Respiratory metabolism of Hydromedion sparsutum and Perimylops antarcticus (Col., Perimylopidae) from South Georgia

Summary Metabolic rates were studied in adults and larvae of the two phytophagous beetles Hydromedion sparsutum and Perimylops antarcticus (Col., Perimylopidae) indigenous to the Sub-Antarctic island of South Georgia. From the regression lines for log₁₀ metabolic rate on temperature no difference in oxygen consumption was found between adults and larvae of Hydromedion or adults of Perimylops from lower sites near sea level and upper sites at about 200 m. Elevated rates of metabolism, however, was found in larvae of Perimylops from upper sites. The slopes of the regression lines of corresponding upper and lower sites adults or larvae were similar in all cases. The metabolic rates were of the same level in adults of both species and in the larvae, but generally higher in adults than in larvae. The activation energies, calculated from Arrhenius plots, varied from 6.7 to 13.6 kcal.mol^–1 in larvae and from 10.7 to 11.3 kcal.mol^–1 in adults. The low values may be interpreted as an expression of cold adapted metabolism. Compared with published data on phytophagous beetles, the metabolic rates of the two species from South Georgia are comparable to two alpine species, but lower than the rates of an Arctic species.     

青藏高原高寒草甸门源草原毛虫取食偏好及其与植物C、N含量的关系

草食性昆虫对不同植物物种的取食存在偏好,这种取食偏好可能受其自身对蛋白质和碳水化合物的需求及二者平衡的调节。以青藏高原高寒矮嵩草草甸31种常见植物及门源草原毛虫为对象,通过饲喂实验,研究了草食性昆虫对不同物种和不同功能群植物的取食偏好,及其与植物叶片C、N含量和C∶N之间的关系。在31种植物中,门源草原毛虫对19种植物进行了取食,尤其对矮嵩草、红棕薹草、藏异燕麦和垂穗披碱草四种植物表现出强烈的取食偏好,而对另外12种植物未进行任何取食。在物种水平上,门源草原毛虫取食量与植物叶片N含量呈显著负相关,与叶片C∶N呈正相关。从功能群水平上看,门源草原毛虫对莎草类的取食偏好最大,而对豆科植物取食偏好最低;相应地,莎草类植物叶片N含量最低、C∶N最高,而豆科植物叶片N含量最高、C∶N最低。因此,即使在土壤有效氮匮乏、植物生长受氮素限制的高寒草甸生态系统,植物体内N含量的增加也可能不利于草食性昆虫的取食。门源草原毛虫对优势植物矮嵩草和垂穗披碱草的取食对高寒矮嵩草草甸物种共存和生物多样性维持可能具有重要的作用。     

Larval consumption rates,interspecific predation,and local guild composition of egg-overwintering Agabus (Coleoptera,Dytiscidae) species in vernal ponds

Summary In vernal ponds in the boreal region, egg-over-wintering Agabus species form a guild that feeds mainly on larvae and pupae of aedine mosquitoes. The regular co-existence of very similar Agabus species indicates local communities not structured by interspecific competition. However, the lower number of species in local guilds than in the regional species pool poses a problem of limited membership. We suggest that the species of this guild display habitat differences mainly with respect to water temperature, pond size and prey density. In this view, habitat selection reflects body size and thermal growth response of the species, mainly in connection with larval development. We present field data from two northern Swedish vernal ponds. Based on these data, feeding experiments were performed to test the hypothesis outlined above. At a high prey density, larvae of all instars of the larger species A. erichsoni Gemm. & Har. had a significantly higher consumption rate than those of the smaller species A. opacus Aubé. At a low prey density the differences were smaller, and only the third instar larvae differed significantly. At 2° C, larvae of A. opacus had a significantly higher consumption rate than those of A. congener (Thunberg). At 15° C, no significant difference was observed. In studies of within-guild interspecific predation, always the larger larvae consumed the smaller ones. Field data show that egg hatching is spread out in time, and show interspecific differences. Consequently, the effects of unexpected droughts differ with species.     

Predation by three hemipterans:Tropiconabis nigrolineatus,Oechalia schellenbergii andCermatulus nasalis,onHeliothis punctiger larvae in two types of searching arenas

Three species of hemipteran predators preyed differently upon 1^st instarHeliothis punctiger Wallengren larvae.Cermatulus nasalis consumed more larvae thanOechalia schellenbergii which consumed more larvae thanTropiconabis nigrolineatus. All the species consumed significantly less 1^st instar larvae on plants than what they consumed in Petri-dishes. Fifth instar predators showed significant differences in terms of prey consumption due to sex independent of searching conditions. Only 4^th and 5^th instars ofT. nigrolineatus attacked and captured 2^nd instars ofH. punctiger larvae. The other 2 species however readily attacked and consumed 2^nd instarH. punctiger larvae. Their prey consumption was similar in Petri-dishes and on plants. Only 5^th instars ofT. nigrolineatus could subdue and capture 3^rd instarH. punctiger larvae. Second instar pentatomids captured just one 3^rd instar larva but older instars killed and ate more. Fourth instarH. punctiger larvae were immune to attacks by allT. nigrolineatus and younger pentatomids due to their defense ploys but 5^th instar pentatomids could subdue and capture them. None of the predators captured 5^th instarH. punctiger larvae except few 5^th instar females ofC. naslis andO. schellenbergii.      

Partitioning of food resources among Sillago japonica, Ditremma temmincki, Tridentiger trigonocephalus, Hippocampus japonicus and Petroscirtes breviceps in an eelgrass, Zostera marina, bed

We carried out dietary analysis on five numerically abundant fishes, Sillago japonica, Ditremma temmincki, Tridentiger trigonocephalus, Hippocampus japonicus and Petroscirtes breviceps in an eelgrass bed in Kwangyang Bay, Korea. Comparisons between species demonstrated that the dietary composition of each fish species was significantly different from that of every other species. Although gammarid amphipods and caprellid amphipods were consumed by all species, their individual contributions to each species' diet varied. Furthermore, polychaetes contributed to the diets of S. japonica and T. trigonocephalusand crab larvae were consumed byD. temmincki. Algae and eelgrass were not consumed by four fish species and made only a minimal contribution to the diet of P. breviceps. The diet of each fish species except H. japonicus underwent size-related changes; smaller fishes consumed gammarid amphipods, mysids and copepods, while larger fishes ate polychaetes, gastropods, isopods and other fishes. Differences in the prey organisms consumed of each individual species could be often related to differences in mouth length and width. S. japonica, D. temmincki, T. trigonocephalus, and P. breviceps underwent also a significant diel changes that could be related to differences in foraging behavior and/or prey availability. Thus, use of vision to detect prey would account for the greater daytime consumption of copepods by S. japonica and of crab larvae by D. temmincki, whereas the nocturnal emergence of gammarid amphipods, polychaetes and isopods from the substrate explained their greater consumption by S. japonica, D. temmincki, T. trigonocephalusand P. breviceps at night. Dietary breadth was greater for species with larger mouth dimensions.     

Body water content and desiccation resistance in some arthropods from subantarctic South Georgia

Summary The body water content and resistance to desiccation were studied in two perimylopid beetles, Perimylops antarcticus and Hydromedion sparsutum, a chironomid midge, Eretmoptera murphyi, and two spiders, Notiomaso australis and Perimaso grytvikensis from the subantarctic island of South Georgia. Comparisons were made between different species, different life stages and, where possible, between a high and a low altitude. Perimylops is abundant at higher elevations and in more exposed habitats (fellfields). This may be accounted for by its feeding behaviour, high body water content (relative to Hydromedion) and low rate of water loss under desiccating conditions, particularly in the larval stages. Hydromedion is more abundant at the lower collection site. It is a more robust beetle than Perimylops and its feeding preference is for plants such as grasses and Acaena. Nevertheless, at the upper site adult Hydromedion are able to withstand desiccation to an even greater degree than Perimylops. Water loss rates for both beetles are significantly higher than those reported for related beetles from arid and semi-arid regions. The ability to regulate water loss is not as apparent in the polar perimylopids Perimylops and Hydromedion as in related species from other xeric habitats. These two species, in fact, resemble more closely carabid beetles in xeric habitats in rates of water loss under controlled conditions. Increased temperatures elevate the rate of water loss significantly. South Georgia spiders have a similar rate of water loss to several species of spiders that have been studied in the temperate zone. Eretmoptera is restricted to moist conditions and cannot survive desiccating conditions even for brief periods. It has the highest body water content (78% of fresh weight) of all of the South Georgian arthropods studied. Among the spiders, sufficient information could be obtained only for Notiomaso. This species is much less resistant to desiccation than the perimylopid beetles, and it has a relatively high body water content. It is quite numerous in the lower, warmer habitats where its insect prey is more abundant and diverse.     

Feeding ecology of the vulnerable aoudad (Ammotragus lervia) in north-western Sahara

The feeding ecology of the aoudad (Ammotragus lervia) was investigated for the first time in north-western Sahara, Djebel Antar (Bechar province, Algeria), from autumn 2015 to summer 2016. Microhistological analyses of faeces revealed an annual diet composed of 23 identified taxa belonging to 16 plant families. The highest species diversity was recorded in spring and summer (23 species), despite a marked consumption of two species: Vachellia tortilis (17.7%) and Avena sterilis (14.0%); diet diversity was lower in autumn and winter (16 species), including mainly Teucrium polium (14.7%, 21.0%) and Gymnocarpos decander (19.7%, 10.0%). The main plant parts consumed during these seasons were stems (77.7%, 65.3%), while leaves and inflorescences were mostly consumed during spring and summer (54.7%, 52.3%). Forbs dominated the aoudad's diet, with 46.3% average relative abundance, including mainly T. polium, Limoniastrum feei, and Chrysanthemum macrocarpum. Woody plants including mainly V. tortilis and G. decander accounted for 33.3% (50.0% in autumn), and grasses including A. sterilis and H. murinum for 20.4% (32.0% in summer). Based on this diet, A. lervia can be classified as a “generalist mixed-feeder.”     

Bryophytes as food: comparative consumption and utilization of mosses by a generalist insect herbivore

Compared with angiosperms, bryophytes are seldom fed upon by insects, despite being commonly used for shelter. Bryophytes are assumed to be unpalatable, and three classes of mechanisms have been suggested as possible barriers to bryophagy: chemical defenses, low digestibility, and low nutrient content. However, very few studies have tested these hypotheses. The present study examines pre‐ and post‐ingestive defenses of mosses. The acceptability and quality of four species of moss –Bryum argenteum Hedw. (Bryales: Bryaceae), Climacium americanum Brid. (Leucodontales: Climaciaceae), Leucobryum glaucum (Hedw.) (Dicranales: Leucobryaceae), and Sphagnum warnstorfii Russ. (Sphagnales: Sphagnaceae) – were compared with two control diets using the generalist caterpillar, Trichoplusia ni Hübner (Lepidoptera: Noctuidae: Plusiinae). In no‐choice trials, caterpillars consumed much less of any of the mosses than lettuce or wheat germ. The only moss consumed in sufficient quantities to evaluate post‐ingestive responses was C. americanum. Digestibility, assimilation, and overall utilization efficiency of C. americanum did not differ from that of lettuce, although C. americanum and lettuce were both less digestible than artificial diet. Choice assays using leaf discs showed that ethanol extract of L. glaucum, the least consumed moss, was deterrent, implying that chemical defenses play a major role in deterring feeding on L. glaucum. This study suggested that pre‐ingestive mechanisms are more important than post‐ingestive mechanisms in discouraging herbivory on mosses, and offered evidence that mosses are not simply nutrient poor.     

Relative consumption of three aphid species by the lacewing, Chrysoperla rufilabris, and effects on its development and survival

Relative consumption of three aphid species, Aphis gossypii Glover, Myzus persicae (Sulzer) and Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae), by larvae of the lacewing, Chrysoperla rufilabris (Burmeister) (Neuroptera: Chrysopidae), was determined in the laboratory, together with effects on lacewing development and survival. Percentages of survival of C. rufilabris from first instar to adult eclosion were significantly different among lacewing larvae fed different aphid species. When larvae were fed A. gossypii and M. persicae, all larvae developed to adulthood. All larvae died prematurely when they were fed L. erysimi. Developmental duration of C. rufilabris larvae was significantly shorter when larvae were fed A. gossypii (18.0 d) than when larvae were fed M. persicae (19.2 d). The number of fourth instar aphids consumed during development by C. rufilabris larvae differed significantly among individuals fed different aphid species. Chrysoperla rufilabris consumed an average of 168 M. persicae, followed by 141.6 A. gossypii, and only 26.6 L. erysimi. The percentage of these total number of aphids consumed by each larval stadium of C. rufilabris varied significantly among aphid species. The percentage of A. gossypii consumed by each larval stadium was similar to that for M. persicae, 12.1 and 11.4% by the first instar, 15.7 and 13.1% by the second instar, and 72.2 and 75.5% by the third instar, respectively; whereas in the case of L. erysimi, 23.3% of the total number of aphids were consumed by the first instar, 30.1% by the second instar, and 46.6% by the third instar.     

Food selection in <Emphasis Type="Italic">Microtus arvalis</Emphasis>: the role of plant functional traits

We offered captive common voles (Microtus arvalis) a choice of 11 plant species (representing four ecological groups) growing in vivaria. Selection was evaluated by measuring (1) the biomass of each plant species consumed and (2) functional and life-history plant traits. The legume Trifolium pratense, known for its high nutrient level, and well accessible rosette forbs creating the highest biomass at the soil ground level, were mostly preferred. Voles avoided mainly grasses and the creeping forb Thymus pulegioides. The experiment showed that foraging was strongly plant species-specific. We assessed whether plant functional traits explain selective foraging in common voles. To explore this, we reanalyzed Holišová’s (1959) data about common vole stomach contents and plant trait databases. Regression tree analysis indicated that plant guild and life span were the best predictors of dietary selection, with a probability exceeding 0.5 that voles would eat more grasses and/or legumes than forbs. These results do not correspond with the feeding trial. We suggest that the voles usually consume grasses in the field because grasses are abundant and readily available, but prefer protein-rich forbs when possible.     

Is feeding on mosses by groundhoppers in the genus <Emphasis Type="Italic">Tetrix</Emphasis> (Insecta: Orthoptera) opportunistic or selective?

Groundhoppers are considered to be detrito-bryophagous, and moss phyllodes represent a main food consumed by all studied species. We studied the food biology of two groundhoppers: the stenotopic habitat specialist Tetrix ceperoi (Bolivar, 1887) and the eurytopic T. tenuicornis (Sahlberg, 1893). These species occurred syntopically in an abandoned sand pit in the Czech Republic. The dietary preferences of the two species were very similar, with detritus being the dominant component, followed by mosses and other kinds of organic matter. The eurytopic T. tenuicornis consumed a greater diversity of mosses than the stenotopic T. ceperoi. The most frequently consumed mosses were the dominant species at the locality (Barbula spp., Bryum caespiticium, and Ceratodon purpureus), but some species-specific preferences were evident in the consumption of other moss species. To determine whether these groundhoppers mainly consumed mosses to obtain the water in their tissues, we compared the food composition at two sites that differed considerably in water availability. A selective consumption of mosses according to the water availability at the sites was evident. At the dry site, groundhoppers frequently consumed mosses that are simultaneously more tolerant to desiccation and nutritionally richer (species in the genera Barbula and Ceratodon) than the other mosses. Our results indicate that although groundhoppers generally consume those mosses that are most available, they do show some preference for mosses according to their nutritional quality and according to their ability to retain water under dry conditions.     

Nitrogen transfer between herbivores and their forage species

Herbivores may increase the productivity of forage plants; however, this depends on the return of nutrients from faeces to the forage plants. The aim of this study was to test if nitrogen (N) from faeces is available to forage plants and whether the return of nutrients differs between plant species using ¹⁵N natural abundance in faeces and plant tissue. To investigate the effect of grazing on N transfer, we carried out a grazing experiment in wet and mesic tundra on high Arctic Spitsbergen using barnacle geese (Branta leucopsis) as the model herbivore. N inputs (from faeces) increased with grazing pressure at both the wet and mesic sites, with the greatest N input from faeces at the wet site. The δ¹⁵N ratio in plant tissue from grazed plots was enriched in mosses and the dwarf shrub species, reflecting the δ¹⁵N signature of faeces-derived N, but no such pattern was observed in the dominant grasses. This study demonstrates that the δ¹⁵N signature of faeces and forage species is a useful tool to explore how grazing impacts on N acquisition. Our findings suggest that plant species which acquire their N close to the soil surface (e.g. mosses) access more of the N from faeces than species with deeper root systems (e.g. grasses) suggesting a transfer of N from the preferred forage species to the mosses and dwarf shrubs, which are less preferred by the geese. In conclusion, the moss layer appears to disrupt the nitrogen return from herbivores to their forage species.     

The effects of pollen consumption of transgenic Bt maize on the common swallowtail, Papilio machaon L. (Lepidoptera, Papilionidae)

Effects of exposure to maize pollen of event Bt176 (cultivar “Navares”) on the larvae of the European common swallowtail (Papilio machaon L.) were studied in the laboratory. First instar larvae were exposed to different pollen densities applied to leaf disks of Pastinaca sativa L. for 48 h. Pollen densities applied in this study were in the range recorded from the field. Larvae which were exposed to higher Bt maize pollen densities consumed more pollen and had a lower survival rate. The LD₅₀ with regard to larvae surviving to adulthood was 13.72 pollen grains consumed by first-instar larva. Uptake of Bt maize pollen led to a reduced plant consumption, to a lower body weight, and to a longer development time of larvae. Effects on pupal weight and duration of the pupal period were present but less pronounced and smaller than effects on larvae. Larvae having consumed Bt-maize pollen as first instars had a lower body weight as adult females and smaller forewings as adult males. We conclude that possible effects of Bt maize on European butterflies and moths must be evaluated more rigorously before Bt maize should be cultivated over large areas.     

Plastic changes in head size during juvenile development of the butterfly <Emphasis Type="Italic">Pieris napi</Emphasis>

Among herbivorous insects, the ability to change adaptive traits plastically in response to novel host plants is advantageous for coping with sudden environmental shifts. The host plants in our study were two closely related species, viz., Arabis flagellosa (tougher leaves, i.e., they are physically defended) and A. gemmifera (softer leaves that are physiologically defended). We demonstrated that young larvae of the butterfly Pieris napi are able to plastically change head size during development in response to changes in food plant species. When larvae were fed the physically defended A. flagellosa, the head sizes of third instar larvae emerging from eggs originally collected from leaves of both A. flagellosa and A. gemmifera became identically larger. When larvae fed on the physiologically defended A. gemmifera, the head sizes of third instar larvae emerging from eggs originally collected from leaves of both A. flagellosa and A. gemmifera became identically smaller. When leaves of A. flagellosa were presented to fourth instars reared on A. flagellosa, larvae with larger heads consumed more food than those with smaller heads. In contrast, when leaves of the physiologically defended A. gemmifera were presented to fourth instar larvae reared on A. gemmifera, larvae with smaller heads processed more food than those with larger heads. Hence, larvae of P. napi retain the capacity for adaptive plastic responses to novel host plant species.     

Comparative nutritional ecology of grass-feeding in a sub-Antarctic beetle: the impact of introduced species on Hydromedion sparsutum from South Georgia

South Georgia has many introduced plant and animal species, a consequence of its long history of human habitation. Introduced reindeer have a strong effect on the vegetation of the Stromness Bay area by causing the replacement of indigenous species by grazing-tolerant grasses such as the exotic Poa annua, and in certain circumstances, the indigenous Festuca contracta. Recently it has been argued that an introduced predatory carabid has contributed to declines in the abundance and an increase in the body size of adults of the indigenous perimylopid beetle Hydromedion sparsutum. However, it also appears that body size of these beetles is smaller in areas where exotic grasses predominate compared to undisturbed areas. Here we test the hypothesis that by causing the spread of poorer quality grasses, especially the exotic Poa annua, reindeer may be having an indirect effect on H. sparsutum. To do this we examined the nutritional ecology of H. sparsutum larvae on four grass species which form a major part of its diet, viz. the indigenous Parodiochloa flabellata, Phleum alpinum and Festuca contracta, and the exotic Poa annua. Larvae showed the highest growth rate on Parodiochloa flabellata, followed by Phleum alpinum, F. contracta and Poa annua. These differences are due to poorer absorption of the exotic grass, and poorer utilization of the absorbed material in the case of F. contracta. Poor growth of larvae on F. contracta appears to be due to its low water and nitrogen contents, whereas in the case of P. annua a combination of low water content and high nitrogen content may be responsible for low growth rates. Low growth rates associated with poor-quality food may lead either to a prolongation of the life cycle or of the length of feeding bouts of an insect. Neither option appears to be feasible for H. sparsutum, and this means that the outcome of feeding on poorer-quality foods would be a reduction in final adult size. This has fitness consequences for the beetle. Hence it appears that by causing the spread of grasses that are unsuitable for growth of H. sparsutum, reindeer may be having an indirect effect on this beetle species. Received: 18 August 1996 / Accepted: 7 February 1997     

Fruit‐ and seed‐feeding habit of the crane fly Libnotes puella (Diptera: Limoniidae) in Ryukyu Islands,Japan

Although most crane fly larvae consume decaying plant materials and their associated microorganisms, all Libnotes species investigated so far are known to be xylophilous insects. Here we report the novel herbivorous feeding ecology of Libnotes puella. We found that L. puella larvae consumed the fruits or seeds of three unrelated plants, Mitrastemon yamamotoi (Mitrastemonaceae), Balanophora tobiracola (Balanophoraceae) and Barringtonia racemosa (Lecythidaceae). The larvae live within dense tubes formed by their feces fastened by their mucous excretions at the final stage, and they pupate within such tubes. This is the first detailed documentation of the fruit‐ and seed‐feeding habit of crane flies.     

Feeding ecology of the hibernating primate Cheirogaleus medius: how does it get so fat?

The fat-tailed dwarf lemur (Cheirogaleus medius; Cheirogaleidae) lives in the tropical forests of Madagascar. It is exceptional among primates, because this small nocturnal lemur hibernates during the dry season from the end of April until October. This field study was carried out to assess seasonal changes in body mass and behavioral traits (locomotor activity, feeding ecology) of C. medius that enable this species to accumulate large quantities of fat within weeks. Feeding observations of 36 radio-collared individuals were combined with a mark-recapture study in western Madagascar during the rainy seasons from 1995 to 1998. Pulp of fruit species not consumed, as well as fruit species eaten by C. medius was analyzed for lipid and sugar contents. Body mass changes of recaptured individuals revealed that C. medius may double its body mass within a few weeks. Most of the increase in body mass took place between March and April after infants had been weaned and directly before the onset of hibernation. Locomotor activity was significantly reduced during the period of body mass gain. During the entire study, fruits, nectar, and flowers of 34 different plant species comprised about 80% of the diet, supplemented by a seasonally varying intake of animal prey. Lipid contents of consumed fruits were comparatively low throughout the study period. No difference in lipid content was detectable between fruit species consumed and not consumed by C. medius. During prehibernation fattening, C. medius consumed mostly fruit species with a high sugar content, significantly higher than that of fruit species that were not consumed. The results suggest that a reduction in locomotor activity as well as a preference for fruit species with a high sugar content enable C. medius to deposit large quantities of fat in a few weeks. Received: 15 March 1999 / Accepted: 30 June 1999     

Diet and Geophagy Across a Western Amazonian Parrot Assemblage

We identified species‐ and community‐level dietary characteristics for a species‐rich Amazonian parrot assemblage to determine relationships among dietary metrics and use of geophagy sites. Previous studies suggest that soil is consumed at geophagy sites in this region mainly to supplement dietary sodium. We accumulated 1400 feeding records for 16 parrot species over 2 yr and found that seeds, flowers, and fruit pulp featured prominently in diets, while bark, insects, and lichen were consumed in small quantities. Food availability across 1819 trees was measured, and we found that flower availability was highest in the dry season and fruit production peaked in the wet season, but that phenology patterns of the 20 most commonly foraged plant species suggest no serious food bottlenecks. Partitioning of available food resources among the 13 most commonly encountered parrots is suggested by an ordination analysis (DCA), which placed the large macaws (Ara) with the Amazona parrots at the ‘primary forest’ end of a dietary resource axis and four smaller species at the ‘successional forest’ end of the axis. Parrot species associated with successional forest also consumed less plant species overall. Furthermore, these parrot species consuming successional forest resources had higher claylick visitation rates than those consuming primary forest resources suggesting they derive the greatest benefits from soil consumption.     

Poleward increase in feeding efficiency of leafminer Stigmella lapponica (Lepidoptera: Nepticulidae) in a latitudinal gradient crossing a boreal forest zone

Damage to plant communities imposed by insect herbivores generally decreases from low to high latitudes. This decrease is routinely attributed to declines in herbivore abundance and/or diversity, whereas latitudinal changes in per capita food consumption remain virtually unknown. Here, we tested the hypothesis that the lifetime food consumption by a herbivore individual decreases from low to high latitudes due to a temperature-driven decrease in metabolic expenses. From 2016 to 2019, we explored latitudinal changes in multiple characteristics of linear (gallery) mines made by larvae of the pygmy moth, Stigmella lapponica, in leaves of downy birch, Betula pubescens. The mined leaves were larger than intact leaves at the southern end of our latitudinal gradient (at 60°N) but smaller than intact leaves at its northern end (at 69°N), suggesting that female oviposition preference changes with latitude. No latitudinal changes were observed in larval size, mine length or area, and in per capita food consumption, but the larval feeding efficiency (quantified as the ratio between larval size and mine size) increased with latitude. Consequently, S. lapponica larvae consumed less foliar biomass at higher latitudes than at lower latitudes to reach the same size. Based on space-for-time substitution, we suggest that climate warming will increase metabolic expenses of insect herbivores with uncertain consequences for plant–herbivore interactions.     

Food consumption in Gerris (Hemiptera)

Summary The parameters influencing food consumption in larvae and adults of five species of Gerris were studied. An experimental components analysis was utilized with emphasis placed on measurements of the length of time the insects spent handling food items, and the amount of food in the gut at any one time. The following characteristics were noted: (1) The maximum feeding time required to achieve satiation was 2–2.5 h for all gerrids above 10 mg wet weight. For gerrids below this weight, feeding time declined at a logarithmic rate. (2) Body size had little influence on the duration of the feeding period after food deprivation; only with the first and second instar larvae was a significant difference noted. (3) The average duration of the feeding and non-feeding periods was 10.4 and 24.6 min respectively for satiated adult G. remigis in the presence of excess food. (4) Signifcant differences in relative digestive rate existed between adult and larvae irrespective of species. (5) The smaller the gerrid, the greater the volume relative to its body weight that could be consumed at a single feeding, and for all gerrids, the amount consumed per day was greater than the maximum amount that can be ingested at a single feeding, this difference being larger in the larvae than in the adults. (6) The relationship between daily amount consumed and temperature was linear for four species, increasing with increasing temperature; food consumption in G. remigis, however, peaked at about 19°C, and declined linearily at temperatures both above and below this value. (7) Irrespective of instar and stadium duration, food consumption for G. notabilis peaked within a stadium about 40% of the way through the stadium.