The impact of a small, alien invertebrate on a sub-Antarctic terrestrial ecosystem: Limnophyes minimus (Diptera, Chironomidae) at Marion Island

Density and biomass of the larvae of a small, alien chironomid midge, Limnophyes minimus, whose parthenogenetic adult females do not feed, were quantified for ten major lowland plant communities at sub-Antarctic Marion Island (46°52′S 37°51′E) and compared with the density and biomass of indigenous macro-invertebrates in the same communities. An estimate of litter consumption by larvae of this midge was also made. L. minimus reached high densities in most of the plant communities sampled, with the highest density being recorded in the Cotula plumosa biotically influenced community (annual mean of 4,365 individuals m⁻²) and the lowest in the Crassula moschata salt spray community (annual mean of 41 individuals m⁻²). Estimates of litter ingestion indicated that L. minimus larvae are capable of consuming between 0.07 and 8.54 g_{(dry mass)} m⁻² per year, depending on the community. In some communities this litter consumption amounted to an order of magnitude more than that consumed by Pringleophaga marioni (Lepidoptera, Tineidae). Although the larvae of this moth species are thought to represent the bottleneck to nutrient recycling on the island, this study showed that midge larvae may also contribute substantially to this process. As a consequence, the considerable changes that have been predicted to occur in Marion Island's terrestrial ecosystem as a consequence of enhanced predation by mice on P. marioni larvae may be retarded or obscured by the contribution of the midge larvae to nutrient cycling. Hence, it is suggested that greater attention be given to the small and inconspicuous elements of the alien sub-Antarctic faunas because such species may have profound consequences for ecosystem functioning on these islands. Received: 17 November 1997 / Accepted: 23 February 1998     

Effects of insect damage on photosynthesis,transpiration and SO2 uptake by sycamore

Summary The bilberry (Vaccinium myrtillus L.), is the dominant plant in the field layer of many boreal forests in northern Sweden. It is utilized by several herbivorous insect larvae as food (i.e. Lepidoptera: Geometridae, Tortricidae and Hymenoptera: Symphyta). Total density of insect larvae was 63% lower where birds had access to larvae compared to exclosures. Larvae with a feeding behaviour which exposes them to birds (geometrids and sawflies) showed a pronounced reduction in density when exposed to bird predators. Density of larvae with a concealed feeding behaviour (tortricids) was unaffected by birds. The frequency of larval damage to bilberry annual shoots was significantly higher in areas where larval density was high due to exclusion of birds. I concluded that birds have the potential to heavily modify the interaction between bilberry and insect larvae.     

Annual Changes in the Greater Wax Moth (Galleria Mellonella L.) Development and Sensitivity to Juvenilizing Treatments

The greater wax moth (Galleria mellonella L.) larvae reared in constant conditions showed endogenous annual changes in the sensitivity to juvenilizing treatments, i.e. cooling and JHA administration. Also control, untreated larvae showed annual changes in normal development. The number of spontaneously appearing extra-larval molts, the number of animals entering the state of permanent larva, as well as the sex-ratio in Galleria population changed with respect to the season of the year. The possible mechanisms involved in these phenomena are discussed.     

Feeding and fate of wild larval razorback sucker

The razorback sucker (Xyrauchen texanus) is disappearing throughout its native range in the Colorado River basin of western North America. The largest remaining wild population in Lake Mohave, Arizona-Nevada, has shown no recruitment since the 1950s. Although annual spawning is successful and larvae are seasonally abundant, no juveniles have been collected in recent decades. To evaluate the potential role of food availability in determining fate of larvae, fish and zooplankton samples were taken in 1985 from the reservoir and an adjacent, isolated backwater in which larvae were naturally produced. Food availability and primary dietary constituents were similar in both habitats. Reservoir larvae selectedBosmina spp. (Cladocera) and apparently avoided Copepoda, while larvae from the backwater selectedBosmina, but avoided Rotifera. Larvae from both places showed evidence of selection for certain sizes of zooplankters, but preferred sizes differed between habitats. These differences were neither attributable to larval size nor zooplankton community structure. Nutritional factors such as type, number, or size of available foods do not explain disappearance of larval razorback suckers from Lake Mohave, since larvae survive to far greater ages and size in the backwater. Predation by introduced fishes appears a significant cause of larval mortality.     

New method for rapidly estimating population densities of the concealed wood‐borer Monochamus alternatus (Coleoptera: Cerambycidae) in the field

To rapidly estimate pine sawyer, Monochamus alternatus Hope, population densities in forests, the vertical distributions of M. alternatus oviposition sites and larvae on infested Masson pines (Pinus massoniana Lamb.) were studied. Results showed that the number of oviposition sites on sections of trunks between 0 and 2 m above ground was significantly greater than on sections of trunk above 2 m, and the vertical distribution had a significant logarithmic relationship with trunk height. The larval number of M. alternatus on dead infested trees had a significant difference among heights of trunks. Sections on trunks at 2–4 m usually contained the largest number of M. alternatus larvae, while the number of larvae on trunks above 10 m declined significantly, as well as in the 1 m section of trunk at the base. The vertical distribution of M. alternatus larvae on dead infested pines showed a distinct parabolic relationship with trunk height. The number of oviposition sites of M. alternatus on infested Masson pine trunks revealed a significant exponential relationship with the diameter at breast height (DBH) of trees. A significant positive linear relationship also was observed between M. alternatus larval number and DBH on the host pine trees, as well as between the numbers of larvae and oviposition sites on an individual tree. The total number of larvae in an infested tree could be calculated easily using an established equation, through counting the number of oviposition sites at 3–4 m of trunk aboveground. This study developed a practical method for rapid estimation of M. alternatus populations.     

Distribution and production ofChironomus salinarius (Diptera: Chironomidae) in a shallow coastal lagoon in the Bay of Cádiz

The abundance, generation time and production ofChironomus salinarius larvae in a lagoon fish-pond system in the Bay of Cádiz were studied by taking monthly samples at 3 sites during 1991 and 1992. Numerical abundance and biomass of larvae showed considerable spatial, seasonal and interannual variation (ANCOVAs,P<0.001). The maximum mean annual density was 7048 larvae m^–2, and corresponded to a biomass of 3.08 g dry weight (DW) m^–2. It was recorded at the site with the lowest rate of water renewal. Seasonal patterns were similar at all sites, with main annual peaks of abundance and biomass in autumn-early winter. Chironomid density was positively related to the biomass of benthic macroalgae (P<0.001). The population studied was multivoltine with a probable average of five generations per year, with overlapping cohorts and a predominance of third- and fourth-instar larvae. Estimates of annual production ranged between 72.2 g DW m^–2 yr^–1 at the site with the lowest rate of water renewal in 1991 and 0.1 g DW m^–2 yr^–1 at the site with the highest rate of water renewal in 1992. Mean annual production and the production/biomass ratio for the system was estimated to be 16.8 g DW m^–2 yr^–1 and 12.7, respectively. Possible factors leading to the observed density fluctuations are discussed, as well as possible sources of error in production estimates.     

Microplitis croceipes teratocytes cause developmental arrest of Heliothis virescens larvae

Microplitis croceipes teratocytes placed into nonparasitized Heliothis virescens larvae survived in the absence of a parasitoid larva and caused developmental changes in the host. Expressions of these changes included delayed larval mortality, incomplete larval-pupal ecdysis, or delayed pupation. Two day old 4th stadium H. virescens larvae were more sensitive to injected teratocytes than were 5th stadium larvae. Three day old teratocytes were more effective than were 6 day old teratocytes. The degree of response was related to the number of injected teratocytes. For example, 750 three day old teratocytes (the approximate number from a single parasitoid egg) caused delayed larval mortality in 96% of the treated larvae whereas 175 three day old teratocytes caused delayed larval mortality in only 33% of the treated larvae. Even a dose of 80 teratocytes resulted in 15% incomplete larval-pupal ecdysis compared to 0% for controls. Treatment with hemocyte-and teratocyte-free hemolymph from parasitized larvae, hemocytes from nonparasitized H. virescens, unfertilized M. croceipes eggs, Cotesia congregata teratocytes, or Micrococcus lysodeikticus cells all had very little effect either on larval growth or development time.     

Impact of Embryonopsis halticella eaton larvae (Lepidoptera: Yponomeutidae) feeding in Marion Island tussock grassland

Summary Embryonopsis halticella is a brachypterous moth endemic to the Kerguelen Province of sub-Antarctic islands. Its larvae are strictly host-specific grass-borers of the tussock grass Poa cookii, and are the major herbivores on Marion Island. Monthly sampling over one year (1984) on Marion Island showed that E. halticella larvae reach a biomass of 0.222 g m^-2 (dry mass) in P. cookii grassland in summer. In feeding experiments conducted in the laboratory on Marion Island, larvae consumed 0.3 X their own live mass in leaf material daily. Extrapolated consumption rates in the field range from 1 kg ha^-1 month^-1 in winter to 18 kg ha^-1 month^-1 (dry mass) in summer. Total annual consumption, based on leaf feeding only, amounts to 86 kg ha^-1 (dry mass). Significant shifts in diet from foliage to seeds occur during spring, and larvae also consume their own frass and exuviae. It is calculated that E. halticella larvae remove 2.5% of the annual production of Poa cookii in Marion Island tussock grassland.     

Changes in the reproductive biology of Biomphalaria glabrata experimentally infected with the nematode Angiostrongylus cantonensis

This study showed for the first time changes in the reproductive biology of Biomphalaria glabrata experimentally infected with Angiostrongylus cantonensis. The values of all the parameters analyzed (total number of eggs, number of egg masses, number of eggs/mass, number of eggs/snail, percentage of viable eggs and galactogen content in albumen gland) changed with progressive infection. The results indicate the occurrence of partial parasitic castration of B. glabrata by A. cantonensis larvae, probably in response to the depletion of energy reserves, with no injuries to the gonadal tissues.     

Ant benefits in a seed dispersal mutualism

Myrmecochorous plant seeds have nutrient rich appendages, elaiosomes, which induce some ant species to carry the seeds back to their nest where the elaiosome is consumed and the seed is discarded unharmed. The benefits to plants of dispersal of their seeds in this way have been well documented, but the benefits to the ants from consuming the elaiosomes have rarely been measured and are less clear. Ant benefits from myrmecochory were investigated in a laboratory experiment using the ant Myrmica ruginodis and seeds of Ulex species. To separate the effects of elaiosome consumption on the development of newly produced larvae versus existing larvae, ten ‘Queenright’ colonies containing a queen were compared to ten ‘Queenless’ colonies. Six measures of colony fitness over a complete annual cycle were taken: sexual production, larval weight and number, pupal weight and number, and worker survival. Queenless colonies fed with elaiosomes produced 100.0±29.3 (mean ± SE) of larvae compared to non-elaiosome fed colonies which produced 49.6±19.0; an increase of 102%. Larval weight increased in both Queenright and Queenless colonies. In colonies fed with elaiosomes, larvae weighed 1.02±0.1 mg, but in non-elaiosome fed colonies larvae weighed 0.69±0.1 mg; an increase of 48%. The food supplement provided by Ulex elaiosomes was trivial in energetic terms, under the conditions of an ample diet, suggesting that these effects might be due to the presence of essential nutrients. Chemical analysis of Ulex elaiosomes showed the presence of four essential fatty acids and four essential sterols for ants.     

IMPACT OF IMMUNE RESPONSE OF A PARASITIC BEETLE Dastarcus helophoroides ON ITS HOST BEETLE Monochamus alternatus

Dastarcus helophoroides is an ectoparasitoid beetle of Monochamus alternatus, and the parasitism by D. helophoroides larvae remarkably influenced on the immune responses of M. alternatus larvae in many aspects. The hemolymph melanization reactions in the hosts were inhibited 1 h and 24 h postparasitization. The phenoloxidase activities of hemolymph were significantly stimulated 4 h postparasitization and inhibited 12 h postparasitization, and back to control level. The antibacterial activities of hemolymph in the parasitized hosts were significantly lower than that in the unparasitized ones 1 h postparasitization. By 72 h postparasitism, the total hemocyte numbers of the parasitized larvae declined to not more than one‐seconds of the number collected from the unparasitized larvae. All sampled hemolymph held the capability of nodulation, and there were fluctuations in the number of nodules the hemocytes made. However, there were no significant differences between unparasitized and parasitized larvae at each time point in the hemagglutination activity and the ratios of spreading hemocytes. In conclusion, D. helophoroides larvae could regulate M. alternatus immune system and resulted in the changes in host immune responses.     

A comparison of swimming structures and kinematics in three species of crustacean larvae

Crustacean larvae swim with paired rowing appendages that rotate around the body of the animal. The number of paired rowing appendages varies from one species of larvae to another. In addition, the size of the crustacean larvae is different between species and increases as they grow. The nature of the fluid forces changes as size increases, so the morphology and mechanics of swimming in these animals will change during increases in size. This article demonstrates the changing kinematics of locomotion between three species of crustacean larvae, which swim with one (Artemia franciscana), two (Carcinus maenas) or five (Homarus americanus) pairs of propulsive limbs. The relative change in the surface area and volume ratios of the locomotor structures are also demonstrated.     

Susceptibility of Meligethes spp. and Dasyneura brassicae to entomopathogenic nematodes during pupation in soil

The susceptibility of pupating larvae of pollen beetles, Meligethes spp. Stephens (Coleoptera: Nitidulidae) and brassica pod midges, Dasyneura brassicae Winnertz (Diptera: Cecidomyidae) to entomopathogenic nematodes (Nematoda: Rhabditida) was studied in the laboratory. The results showed that brassica pod midge larvae were almost unaffected by the tested nematodes (Steinernema bicornutum, S. feltiae and Heterorhabditis bacteriophora) whereas successful pupation of pollen beetle larvae was reduced with increasing number of nematodes (S. bicornutum, S. carpocapsae, S. feltiae and H. bacteriophora). The exposed larvae had been collected in the field and some of the pollen beetle larvae were parasitised by parasitoid wasps. It appeared that parasitised larvae were less affected by nematodes than non-parasitised larvae.     

长江口水域夏季鱼卵和仔稚鱼年间变化

基于2005年、2008年、2009年和2011年8月(夏季)在长江口水域(30°30'—31°45'N,121°15'—123°10'E)4个航次的浮游生物拖网资料,分析了长江口水域鱼卵和仔稚鱼的种类组成、数量分布特征及其年间变化。结果表明:4个航次采集的鱼卵和仔稚鱼鉴定到种的种类有17种,隶属于8目13科,以鲈形目种类最多,11种,其次是鲱形目,5种,其他各目种类均小于5种;种类数存在明显年间差异,2005年种类数最多(鱼卵3种,仔稚鱼8种),其次是2009年和2011年,2008年种类数最少(鱼卵1种,仔稚鱼5种)。优势种年间更替明显,长蛇鲻(Saurida elongata)、虾虎鱼(Gobiidae spp.)和中华小公鱼(Stolephorus chinensis)在2005年是优势种,2008年优势种为鳀鱼(Engraulis japonicus),2009年优势种为鳀鱼、寡鳞飘鱼(Pseudolaubuca engraulis)、虾虎鱼等,2011年虾虎鱼和小公鱼(包括小公鱼属未定种Stolephorus spp.和中华小公鱼Stolephorus chinensis)成为优势种。2005年鱼卵和仔稚鱼数量分布的密集区在嵊泗列岛附近水域,2008年鱼卵和仔稚鱼出现较少,未出现明显的数量密集区;2009年鱼卵数量较少,仔稚鱼数量较多,密集区主要分布在在长江口以外123°E附近水域;2011年鱼卵主要分布在在长江北支口门外附近水域,仔稚鱼在调查区内分布相对均匀。     

Polymorphic growth in larvae of Maculinea butterflies, as an example of biennialism in myrmecophilous insects

The presence of annual and biennial individuals within the same population has been recently demonstrated in the myrmecophilous butterflies Maculinea rebeli and Maculinea alcon, which present a cuckoo strategy inside Myrmica nests, and Maculinea arion which is a predatory species. Here, we present field and laboratory data on polymorphic larval growth in two other predatory species of Maculinea: M. teleius and M. nausithous. Body mass distributions of pre-pupation larvae were bimodal in both species. These results point to the existence of larvae that develop in 1 or 2 years. We also showed that the probability of pupation depended on larval body mass. In the case of M. teleius, the critical body mass at which larvae have a 50% probability of pupation is about 80 mg. We suggest that polymorphism in Maculinea may have evolved as an adaptation to life in ant nests, a habitat which protects them from predators and provides food. However, the quality of this resource is highly variable and unpredictable. According to the bet-hedging hypothesis, if the habitat is unpredictable, females should have an advantage by producing more variable offspring. In the case of Maculinea butterflies, this may involve maintaining larvae that develop in 1 or 2 years.     

Influence of sea temperature and initial marine feeding on survival of Atlantic salmon Salmo salar post-smolts from the Rivers Orkla and Hals, Norway

The abundance of returning adult Atlantic salmon Salmo salar, in the River Orkla in mid‐norway (1 sea‐winter, SW, fish) and River Hals in north Norway (1–3 SW fish), was tested against the early marine feeding and the seawater temperature experienced by their corresponding year classes of post‐smolts immediately after entry into the Trondheimsfjord (Orkla smolts, 22 years of data) and Altafjord (Hals smolts, 17 years of data). In both river–fjord systems, there was a significant positive correlation between the abundance of returning S. salar and the mean seawater temperature at the time of smolts descending to the sea. The number of 1SW fish reported caught in River Orkla was positively correlated to the proportion of fish larvae in the post‐smolt stomachs in Trondheimsfjord. The abundance of returning S.salar was, however, neither correlated to forage ratio (R_F) nor other prey groups in post‐smolt stomachs in the two fjord systems. In the Altafjord, the post‐smolts fed mainly on pelagic fish larva (70–98%) and had a stable R_F (0·009–0·023) over the 6 years analysed. In the Trondheimsfjord, however, there was a higher variation in R_F (0·003–0·036), and pelagic fish larvae were dominant prey in only two (50 and 91%) of the 8 years analysed. These 2 years also showed the highest return rates of S. salar in River Orkla. These results demonstrate that the thermal conditions experienced by post‐smolts during their early sea migration may be crucial for the subsequent return rate of adults after 1–3 years at sea. Pelagic marine fish larvae seem to be the preferred initial prey for S. salar post‐smolts. As the annual variation in abundance of fish larvae is related to seawater temperature, it is proposed that seawater temperature at sea entry and the subsequent abundance of returning adult S. salar may be indirectly linked through variation in annual availability of pelagic fish larvae or other suitable food items in the early post‐smolt phase.     

褐梗天牛幼虫和成虫空间分布的地统计学研究

褐梗天牛(Arhopalus rusticus Linnaeus)是一种对松、杉、柏等林木危害非常严重的蛀干害虫,主要危害针叶树的衰弱木以及火灾后的枯立木,是继松褐天牛之后携带拟松材线虫能力最强的蛀干害虫。为了更好地控制其危害,深入地研究其种群空间格局,运用地统计学方法分析了3块受害程度不同的油松林内褐梗天牛幼虫和成虫的空间分布特性。结果表明:3种受害程度不同的林分内,褐梗天牛的危害具有显著差异,轻度受害林分内有虫株率为30.8%,中度受害林分内有虫株率为44.3%,而重度受害林分内高达78.3%。根据变异函数曲线图分析得知:轻度受害林、中度受害林和重度受害林内褐梗天牛幼虫种群空间分布最优拟合模型分别为高斯模型、高斯模型和指数模型,成虫的种群空间分布最优拟合模型均为线性模型。在3种林分中褐梗天牛幼虫数量具有明显的空间依赖性,轻度受害林、中度受害林和重度受害林内幼虫数量的空间依赖范围分别是19.10、11.97、61.98m,其空间连续性强度分别是0.646、0.784和0.500;成虫的空间依赖范围分别是43.08、43.23、44.17m,其空间连续性强度分别是0.044、0.021和0.171,但其成虫的数量在空间呈随机分布,没有表现出空间依赖性。根据垂直分布图分析得出:褐梗天牛幼虫和成虫在油松上主要集中聚集在某个高,然后随着高度增加密度降低,随着高度接近地面密度也降低。用Kriging插值法生成的空间分布图显示幼虫在空间分布上具有明显的聚集性,其聚集中心主要集中在林地中心,由林地中心株向整个林地扩散,而成虫则表现为随机分布。     

Seasonal changes in the stable isotope values of lake-dwelling chironomid larvae in relation to feeding and life cycle variability

1. We studied seasonal changes in the carbon and nitrogen stable isotope ratios of larval Chironomus anthracinus and C. plumosus from the profundal sediments of four contrasting lakes. 2. Pronounced seasonal changes in both δ¹³C and δ¹⁵N values were evident in chironomid larvae of both species from two summer‐stratified, eutrophic lakes: Esthwaite Water and Wyresdale Park. Changes were most marked in the larvae of C. plumosus and in larvae from greater depths. In contrast, neither C. anthracinus in summer‐stratified but mesotrophic Schöhsee, nor C. plumosus in polymictic Großer Binnensee, showed marked seasonality in larval stable isotope ratios. 3. The particularly strong ¹³C‐depletion of larvae from the stratified, eutrophic lakes is attributed to a significant contribution of methane‐derived carbon to their diets. Feeding by larvae on isotopically light methanotrophic bacteria appears to occur mainly when autumn overturn of the water column restores oxygenated conditions to the sediment surface. At this time both δ¹³C and δ¹⁵N values of larvae decreased sharply. 4. Changes in the mean stable isotope ratio of the larval populations can also occur when larger, more isotopically light, larvae pupate and emigrate from the population to hatch as imagos. This effect can induce seasonal changes in larval isotope values even in lakes in which there is no evidence of a significant involvement of methane‐derived carbon in their diets. Variations in emergence patterns between species and between lakes may generate differences in the seasonal pattern of change in stable isotope ratios in larval populations. 5. Our results emphasise the importance of adequate seasonal sampling if stable isotope ratios are to be used as biomarkers to study the role of key groups, such as chironomid larvae, in the trophic structure of lakes.     

Environmental influences on prolactin cell development in the cyprinodont fish,Cynolebias whitei

Summary A combined immunocytochemical and morphometric study on the development of the prolactin (PRL) cells of the annual cyprinodont Cynolebias whitei, transferred as newly hatched larvae to water with different salinities and/or Ca²⁺-concentrations, was carried out. The percentage of the pituitary volume occupied by PRL cells and the affinity of PRL cells for immunocytochemical staining were used as criteria for their activity. Exposure of the larvae for one day to salt water (260 mOsm/kg) led to a significant reduction in the pituitary volume occupied by PRL cells, indicating an osmoregulatory function of PRL shortly after hatching. In fish reared in diluted artificial seawater (70 and 260 mOsm/kg) or Na⁺-enriched fresh water the development of PRL cells was significantly retarded, but such an effect was not observed in fish placed in Ca²⁺-enriched fresh water. These experiments show that in C. whitei the development and activity of PRL cells are influenced by changes in environmental osmolarity and not by changes in ambient Ca²⁺-concentration.     

Effects of gall volume on survival and fecundity of gall-making aphidsAdelges japonicus (Homoptera: Adelgidae)

The number of larvae reaching maturity within the gall of Adelges japonicus was positively related to gall volume, and the relationship between the number of mature larvae and gall volume did not change with different densities of colonized larvae. The population changes in the bud galls of A. japonicus were surveyed by collecting the galls, which did not suffer predation or parasitism within the galls, from young artificial plantations of Picea jezoensis over two years. In the year when the density of colonized larvae was high, they suffered a 42% mortality within the galls, whereas mortality was nearly zero in the low density year. The numbers of larvae per gall were positively correlated with gall volume. The regression lines of the number of colonized larvae on gall volume did not differ significantly in the regression coefficients between the two years, whereas the intercept was significantly higher in the year when the density of colonized larvae was higher. However, different within-gall mortality nullified this difference, and the regression lines of the number of mature larvae on gall volume had no significant difference both in the regression coefficients and the intercepts. This suggests that the number of mature larvae per gall was limited by available resources within the gall which were positively related to gall volume. In 25% of the galls in which mature larvae inhabited, the space within the galls were completely filled by the larvae, indicating that space was one of the limiting resources. Gall volume also affected the number of adults that emerged from the gall and the potential number of their progeny.