Functional response of suspension feeding anuran larvae to different particle sizes at low concentrations (Amphibia)

The influence of particle size, initial particle concentration and larval stage on the ingestion rate, ‘retention efficiency’, and filtering rate of anuran larvae with varying filter apparatus anatomy and different life histories was investigated for four species. Larvae of premetamorphic Stages 28 and 32 and prometamorphic Stage 40 were selected for filtering experiments on the basis of their different growth rates. Three different sizes of silica gel particles were offered as mock food. Particle concentration was measured photometrically. The Michaelis-Menten model was used to describe the dependency of ingestion rate, filtering rate, and ‘retention efficiency’ upon initial particle concentration, and to calculate maximum ingestion rate, threshold concentration, and the half-saturation constant. (1) The highest ingestion rates, filtering rates and ‘retention efficiencies’ were achieved by Xenopus laevis larvae, followed by Bufo calamita larvae. Bufo bufo larvae lay at the opposite end of the scale. Rana temporaria larvae were placed between B. calamita and B. bufo larvae. This order is attributed to differences in life histories, especially the different breeding environments in which these larvae occur. (2) The larger the particle size and the older the stage, the greater the tendency toward saturation of the ingestion rate, filtering rate and ‘retention efficiency’. These filtration parameters are graded according to particle size. The ingestion rate (number of particles), filtration rate and ‘retention efficiency’ are greatest for PS3. Ingestion volume is greatest for PS 1. The difference between PS3 and PS2 on the one hand, and PS1 on the other, is often great; for Stage 28 X. laevis it is very great. This shows that larvae ingest large particles more effectively, and that the most effective ingestion takes place at Stages 28 and 32, owing to the growth function of these stages. The ability of larvae to ingest large particles effectively is possibly a very basic phylogenetic characteristic. (3) The threshold concentration is lowest when the particles are at their largest. In accordance with conclusions drawn by other authors, threshold feeding is attributed to regulation by buccal pumping and mucus production. Considerable importance is attributed to threshold feeding with respect to larval adaptation to oligotrophic environments.     

Pathophysiological influences of the Heterorhabditis bacteriophora complex on fifth-instar larvae of the red humped caterpillar, Schizura concinna: Changes in feeding rate,larval weight,and frass production

At 28.5°C, oral dosages of the invasive juveniles of Heterorhabditis bacteriophora and intrahemocoelic injections of its associated bacterium, Xenorhabdus luminescens, resulted in a decrease in larval feeding rate, larval wet weight, and frass production in its host, the seventh-instar larvae of Schizura concinna.     

Mosquito fauna inhabiting water bodies in the urban environment of Córdoba city,Argentina, following a St. Louis encephalitis outbreak

An understanding of urban aquatic environments as mosquito larval habitats is necessary to prioritize sites for surveillance and control of arbovirus vectors in urban areas. Natural and artificial water bodies at ground level that may be larval mosquito habitats in Córdoba city, Argentina were surveyed. Data on the characteristics of aquatic sites and the presence and abundance of mosquito larvae and pupae were collected in the summer of 2006, coinciding with the first report of human WNV and following an outbreak of St. Louis encephalitis in 2005. Eight species in the genera Aedes, Culex, and Mansonia were identified. At 64.2% (34 of 53) of the sites, only one species was collected, while 3.8% (2 of 53) had three associated species, the highest richness found per site. Culex quinquefasciatus represented over 99% (out of 32,729) of the specimens. It was also the most widely distributed and detected under diverse habitat conditions. Although puddles and semi‐permanent pools harbored a greater number of species, drainages and channels may be more relevant as risk factors from an epidemiological point of view because they showed the highest larval densities, mainly of Cx. quinquefasciatus (vector of SLE and WNV). Also, higher densities of this species were associated with stormwater runoff and sewage water, thus water management systems should be targeted and closely monitored for mosquito control purposes.     

Host plant utilization by butterfly larvae in the Andaman and Nicobar Islands (Indian Ocean)

The larval food plants of the butterflies of the Andaman and Nicobar islands have not been studied, although the butterfly fauna per se is fairly well known. For the first time we report the food plants of the larvae of 120 species of butterflies from these islands on the basis of laboratory rearing and field studies. This information is essential for the formulation of management programmes for butterfly conservation on these islands which are known to harbour critical swallowtail and (possibly) danaine faunas.     

水生昆虫幼虫取食行为研究进展

作为生存的重要行为,水生昆虫幼虫的取食是水生昆虫行为学研究的重点.本文综述了水生昆虫幼虫的取食习性、取食机理、取食行为、消化过程和取食影响因素等方面的研究进展,指出了今后应深入研究水生昆虫取食机理,以促进水生昆虫行为学研究,进一步为人工繁育水生资源昆虫提供理论支持.     

Activity and swimming speed at time of first feeding of halibut (Hippoglossus hippoglossus) larvae

Atlantic halibut larvae show an increase in activity, together with a decrease in swimming speed during active periods, occurring from day 26 onwards, which corresponds approximately to 50% yolk absorption.     

Adaptive visually‐mediated movements of Littorina irrorata (Mollusca: Gastropoda) when displaced from their natural habitat

Littorina irrorata displaced from their natural location amid plant stems in the upper inter‐tidal zone to areas of intertidal zone devoid of vegetation, oriented onshore under all sky and light conditions tested. The responses of snails tested in experimental arenas in the upper intertidal zone indicated that the natural substrate slope of 3 degrees was ignored in favor of movement toward a black paper rectangle. Subsequent releases on natural substrate supported the conclusion that the onshore‐oriented response resulted from visual perception of a dark area (bushes and trees near the high tide line). Where vegetation was equally tall in all directions, snails oriented toward the closest vegetation regardless of the actual onshore direction.     

A duration constant for worker-to-larva trophallaxis in fire ants

Summary The allocation of liquid food by workers to larvae, a central process in ant biology, could be regulated by the frequency of trophallaxis, its duration, or both. In 4th-instar fire ant larvae, the duration of trophallaxis, bolus size, and the rate at which boluses were swallowed were all constant, indicating that the volume of food ingested during each worker-larva trophallaxis was both small and constant. Neither larval size over a 20-fold volume range nor larval starvation had a significant effect on duration of trophallaxis (mean = 11s, SD = 2s), bolus swallowing rate (mean = 2/s, SD = 0.5/s), or bolus volume (mean = 0.0675 nl, SD = 0.0002 nl, based on the assumption that the stomodaeum's epithelial layer is not expandable). Larval body orientation and larval location within the brood pile also had no effect on duration. Durations of trophallaxis by workers of different sizes were similar. Durations of trophallaxis for 1st-, 2nd-, and 3rd-instar worker larvae were also constant but greater than that for 4th-instar worker larvae. Fourth-instar minim larvae (from founding colonies) and 4th-instar worker larvae (from mature colonies) were fed for the same duration by workers but for different durations by founding queens. Founding queens fed minim larvae longer than they fed worker larvae. The durations of feedings to 4th-instar sexual larvae were more variable than those to worker larvae. Altogether, these findings indicated that 4th-instar worker larvae ingested a small, nearly constant volume of food (mean = 1.50 nl, SD = 0.005 nl) during each trophallactic event. Consequently, the long-term allocation of liquid food by workers to these larvae is regulated by the frequency of trophallaxis. Several other ant species showed a similar brevity and constancy in the duration of worker-larva trophallaxis. This brevity of worker-larva trophallaxis is in contrast to the duration of worker-worker trophallaxis.Although the duration of worker-larva trophallaxis appears to be determined by the worker, the data are not totally consistent with this interpretation.     

Diel abundance, migration and feeding of fish larvae (Eleotridae) in a floodplain billabong

Eleotrid larvae (2.1–16 mm) were collected from surface waters of a billabong in south-eastern Australia. Estimates of larval density in plankton net samples at night averaged 148.3 larvae per m³ and 16.6 larvae per m³ during the day. In contrast, pump samples provided density estimates of 8.3 larvae per m³ at night and 0.9 larvae per m³ during the day. Larval densities did not differ between open water, snag (fallen tree) and Typha habitats, but Typha habitats yielded larger larvae than other habitats. 32.9% of larvae in pump samples were damaged and unmeasurable, creating a bias favouring larger larvae. The modal length of larvae in net samples at night was 5–6 mm, compared with 3–4 mm during the day, reflecting both greater net avoidance by larger larvae during the daytime and dispersal of smaller larvae from the surface at night. Dispersion patterns of larvae suggest that classes of larvae smaller than, and larger than 5.0 mm exhibit reciprocal diel vertical migration behaviour linked to ontogenetic changes in diet. Larvae less than 5 mm fed only during the day and preyed exclusively on rotifers, whereas larger larvae continued to feed at night and consumed mostly planktonic crustaceans.     

Effects of the availability of food and water on reproduction in the African army worm, Spodoptera exempta

ABSTRACT. Female Spodoptera exempta (Walker) (Lepidoptera: Noctuidae) moths require access to water to achieve hydration and maturation of their oocytes if they are to achieve their potential fecundity. For moths provided with water, the main factor limiting fecundity is moth weight. There is some evidence that sucrose in the adult diet can increase fecundity, particularly in lighter moths from a suboptimal larval feeding regime. Moths fed sucrose live longer, but complete oviposition at about the same age as moths provided only with water. Dietary protein and amino acids have no effect on fecundity or longevity. Although- multiple matings are frequent in the laboratory, female S.exempta only need to mate once to complete oviposition. Differences are apparent in the relative contribution of larval and adult feeding to reproduction in Noctuidae. Some species, like S.exempta , require only water to achieve their reproductive potential, while others (e.g. Heliothis spp.) are dependent on sugars in the adult diet. Female S.exempta denied access to water or food until night 3 after eclosion and then provided with water or sucrose, commence oviposition on night 4 and have fecundities comparable with those moths fed from emergence.     

Effects of salinity on larval and early juvenile growth of an extremely euryhaline crab species,Armases miersii (Decapoda: Grapsidae)

The neotropical crab Armases miersii (Rathbun, 1897) breeds in supratidal rock pools, where great salinity variations occur. In laboratory experiments, all larval stages and the first juveniles were reared at six different salinities (5–55 PSU, intervals of 10 PSU). In five series of experiments, exposure to these conditions began either from hatching (Zoea I) or from the onset of successively later stages (Zoea II, III, Megalopa, Crab I). Growth was measured in terms of dry weight, carbon, nitrogen and hydrogen content. At osmotically extreme conditions (5 and 55 PSU, resp.), all stages showed minimum biomass accumulation; this was consistent with maximum mortality and longest duration of development (data presented in a separate paper). Successively later exposure to these salinities tended to reduce these effects. Lowest mortality and shortest time of development occurred generally at 15–25 PSU, indicating an optimum at moderately reduced salinities. This response pattern, however, was not congruent with that observed in growth. Biomass accumulation was initially maximum within a wide range of salinities (15–45 PSU), but in the Zoea II and III stages, this range tended to narrow and to shift towards higher salinities (35–45 PSU). These trends reversed in the Megalopa and Crab I, where maximum growth occurred again in a wider range and at lower salinities (15–35 PSU). The reduction of zoeal growth in moderately dilute media (15–25 PSU), which were optimal for survival and development, is interpreted as an energetic cost of hyper-osmoregulation, which begins already at hatching. Five PSU caused hypo-osmotic stress, exceeding in the long term the larval capacity for hyper-regulation. Poor zoeal survival and growth at 55 PSU are interpreted as effects of hyper-osmotic stress. In the Megalopa and Crab I, reduced growth at salinities 35 PSU may reflect the energetic costs of hypo-osmoreguation beginning in these stages. Our data suggest that the physiological adaptations of larval and early juvenile A. miersii allowing for survival and development in a physically harsh and unpredictable habitat imply a trade-off with reduced growth, due to energetic costs of osmoregulation.     

Is the expression of autogeny by Culex molestus Forskal (Diptera: Culicidae) influenced by larval nutrition or by adult mating,sugar feeding,or blood feeding?

Culex molestus Forskal is suspected to have been introduced into southern Australia during the 1940s. Investigations to determine factors influencing the expression of autogeny, the response of this mosquito to potential blood meals, and the subsequent influence on oviposition were undertaken. Immature mosquitoes raised at five feeding regimes had mortality rates, development rates, wing length, and autogenous egg raft size measured. All surviving female mosquitoes laid autogenous eggs but there was a significant difference between the mean number of eggs per raft. For mosquitoes raised at each of the feeding regimes, there was a significant linear relationship between the number of eggs per autogenous egg raft and wing length. Newly emerged mosquitoes were offered a blood meal (i.e., rodent) daily but no blood feeding occurred until the autogenous egg raft was laid. There was no statistical difference in the rate of autogenous oviposition or post-oviposition blood feeding between control or treatment groups. The results of this study indicate that Cx. molestus is perfectly adapted to subterranean habitats in close association with human habitation, but their preference to delay blood feeding until up to day 8 following emergence may reduce their relative importance as a vector of arboviruses.     

The effect ofMetarhizium anisopliae (DAT F-001) concentration and exposure time on the survival of the subterranean pasture pest,Adoryphorus couloni (Col.: Scarabaeidae)

The virulence of the DAT F-001 isolate ofMetarhizium anisopliae forAdoryphorus couloni was tested by exposing final instar larvae (L3) to concentrations of 10¹ to 10⁷ spores/g in a sand-peat mix for up to 112 days at 20°±2°C. All concentrations were pathogenic to L3 larvae and survival was dependent on concentration and correlated with exposure time. The time to kill 50% of the treated larvae (LT₅₀) ranged from 18.9 days (10⁷ spores/g) to 82.7 days (10¹ spores/g). The effect of DAT F-001 on feeding by L3 larvae was determined by comparing the production and weight of frass pellets/larva/day of untreated control larvae with larvae rolled in sporulating cultures ofM. anisopliae DAT F-001 and DAT F-054 (low virulence). Exposure to, and infection byM. anisopliae DAT F-001 had minimal impact on larval feeding. L3 larvae continued to feed at the same rate as both untreated and DAT F-054 treated larvae virtually until they died.

---

Résumé La virulence deM. anisopliae DAT F-001 pourA. couloni a été analysée en exposant des larves L3 à des concentrations de 10¹ à 10⁷ spores/g dans un mélange de sable et de tourbe pendant un maximum de 112 jours à une température de 20°±2°C. Toutes les concentrations sont pathogènes pour les larves L3; la survie dépendait de la concentration et est en corrélation avec le temps d'exposition. Les LT₅₀ sont compris entre 18,9 jours (10⁷ spores/g) et 82,7 jours (10¹ spores/g). L'effet de DAT F-001 sur l'alimentation des larves L3 a été évalué en comparant la production et le poids des fèces/larve/jour des larves non-traitées avec des larves roulées dans des cultures sporulées deM. anisopliae DAT F-001 et DAT F-054 (faible virulence). L'exposition àM. anisopliae DAT F-001 suivie de l'infection a peu d'effet sur l'alimentation des larves. Les larves L3 continuent à s'alimenter au même rythme que les larves non-traitées de DAT F-054, quasiment jusqu'à leur mort.

     

Size of prey ingested by whitefish,Coregonus sp., larvae. Are Coregonus larvae gape-limited predators?

The feeding ecology of whitefish, Coregonus , larvae in oligotrophic Lake Sarnen and eutrophic Lake Hallwil is presented, taking into consideration the size of the prey ingested in relation to the mouth size of larvae and to the availability of zooplankton.
When larvae grow from 10 to 16 mm their mouth width increases from 500 to 1000 μm while their gape height, with the mouth open at 45 and 90°, increases from 200 to 400 μm and from 400 to 700 μm, respectively, whichever lake is considered.
The differences found in the mean prey width between the two lakes arise in part from the composition of diets, and in part from differences in size of the available prey organisms. Whatever the origin of the larvae and the taxon we consider, larvae seem to ingest the most abundant prey size without selecting the biggest ones available even if, from a mechanical point of view, they would be able to ingest them.
Taking into account the generally low density of zooplankton in the uppermost layer of the lake, we conclude that whitefish larvae eat in the manner such as to decrease the cost of prey capture, in terms of energy and time, by choosing the more abundant prey available.     

不同投料方式对黑水虻幼虫生长性能的影响

以获得黑水虻Hermetia illucens转化有机废弃物的养殖投喂工艺参数为目标,采用实验室小试模拟试验,以餐厨垃圾为试验原料,研究不同投料方式(1次、2次、3次和4次投料)对黑水虻转化餐厨垃圾过程中幼虫生长性能的影响。结果表明,采用多次投料方式,随着投料次数增加,对转化物料料温波动影响较大,不利于幼虫快速生长;在投虫量和投料量相同条件下,养殖周期为10 d,其中以1次投料处理组的收虫体重、体长、单位面积虫产量为最高,料虫比为最低,与2次投料差异不显著(P>0.05),但与3次、4次投料处理组差异显著(P<0.05);黑水虻转化废弃物前期较低的物料含水率更加有利于虫体生长,而后期物料含水率较高则更为有利。通过生产性能分析发现,从投料回报效果角度考虑生产性能以1次投料为最佳,而从高效率处理餐厨垃圾和投料回报效果两者角度综合分析,生产性能以2次投料为最佳。该结果可为构建黑水虻转化餐厨垃圾标准化生产工艺参数技术体系奠定基础。