pattern, therefore, lends strong support for the recognition of the independent species status of C. frigida. This species is the only polyploid species currently known in the genus.     

Investigating dietary preferences in two competing dipterans, Coelopa frigida and Coelopa pilipes, using stable isotope ratios of carbon and nitrogen

Two species of seaweed fly, Coelopa frigida (Fabricius) and Coelopa pilipes (Halliday) (both Diptera: Coelopidae: Coelopini), compete for resources within deposits of marine algae washed ashore on British beaches. Previous studies report that adult flies exhibit algal‐specific behaviour that may influence interspecific interactions. It is predicted that coelopid larvae may also demonstrate algal‐specific dietary preferences. Larval dietary preferences are investigated by comparing the ratios of ¹³C/¹²C and ¹⁵N/¹⁴N in both wild flies and macroalgae to those of laboratory‐reared flies. Results showed only a small difference between the stable isotope ratios of the most abundant algae, Laminaria spp. (Laminariaceae) and Fucus spp. (Fucaceae), although there were significant differences between wild adult coelopids. This result illustrates different metabolic processes in two closely related species. The stable isotope ratios of wild‐caught coelopids were found to differ significantly from laboratory‐reared coelopids. This is either the result of red algae in the diet of natural populations or a difference in bacterial communities. We suggest that experiments with laboratory‐reared flies/specimens can greatly increase the utility of stable isotope analysis in the investigation of animal food webs, even where potential diets are isotopically similar. However, this approach is dependent on re‐creations that accurately mimic natural conditions.     

Selection of plant parts by Depressaria multifidae (Lep., Oecophoridae) on its seasonally-restricted hostplant, Lomatium grayi (Umbelliferae)

ABSTRACT.

• 1 Depressaria multifidae Clarke feeds on a broader variety of Umbelliferae plant parts than other Depressaria species.
• 2 Early instar larvae feed in the sheaths surrounding floral buds and leaves. Later instar larvae feed in the sheaths and floral stems and on flowers and leaves.
• 3 Floral stems bored by larvae had significantly larger basal stem diameters than floral stems that were not bored. Smaller stems usually have umbels with only male flowers, and wither after flowering, too soon for larvae to complete development. In contrast, larger stems often have umbels with some hermaphroditic flowers, which remain green and erect long enough for larvae to complete development. Hence, selection may favour larvae that bore only in relatively large stems.
• 4 In the laboratory, larvae fed sheaths with enclosed floral buds, flowers, or leaves all pupated at the same weight, but larvae fed floral stems pupated at a significantly lower weight. Larval and pupal development time was the same on all plant parts.
• 5 In the field, larvae restricted to a single umbel throughout development pupated at the same weight as those restricted to a single leaf.
• 6 Unlike in other Depressaria species, nitrogen levels only partly correspond to the pattern of use of plant parts in D.multifidae. Nitrogen values varied as follows: floral buds > immature leaves ≥ flowers > floral stalks > sheaths excluding floral buds or leaves.
• 7 The broad variety of plant parts used by D.multifidae may result partly from the problem of feeding on a small, seasonally restricted hostplant; the greater use of sheaths and floral stems than in other Depressaria species may result from selection for safety from parasites or predators.
• 8 The results for D.multifidae indicate that the way in which an insect feeds on a plant species can vary broadly even at a single site.

     

Microhabitat selection and life cycle patterns of two Rhyacophila species (Trichoptera: Rhyacophilidae) in southern Ontario streams

SUMMARY.

• 1 Two species of predatory caddisfly larvae—Rhyacophila fuscula (Walker) and R. melita Ross—have overlapping longitudinal distributions in southern Ontario streams.
• 2 The populations were studied at sites in areas of overlap (sympatry) and allopatry to determine what resources were partitioned, and if partitioning varied in the zones of overlap.
• 3 Life cycle and species size variation resulted in substantial physical differences between these univoltine species for most months of the year.
• 4 In May, when larvae of both species were not significantly different in size, a detailed microhabitat field study found no difference in microhabitat use between allopatric populations of R. fuscula and R. melita. Microhabitat selection by R. fuscula remained constant at sympatric sites but R. melita showed a significant change resulting in reduced microhabitat overlap with R. fuscula.

     

Oviposition habitat selection by container‐dwelling mosquitoes: responses to cues of larval and detritus abundances in the field

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Life history features of some macroinvertebrates in a French Polynesian stream

The invertebrate fauna of the Opunohu River catchment in Moorea, French Polynesia, studied 1988–1989, was numerically dominated by four species of neritid snails, one species of thiarid snail, two species of atyid shrimp, two species of palaemonid shrimp, and ten species of coenagrionid, chironomid, and simuliid insect larvae. Numbers of egg capsules of neritid snails were higher in riffles (maximum x density > 10,000/m² surface area) than pools, were highest in riffles in September and pools in August, and were lowest in both habitats in March and December. The snail Neritina canalis Lamarck and the shrimp Atyoida pilipes Newport, Caridina weberi DeMan, Macrobrachium lar Fabricius, and Macrobrachium australe Guerin‐Menévílle are diadromous: they enter freshwater as juveniles and migrate upstream; their larval offspring return to the ocean for growth and development. Ovigerous females of A. pilipes and M. lar were mainly found in austral fall; ovigerous females of C. weberi and M. australe were found in both austral fall and spring. Ovigerous females were the largest individuals of each shrimp species collected. Mean size of N. canalis, A. pilipes, C. weberi, and M. lar was generally larger in upstream than downstream reaches; no such difference was found for the non‐diadromous thiarid snail Melanoides tuberculata Müller. Coenagrionid, chironomid, and simuliid insect larvae have multiple cohort populations but at least one simuliid species occurs as a single cohort. Downstream habitat alteration may strongly influence the distribution of diadromous species.     

Exogenous and endogenous factors acting on the spatial distribution of a chrysomelid in extensively managed blueberry fields

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Variation in the ability of larvae of phytophagous insects to develop on evolutionarily unfamiliar plants: a study with gypsy moth Lymantria dispar and Eucalyptus

• 1 By examining variation in the abilities of polyphagous insects to develop on host plants with secondary metabolites that they have never encountered previously, we may be able to gain some insights into the nature of evolution of biochemical mechanisms to process plant secondary metabolites by phytophagous insects.
• 2 The present study aimed to examine variation in the ability of gypsy moth larvae Lymantria dispar (Lymantriidae) to complete development on different species of the plant genus Eucalyptus (Myrtaceae). Leaves of at least some Eucalyptus species contain formylated phloroglucinol derivatives. These are secondary metabolites that are evolutionarily unfamiliar to the gypsy moth.
• 3 Larvae of gypsy moth showed extremely variable responses in larval performance between Eucalyptus species, between individual trees within host plant species, between moth populations, and between individuals within moth populations.
• 4 Larval survivorship was in the range 0–94%, depending on the host. Failure of at least some larvae to complete development on some Eucalyptus species indicates that gypsy moth larvae have a limited ability to process secondary metabolites in eucalypt leaves.
• 5 At least some individuals, however, appear to already possess biochemical mechanisms that process the secondary metabolites in leaves of Eucalyptus species, and therefore the abilities of larvae to complete development on phylogenetically and chemically unfamiliar hosts are already present before the gypsy moth encounters these potential hosts.

     

Distribution and habitat utilization in two atyid shrimps (Crustacea: Decapoda) in rivers of Nuku-Hiva Island (French Polynesia)

The distribution of Atyoida pilipes (Newport, 1847) and Caridina weberi De Man, 1892 was studied at two spatial scales on Nuku-Hiva Island (Marquesas, French Polynesia). At the stream reach scale, the two species were present at 40 and 39 sites, respectively, out of a total of 49 sites sampled. These two taxa represented more than half of the invertebrates collected at 9 sites. There was no difference in distribution between the species at the reach scale. However, clear differences appeared between the two species at the microhabitat scale. A. pilipes was more abundant in lotic habitats, even waterfalls, while C. weberi was associated with accumulations of leaves in lentic habitats. A. pilipes, particularly males, were tolerant to parameters such as water velocity, leaves, and the presence of algae and rocks. C. weberi had a more restricted altitudinal distribution and were scarce upstream from large waterfalls. These differences were linked to differences in climbing ability rather than the effect of chemical parameters, such as oxygen content. Our results suggest that little competition for space or food resources occurs between the two species. Both are feeding on small detritus particles, but through differing mechanisms and in differing habitats.     

Larval age differences and competition between Drosophila aldrichi and D.buzzatii

Abstract.

• 1 Competitive interactions among larvae of Drosophila species using the same habitat will usually involve individuals varying in age and size. Older, larger larvae might be expected to outcompete younger, smaller larvae.
• 2 Newly hatched laryae of Drosophila aldrichi and D.buzzatii were placed on induced cactus necroses (simulating the natural habitat), either simultaneously, or with a 1 or 2 day difference in the time at which individuals of the other species were added.
• 3 Evidence for competitive differences with larval age were found. In both species, body weight was significantly higher for those larvae added first than for later addition larvae, and a longer time to complete development was required for those larvae added 2 days later. However, pre-adult viability of D.aldrichi was significantly higher for larvae started 1 or 2 days after larvae of D.buzzatii. For D.buzzatii, viability was lowest for larvae started simultaneously with D.aldrichi, but not different between those started either before or after D.aldrichi.
• 4 Considering all three traits, no clear advantage for the early addition larvae was observed.

     

Patterns of resource distribution among conspecific larvae in two fruit fly species: Anastrepha fraterculus and Ceratitis capitata (Diptera: Tephritidae)

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Density-related foraging behaviour in Closterocerus tricinctus, a parasitoid of the leaf-mining moth, Cameraria hamadryadella

• 1 We examined the foraging behaviour of the parasitoid wasp, Closterocerus tricinctus (Ashmead) (Chalcidoidea: Eulophidae), as it visited larvae of the leaf-mining moth, Cameraria hamadryadella (Lepidoptera: Gracillariidae), in an outbreak population.
• 2 We tracked females of C.tricinctus, recording the time spent searching for mines and handling host larvae. The density of leaf-mines (host larvae) and their condition were recorded for each leaf visited. A subset of leaves visited by C.tricinctus was enclosed in fine mesh bags so that foraging success could be determined by rearing or dissection. The average density of mines and the average leaf-area mined was estimated for a random sample of leaves from each tree.
• 3 The selection of leaves upon which to forage appears to be density-dependent. C.tricinctus visits leaves with leaf-mine densities twice the average, and when switching leaves lands directly on leaf-mines 5 times more often than expected assuming random landings.
• 4 The total time spent foraging on a leaf, the average time spent handling hosts, and the total search time within leaves tend to decline on leaves with many hosts, but the observed declines are not statistically significant.
• 5 The proportion of leaf-mines visited within a leaf is strongly inversely density-dependent. 30% of visits to leaf-mines are re-visits and 29% of handling time is spent re-handling previously visited hosts. Furthermore, only 21% of visits to mines lead to successful parasitism. We suggest that self-interference and the avoidance behaviour of the host may reduce the number of visits of leaf-mines by C.tricinctus within a leaf.
• 6 The effect of the strongly inversely density-dependent foraging investment within leaves is to offset the observed density-dependent pattern of leaf visitation making the overall spatial pattern of visitation by C.tricinctus to mines of C.hamadryadella inversely density-dependent.
• 7 We suggest that the uncertainty of C.tricinctus surviving on multiply mined leaves because of density-dependent host mortality due to intraspecific competition in high-density host populations, the rarity of high-density host populations, and the rarity of multiply-mined leaves in low-density host populations combine to select against an aggregative response within leaves by C.tricinctus.

     

Influence of the forest caterpillar hunter Calosoma sycophanta on the transmission of microsporidia in larvae of the gypsy moth Lymantria dispar

• 1 The behaviour of predators can be an important factor in the transmission success of an insect pathogen. We studied how Calosoma sycophanta influences the interaction between its prey [Lymantria dispar (L.) (Lepidoptera, Lymantriidae)] and two microsporidian pathogens [Nosema lymantriae (Microsporidia, Nosematidae) and Vairimorpha disparis (Microsporidia, Burellenidae)] infecting the prey.
• 2 Using laboratory experiments, C. sycophanta was allowed to forage on infected and uninfected L. dispar larvae and to disseminate microsporidian spores when preying or afterwards with faeces.
• 3 The beetle disseminated spores of N. lymantriae and V. disparis when preying upon infected larvae, as well as after feeding on such prey. Between 45% and 69% of test larvae became infected when C. sycophanta was allowed to disseminate spores of either microsporidium.
• 4 Laboratory choice experiments showed that C. sycophanta did not discriminate between Nosema‐infected and uninfected gypsy moth larvae. Calosoma sycophanta preferred Vairimorpha‐infected over uninfected gypsy moth larvae and significantly influenced transmission.
• 5 When C. sycophanta was allowed to forage during the latent period on infected and uninfected larvae reared together on caged, potted oak saplings, the percentage of V. disparis infection among test larvae increased by more than 70%. The transmission of N. lymantriae was not affected significantly in these experiments.
• 6 Beetles never became infected with either microsporidian species after feeding on infected prey.
• 7 We conclude that the transmission of N. lymantriae is not affected. Because no V. disparis spores are released from living larvae, feeding on infected larvae might enhance transmission by reducing the time to death and therefore the latent period.

     

Impacts of biological control and invasive species on a non-target native Hawaiian insect

The potential for classical biological control to cause unintended harm to native species was evaluated in the case of the endemic Hawaiian koa bug, Coleotichus blackburniae White (Hemiptera: Scutelleridae), and parasitoids introduced to Hawaii for control of an agricultural pest, the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae). Parasitism of C. blackburniae eggs, nymphs and adults by biocontrol agents was quantified across a wide range of habitats and compared to other sources of mortality. Egg mortality due to the biocontrol agent Trissolcus basalis Wollaston (Hymenoptera: Scelionidae) was low (maximum 26%) and confined to elevations below 500 m on a single host plant. Predation, mainly by alien spiders and ants, was the greatest source of egg mortality (maximum 87%). Parasitism of adult C. blackburniae by the biocontrol agent Trichopoda pilipes (F.) (Diptera: Tachinidae) was near zero at 21 of 24 sites surveyed. Three sites with high bug density had higher levels of T. pilipes parasitism, reaching maxima of 70% among adult female bugs, 100% among males and 50% among fifth instars. Male-biased parasitism indicated that T. pilipes is adapted to using male aggregation pheromone for finding C. blackburniae hosts. The relative impacts of biocontrol agents and other sources of mortality were compared using life tables. Invasive species, particularly generalist egg predators, had the greatest impacts on C. blackburniae populations. Effects of intentionally introduced parasitoids were relatively minor, although the tachinid T. pilipes showed potential for large impacts at individual sites. In retrospect, non-target attacks by biological control agents on C. blackburniae were predictable, but the environmental range and magnitude of impacts would have been difficult to foresee.     

Larvae of cryptic species of Anopheles gambiae respond differently to cues of predation risk

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Host location by the fruit fly parasitoid Diachasmimorpha krausii: role of fruit fly species,life stage and host plant

• 1 Diachasmimorpha krausii is a braconid parasitoid of larval tephritid fruit flies, which feed cryptically within host fruit. At the ovipositor probing stage, the wasp cannot discriminate between hosts that are physiologically suitable or unsuitable for offspring development and must use other cues to locate suitable hosts.
• 2 To identify the cues used by the parasitoid to find suitable hosts, we offered, to free flying wasps, different combinations of three fruit fly species (Bactrocera tryoni, Bactrocera cacuminata, Bactrocera cucumis), different life stages of those flies (adults and larvae) and different host plants (Solanum lycopersicon, Solanum mauritianum, Cucurbita pepo). In the laboratory, the wasp will readily oviposit into larvae of all three flies but successfully develops only in B. tryoni. Bactrocera tryoni commonly infests S. lycopersicon (tomato), rarely S. mauritianum (wild tobacco) but never C. pepo (zucchini). The latter two plant species are common hosts for B. cacuminata and B. cucumis, respectively.
• 3 The parasitoid showed little or no response to uninfested plants of any of the test species. The presence of adult B. tryoni, however, increased parasitoid residency time on uninfested tomato.
• 4 When the three fruit types were all infested with larvae, parasitoid response was strongest to tomato, regardless of whether the larvae were physiologically suitable or unsuitable for offspring development. By contrast, zucchini was rarely visited by the wasp, even when infested with B. tryoni larvae.
• 5 Wild tobacco was infrequently visited when infested with B. cacuminata larvae but was more frequently visited, with greater parasitoid residency time and probing, when adult flies (either B. cacuminata or B. tryoni) were also present.
• 6 We conclude that herbivore‐induced, nonspecific host fruit wound volatiles were the major cue used by foraging D. krausii. Although positive orientation to infested host plants is well known from previous studies on opiine braconids, the failure of the wasp to orientate to some plants even when infested with physiologically suitable larvae, and the secondary role played by adult fruit flies in wasp host searching, are newly‐identified mechanisms that may aid parasitoid host location in environments where both physiologically suitable and unsuitable hosts occur.

     

Geographic variation in reproductive success of the parasitoid Asobara tabida in larvae of several Drosophila species

Abstract.

• 1 Asobara tabida is a parasitoid of Drosophila larvae in fermenting substrates. Because it is a widespread species, it may encounter different biotic and abiotic circumstances in various parts of its range.
• 2 The species composition of the host population varies over the parasitoid's range: D.obscura-group species (especially D.subobscura) are the main hosts for northwestern and central European parasitoids; D.melanogaster is the main host for southern European parasitoids.
• 3 D.melanogaster larvae can defend themselves against A.tabida by encapsulating the parasitoid egg, and survival in D.melanogaster is always lower than in D.subobscura.
• 4 Parasitoids from southern European populations are much better able to survive in D.melanogaster than their northwestern and central European conspecifics; parasitoids from different populations are equally well able to survive in D.subobscura.
• 5 The lower survival in D.melanogaster may be partly compensated for by the larger size of parasitoids emerging from this host species compared to parasitoids emerging from D.subobscura.
• 6 Within population groups, larger A.tabida females have more eggs in their ovarioles. Additionally, southern European females have more eggs and less fat than northern and western/central European females. The relationship between size and longevity is ambiguous.
• 7 It is concluded that parasitoids from different populations are adapted to region-specific circumstances.

     

Chironomus species (Diptera: Chironomidae) in the profundal benthos of Spanish reservoirs and lakes: factors affecting distribution patterns

• 1 The taxonomy, distribution and habitat preferences of Chironomus larvae from profundal benthos of reservoirs and natural lakes in Spain are presented. The 114 water bodies studied were medium to large reservoirs and lakes throughout Spain, and were visited on at least two occasions (summer and winter). Out of the natural lakes investigated, Chironomus larvae were found only in one karstic lake (Banyoles), and to date, these have not been found in the high mountain lakes of the Spanish Pyrenees or Sierra Nevada, or in Spain's largest oligotrophic lake (Sanabria).
• 2 Multiple regression with environmental data from reservoirs showed that the density of Chironomus larvae was inversely correlated with water depth, temperature and sulphide content of the bottom water, but positively correlated with alkalinity and particulate organic nitrogen (PON) content of bottom water. Thus, the density of Chironomus larvae was higher in shallow reservoirs from the eastern part of Spain (calcareous water and higher PON), but markedly lower in southern reservoirs (higher temperature and higher sulphide).
• 3 According to morphological and cytological characteristics, three species of this genus have been identified in the samples examined: C. bernensis, C. plumosus and C. nuditarsis. Reasons for the absence of other widespread European species are discussed.
• 4 Using canonical correspondence analysis to relate species and environmental variables, C. bernensis showed a significant preference for reservoirs with higher oxygen concentrations in bottom water and lower total reactive phosphorus (TRP) content at the surface than those reservoirs where C. plumosus‐type were found. This suggests that the smaller C. bernensis prefers mesotrophic reservoirs and the larger C. plumosus‐type (C. plumosus + C. nuditarsis) prefers eutrophic reservoirs. Taking into account the TRP/depth index for those samples collected at depths below the thermocline, and thus, where oxygen can be a limiting factor, C. bernensis and C. nuditarsis were present in reservoirs in which the index was low (< 1:170 for C. bernensis and >1:800 for C. nuditarsis), while C. plumosus thrived in reservoirs with higher index values (<1:20). These differences may reflect the preference of C. bernensis and C. nuditarsis for detrital material, while C. plumosus prefers phytoplankton. These observations are in agreement with the depth distribution of each species: C. plumosus was restricted to reservoirs less than 46 m deep, whereas the other two species (i.e. C. bernensis and C. nuditarsis) were found up to depths of 65 and 80 m, respectively.
• 5 Data from a transect (5–20 m deep) in Lake Banyoles are consistent with the general pattern described in reservoirs. In this lake, a high density of C. bernensis was recorded from littoral and sublittoral areas with abundant oxygen (above or close to the thermocline), whereas C. plumosus was scarce in several parts of the lake, especially in oxygen‐deficient areas during the summer. This karstic, oligotrophic lake has a low TRP/depth index, and therefore, we expected C. bernensis to be dominant in the littoral, as is the case. Nevertheless, the severe depletion of oxygen caused by meromixis, and the high hydrogen sulphide concentration benefit C. plumosus in deeper zones. Chironomus nuditarsis was scarce in Lake Banyoles and only found at considerable depths.

     

Spatiotemporal distribution of the hemlock woolly adelgid predator Laricobius nigrinus after release in eastern hemlock forests

• 1 Post‐release distributions of Laricobius nigrinus, a biological control predator of hemlock woolly adelgid Adelges tsugae Annand, were evaluated at eight hemlock forests in the eastern U.S.A.
• 2 Vertical dispersal of F₁ and F₂L. nigrinus were assessed from within three crown strata (<7, 7–15 and >15 m) at four release sites.
• 3 Horizontal distributions of L. nigrinus within the forest surrounding central release areas were observed in two separate studies, which included (i) release and monitor to capture parent and F₁ movement by sampling the immature life stages of the offspring, and (ii) assessment of F₃ to F₆ generations where beetles were previously determined to be established.
• 4 Laricobius nigrinus, released on lower crown branches, oviposited within the upper crown stratum and were slow to disperse from release trees. Monitoring L. nigrinus only from the lower crown would likely underestimate its presence because 86% of the F₂ generation were detected above 15 m.
• 5 By the fifth generation, the frequency distributions of larvae increased at increasing distance from release areas; larvae were recovered at a maximum distance of approximately 400 m and the spread rate was approximately 39 m/year.
• 6 Slow dispersal of L. nigrinus and uninterrupted recovery of six generations in the presence of fluctuating prey density support its continued release as part of the A. tsugae biological control programme. These data contribute toward improved release strategies and monitoring for this biological control agent.