Effect of food concentration on growth, reproduction and survivorship of Bosmina longirostris (Cladocera)

SUMMARY. 1. Body growth, reproduction and survivorship of Bosmina longirostris were monitored at four food concentrations (0.05, 0.10, 0,25 and 2.50 ing Cl⁻¹) to examine the extent to which food concentration affects these life-history parameters.
2. Food concentration had a significant effect on growth, and most of the reproductive parameters (size and age at maturation, brood size, instar duration and egg development time). More than 60% of animals died before maturation at the lowest food concentration, although most animals survived until maturation at other food concentrations.
3. Change in life-history parameters resulted in a decrease in rate of population growth ( r ) from 0.310 to 0.020 day⁻¹ with decreasing food concentration, showing that this cladoceran is highly food-limited in many lakes.
4. Importance of the effect of food concentration on egg development time was emphasized in relation to analysis of natural populations.     

Phenotypic plasticity and constancy of life-history traits in laboratory clones of Daphnia magna Straus: effects of neonatal length

1. The phenotypic constancy of four laboratory Daphnia magna clones in fitness-related life-history traits, such as age and clutch size at maturity, was studied among consecutive experimental runs in differing food environments.
2. A significant part of the observed clonal and genetic-by-environmental variation in age and clutch size at maturity was explained by experimentally uncontrollable variations in neonatal body length.
3. Despite food availability, neonatal length determined the number of instars invested to maturity and thus maturation age. Clonal differences in neonatal length and thus in maturation instar occurrence across environments explained most of the clonal variability observed in maturation age.
4. Although interclonal differences in clutch size existed, most of the phenotypic plasticity observed for clutch size was mediated by clonal differences in neonatal length.
5. Clonal differences in neonatal length and in the occurrence of maturation instars across environments dramatically affected the body length of instar IM-2 where provisioning of eggs take place. Since clutch size is determined from clutch mass and clutch mass was strongly related to the body length of instar IM-2, clonal differences across environments in body length of instar IM-2 mirrored clonal differences across environments in clutch size.
6. The results reported in the present study show that maternally mediated traits such as neonatal length affect how genotypes respond to different environmental selection regimes (genetic-by-environmental interaction). Future research needs to focus on the effects of neonatal length on the heritability or genetic variation of the reaction norms, since prediction of the response to selection is a key research objective in quantitative genetic studies.     

Phenotypic plasticity in Daphnia magna Straus: variable maturation instar as an adaptive response to predation pressure

Life history responses of four Daphnia magna clones at two food levels were studied to assess the importance of maturation instar on the plasticity of fitness responses under simulated mortality regimes. Females of the clones studied could vary offspring size with consequent effects on their maturation time. Significant genetic variability in life history and fitness responses, measured as the intrinsic rate of population increase, within and across food levels was observed, but most of this variation could be attributed to maturation instar differences among clones within and across environments. In the laboratory, without extrinsic mortality, females maturing earlier always had higher fitness than those maturing later, indicating a clear fitness cost of delaying maturity. Nevertheless using a model, we showed that the observed maturation instar effects on life history responses can lead to differences in fitness under different size-selective predation regimes, such that females with delayed maturity have higher fitness under invertebrate predation while females maturing earlier have higher fitness under fish predation regimes. These results suggest that intraclonal variation in offspring size and hence in the number of maturation instars can be an adaptation to living in habitats subject to temporal fluctuations in fish and invertebrate predation pressure.     

The effects of dictyostelids on the formation and maturation of myxomycete plasmodia

Dictyostelids (cellular slime molds) and myxomycetes (plasmodial slime molds) are two groups of mycetozoans usually present and often abundant in the soil and litter microhabitats of terrestrial ecosystems. Because they utilize the same food resource and occur together in a spatially limited and clearly defined microhabitat, the potential for ecological interactions would seem to exist. However, relatively few previous studies have considered this aspect of mycetozoan ecology. In the present study twenty-eight isolates (8 species) of dictyostelids were co-cultured in all possible pair-wise combinations with fourteen isolates (7 species) of myxomycetes to determine if there were any effects on the production of fruiting bodies. Dictyostelids showed little or no delay in culmination and only random and inconsistent reductions in sorocarp abundance when co-cultured with myxomycetes. In contrast, myxomycetes displayed a number of specific effects. The heterothallic isolates exhibited delays in plasmodial formation and/or maturation, with some pairings showing little to no effect, while others displayed nearly complete inhibition of plasmodial formation or maturation. Apomictic isolates, in general, were much less affected, with only a few combinations displaying significant delays in both formation and maturation of plasmodia.     

Temperature induces trade-offs between development and starvation resistance in Aedes aegypti (L.) larvae

Heightened temperature increases the development rate of mosquitoes. However, in Aedes aegypti (Diptera: Culicidae), the larvae of which commonly experience limited access to food in urban habitats, temperature effects on adult production may also be influenced by changes in the capacity of larvae to survive without food. We carried out experiments to investigate the effects of temperatures increasing at intervals of 2 °C from 20 °C to 30 °C on the growth, maturation rate and longevity of optimally fed larvae placed in starvation. Overall, both growth rate and starvation resistance were lower in the first three larval instars (L1-L3) compared with L4, in which growth of >75% occurred. Although increasing the temperature reduced the duration of each instar, it had a U-shaped impact in terms of the effect of initial growth on starvation resistance, which increased from L1 to L2 at 20 °C and 30 °C, remained constant at 22 °C and 28 °C, and decreased at 24 °C and 26 °C. Growth from L2 to L3 significantly increased starvation resistance only from 26 °C to 30 °C. Increased temperature (>22 °C) consistently reduced starvation resistance in L1. In L2-L4, increments of 2 °C decreased starvation resistance between 20 °C and 24 °C, but had weaker and instar-specific effects at >24 °C. These data show that starvation resistance in Ae. aegypti depends on both instar and temperature, indicating a trade-off between increased development rate and reduced starvation survival of early-instar larvae, particularly in the lower and middle temperatures of the dengue-endemic range of 20-30 °C. We suggest that anabolic and catabolic processes in larvae have distinct temperature dependencies, which may ultimately cause temperature to modify the density regulation of Ae. aegypti populations.     

Relation of feeding,growth, and metabolism to age in the larval,female house cricket

The maximum growth rate occurs in the first half of the 7th and 8th larval instars of the house cricket, at which time food and water consumption is maximal. Growth ceases in the last 2 to 3 days of each instar when food consumption is almost nil. The metabolic rate is twice, and the locomotory activity is four times, higher in the first 2 to 3 days than in the last 2 to 3 days of each instar. The %-gain in dry wt is 120% for the 7th and 139% for the 8th instar. The average digestive coefficient (AD) for the 8th instar is 67% and the average efficiency of food conversion to tissue (dry wt ECI) is 27%. The average daily food consumption for 8th instar larvae is 31.4 mg, and, therefore, we calculate that an average of 12 mg food is burnt per day for energy which is confirmed by the observed average V_O2 of 1.2 ml O₂/g-cricket/hr. Total lipids as %-total wt (239% mg-gain) increases in the first 4 days then remains constant in spite of cessation of feeding in the last 2 days. The RQ confirms the conversion of carbohydrates to lipids in the first half of each instar. In the moulting cycle carbohydrates are used for maintenance (when not feeding), but lipids are used at apolysis.     

丛枝菌根真菌定殖银中杨对舞毒蛾幼虫食物利用及适应性的影响

丛枝菌根真菌可提高寄主植物的抗虫性,但在林木方面的研究较少。为探明丛枝菌根真菌对林木的抗虫机制,以银中杨Populus alba × P. berolinensis为研究对象,分别进行摩西斗管囊霉Funneliformis mosseae (FM)、根内根孢囊霉Rhizophagus intraradices (RI)接种处理,以不接种处理为对照,比较两种丛枝菌根真菌定殖银中杨对舞毒蛾Lymantria dispar幼虫食物利用及适应性的影响。结果显示,FM处理可显著降低(P<0.05) 3-5龄幼虫的取食量、食物转化率和3-4龄幼虫食物利用率,且显著抑制(P<0.05) 4龄幼虫酸性磷酸酶(ACP)、羧酸酯酶(CarE)和谷胱甘肽S-转移酶(GSTs)活性及5龄幼虫淀粉酶、脂肪酶、胰蛋白酶和ACP活性。而RI处理可显著降低(P<0.05) 3-5龄幼虫的食物消耗率,显著抑制(P<0.05) 4龄幼虫CarE、GSTs和超氧化物歧化酶(SOD)活性及5龄幼虫ACP、GSTs和SOD活性。结论认为,FM和RI定殖均能在一定程度上诱导银中杨产生抗虫性,但综合来看FM比RI定殖银中杨产生的抗虫性更强。     

Tissue Damage Disrupts Developmental Progression and Ecdysteroid Biosynthesis in Drosophila

In humans, chronic inflammation, severe injury, infection and disease can result in changes in steroid hormone titers and delayed onset of puberty; however the pathway by which this occurs remains largely unknown. Similarly, in insects injury to specific tissues can result in a global developmental delay (e.g. prolonged larval/pupal stages) often associated with decreased levels of ecdysone – a steroid hormone that regulates developmental transitions in insects. We use Drosophila melanogaster as a model to examine the pathway by which tissue injury disrupts developmental progression. Imaginal disc damage inflicted early in larval development triggers developmental delays while the effects are minimized in older larvae. We find that the switch in injury response (e.g. delay/no delay) is coincident with the mid-3rd instar transition – a developmental time-point that is characterized by widespread changes in gene expression and marks the initial steps of metamorphosis. Finally, we show that developmental delays induced by tissue damage are associated with decreased expression of genes involved in ecdysteroid synthesis and signaling.     

Effects of food nutritive quality and Bacillus thuringiensis onfeeding behaviour, food utilization and larval growth of spruce budworm Choristoneura fumiferana (Clem.) when exposed as fourth- and sixth-instar larvae

Abstract 1 Feeding behaviours, and lethal and sublethal (growth, development and food utilization) effects of Foray 48B, a commercial formulation of Bacillus thuringiensis (kurstaki), were investigated on fourth‐ and sixth‐instar spruce budworm larvae according to food nutritive quality. Nitrogen and soluble sugar content of artificial diets were modified to obtain three different qualities of food, simulating variations in nutritive quality of host tree. 2 Larval development times were longer for Bt‐treated larvae and pupal weights were reduced for sixth‐instar larvae only. Bt‐induced mortality levels were influenced by food quality. Ingested dose of Bt and feeding inhibition times were strongly affected by the Bt treatment, but food quality affected only fourth‐instar larvae. Except for food digestibility, nutritional indices were negatively affected by the Bt treatment and by the reduction in food quality. 3 Contrary to early treated larvae (fourth instar), larvae treated at the beginning of the sixth instar were not able to compensate for Bt injury and were consequently more affected by the Bt‐treatment both in terms of lethal and sublethal effects. 4 Bt efficacy was not directly related to the ingested dose. 5 Increase in larval vulnerability to Bt was more likely a consequence of a general stress induced by a less suitable food than a direct interaction between Bt and food nitrogen or sugar compounds. 6 The application of Bt on late‐instar larvae could be a successful operational strategy at low population levels when field sprays target the insect instead of foliage protection.     

Food availability controls the onset of metamorphosis in the dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae)

In nature, larvae of the dung beetle Onthophagus taurus (Schreber 1759) are confronted with significant variation in the availability of food without the option of locating new resources. Here we explore how variation in feeding conditions during the final larval instar affects larval growth and the timing of pupation. We found that larvae respond to food deprivation with a reduction in the length of the instar and premature pupation, leading to the early eclosion of a small adult. To achieve pupation, larvae required access to food for at least the first 5 days of the final instar (= 30% of mean third‐instar duration in control individuals), and had to exceed a weight of 0.08 g (= 58% of mean peak weight in control individuals). Larvae that were allowed to feed longer exhibited higher pupation success, but increased larval weight at the time of food deprivation did not result in increased pupation success except for larvae weighing > 0.14 g. Larvae responded to food deprivation by initiating and undergoing the same sequence of developmental events, requiring the same amount of time, as ad libitum‐fed larvae once those had reached their natural peak weight. Our results reveal a striking degree of flexibility in the dynamics and timing of larval development in O. taurus. They also suggest that premature exhaustion of a larva's food supply can serve as a cue for the initiation of metamorphosis. Premature metamorphosis in response to food deprivation has been documented in amphibians, but this is, to the best of our knowledge, the first time such a behaviour has been documented for a holometabolous insect. We discuss our findings in the context of the natural history and behavioural ecology of onthophagine beetles.     

Effect of sublethal concentration of Bacillus thuringiensis var. kurstaki on food and developmental needs of the american bollworm, Helicoverpa armigera (Hübner)

Effect of sublethal concentration of B. thuringiensis on the first, third, fourth and fifth instar larvae of the American bollworm, H. armigera was investigated to study their response to food consumption, digestion, utilization, and their development till adult formation. The young larvae surviving B. thuringiensis treatment in their first instar and third instar delayed larval period by two to three days, but did not consume more food as compared to control. However, they showed higher digestibility of food as compared to control, which was compensated by their reduced ability to utilize the digested food for body substance. Contrary to the effect on first and third instar larvae, the fifth instar larvae surviving B. thuringiensis treatment in its fourth instar consumed less food, showed less absorption efficiency in digesting food, but compensated by increase in the utilization of ingested and digested food into body substance. Insects surviving B. thuringiensis HD-1 sublethal toxicity adapted to normal larval growth when fed on untreated food, depending upon insect growth prior to treatment. The moths emerging from B.thuringiensis treated larvae had sex ratio favouring females, and adult pairs laid less fertile eggs than those from the untreated ones. The response of B. thuringiensis treated larvae to their food and developmental needs is discussed.     

Larval ethanol exposure alters adult circadian free-running locomotor activity rhythm in Drosophila melanogaster

Alcohol consumption causes disruptions in a variety of daily rhythms, including the sleep-wake cycle. Few studies have explored the effect of alcohol exposure only during developmental stages preceding maturation of the adult circadian clock, and none have examined the effects of alcohol on clock function in Drosophila. This study investigates developmental and behavioral correlates between larval ethanol exposure and the adult circadian clock in Drosophila melanogaster, a well-established model for studying circadian rhythms and effects of ethanol exposure. We reared Drosophila larvae on 0%, 10%, or 20% ethanol-supplemented food and assessed effects upon eclosion and the free-running period of the circadian rhythm of locomotor activity. We observed a dose-dependent effect of ethanol on period, with higher doses resulting in shorter periods. We also identified the third larval instar stage as a critical time for the developmental effects of 10% ethanol on circadian period. These results demonstrate that developmental ethanol exposure causes sustainable shortening of the adult free-running period in Drosophila melanogaster, even after adult exposure to ethanol is terminated, and suggests that the third instar is a sensitive time for this effect.     

Inter- and intra-instar food consumption in the German cockroach, Blattella germanica

Food consumption was measured in an insecticide-susceptible (Orlando) and-resistant (Village Green) strain of German cockroach, Blattella germanica (Dictyoptera: Blattellidae), throughout each stadium. All instars exhibited a similar pattern of consumption over the course of the instar; consumption was low to moderate at the beginning of each instar, climbed steadily to a maximum near the middle, declined progressively from the mid-instar maximum, and ceased or was minimal several days before the next molt. Consumption ceased or was minimal during the final two to four days of each instar. Cumulative consumption for the six instars was significantly greater in the Village Green strain as compared with the Orlando strain. Village Green nymphs consumed 79.6±0.7 mg of rat chow while Orlando nymphs consumed 63.7±3.4 mg. Total consumption by instar increased significantly with each successive instar in the Village Green strain. In addition, Village Green sixth instar females consumed significantly more food than sixth instar males. A similar trend was observed for the Orlando strain; consumption tended to increase in each successive instar. Relative consumption rate (food consumed/cockroach/instar divided by the mean weight of the instar) was highest in the first two instars and decreased in subsequent instars.     

Developmental response of the brown-winged green bug, Plautia stali (Heteroptera: Pentatomidae), to food shortage

To study developmental response of the brown-winged green bug, Plautia stali Scott, to food shortage we reared nymphs under restricted feeding conditions produced by shortening the feeding period after molt or withholding food from second to fifth instars. For second instars, molting rates were significantly reduced as the feeding period was shortened. Shortening the feeding periods for third to fifth instars also reduced molting rates, but less so; some nymphs were able to complete their developments even if no food was given to any of the instars. Compared with controls for which feeding was not restricted, nymphs that successfully reached the next instar had reduced postmolt body size as a result of restricted feeding for all instars except the fifth (2-day feeding for second instar, and 1-day feeding for third and fourth instars), whereas instar duration was unchanged or only slightly prolonged for all instars. These results suggest that only nymphs with nutritional accumulation over a specific threshold in each instar can progress to the next instar, and that, particularly for second to fourth instars, nymphs develop on schedule without prolonging instar durations to compensate for reduced growth under conditions of food shortage.     

Sequence of ultrastructural changes induced by activation in the posterior neurosecretory cells in the brain of Rhodnius prolixus with special reference to the role of lysosomes.

The posterior neurosecretory cell (PNC) group in the brain of Rhodnius prolixus is composed of five ultrastructurally identical cells. The PNC were examined in the unfed fifth instar and at seven stages (from 15 min to 14 days) after activation was initiated by feeding. Each stage examined revealed successive changes in morphology which can be related to the synthesis, maturation, storage and transport of neurosecretory material. It is suggested, in particular, that the lysosomal system (dense bodies and multivesicular bodies) may play a role in the maturation of the secretory granules.     

Antipredator reaction norms for life history traits in Daphnia pulex: dependence on temperature and food

Synergistic effects between temperature and food level on the vulnerability of Daphnia life histories to predation have previously received little attention, despite their potential significance for summer population dynamics. In this investigation, most traits in the early life history of Daphnia pulex altered in response to increasing concentrations of fish kairomone. Although there was some variation attributable to experimental temperature and food treatments, traits exhibited reaction norms which suggested at least some degree of kairomone dose-dependence. Temperature, food level and their interaction affected the mean values of every trait examined and in some cases also influenced the antipredator response via a three-way interaction with fish kairomone. The insertion of an extra juvenile instar resulted in later maturation at a larger size for most females raised under conditions of low temperature and low food, but this response was largely suppressed in the presence of fish kairomone. Earlier maturation due to deletion of an instar was observed most frequently under high food and temperature conditions with fish kairomone present, suggesting an effect of kairomone on the size threshold for reproductive development. Principal components analysis was used to produce an index reflecting the net potential vulnerability to fish predation of the suite of life history traits. Vulnerability generally declined with increasing kairomone level as a result of the apparently adaptive alterations in most life history traits. Raised temperature and food level also generally reduced potential vulnerability, but a highly significant interaction between these factors was also found. Potentially important implications of these results for optimal vertical migration and summer population dynamics are discussed.     

Loss of the ecdysteroid-inducible E75A orphan nuclear receptor uncouples molting from metamorphosis in Drosophila

Isoform-specific null mutations were used to define the functions of three orphan members of the nuclear receptor superfamily, E75A, E75B, and E75C, encoded by the E75 early ecdysteroid-inducible gene. E75B mutants are viable and fertile, while E75C mutants die as adults. In contrast, E75A mutants have a reduced ecdysteroid titer during larval development, resulting in developmental delays, developmental arrests, and molting defects. Remarkably, some E75A mutant second instar larvae display a heterochronic phenotype in which they induce genes specific to the third instar and pupariate without undergoing a molt. We propose that ecdysteroid-induced E75A expression defines a feed-forward pathway that amplifies or maintains the ecdysteroid titer during larval development, ensuring proper temporal progression through the life cycle.     

三种蚤生殖系统发育的细微结构:雌性生殖腺的发育

本文研究的缓慢细蚤Leptopsylla segnis (Schonherr,1811),不等单蚤Monopsyllus anisus (Rotbschild,1907)和猫栉首蚤指名亚种Ctenocephalides felis felis (Bouchè,1835)均采自贵阳市区,鼠、猫宿主体上。通过饲养与繁殖,制作从三龄幼虫至成虫成熟各发育时间的连续切片。预察了各发育时间生殖腺发育的内部结构变化,依据卵巢芽的发育、分化,末端最大卵母细胞形态和大小的变化,卵泡上皮细胞形态和大小的变化,卵泡间组织的出现,卵黄的产生、积累及卵壳物质的分泌等,将雌性生殖腺的发育分为四期10个阶段,并对雌性生殖腺发育内部结构的变化,雌蚤卵黄沉淀初期的“空位现象”等进行了分析析和讨论。     

Food consumption by Chilo partellus (Lepidoptera: Pyralidae) larvae infected with Beauveria bassiana and Metarhizium anisopliae and effects of feeding natural versus artificial diets on mortality and mycosis

Second and third instar Chilo partellus larvae were infected with Beauveria bassiana and Metarhizium anisopliae (both at 1x10(8)conidia/ml) and daily consumption of maize leaves was measured. Infection by the fungi was associated with reduced mean daily food consumption. Reduction in food consumption became evident 3-4 days after treatment with the fungi for second instar larvae and 4-5 days for third instar larvae. Four conidial concentrations, 1x10(5), 1x10(6), 1x10(7), and 1x10(8)conidia/ml, were tested against second instar larvae. Food consumption dropped by 70-85% when the second instar larvae were treated with the fungi at 1x10(8)conidia/ml. Reduction in food consumption by C. partellus larvae infected with B. bassiana and M. anisopliae may offset the slow speed of kill of the fungi. The effect of artificial versus natural diets on mortality and mycoses of second instar larvae treated with the fungi at 1x10(8)conidia/ml was determined. Larvae provided with artificial diet suffered little mortality and mycoses than larvae provided with maize leaves. The LT(50) was longer for larvae provided with artificial diet.     

Prepupal diapause and instar IV developmental rates of the spruce beetle, Dendroctonus rufipennis (Coleoptera: Curculionidae, Scolytinae)

The spruce beetle, Dendroctonus rufipennis (Kirby), is an important mortality agent of native spruces throughout North America. The life-cycle duration of this species varies from 1 to 3 years depending temperature. The univoltine cycle (one generation per year) is thought to maximize outbreak risk and accelerate host mortality in established outbreaks. Prepupal diapause is associated with the semivoltine cycle (one generation per 2 years) and we investigated thermal conditions that result in diapause induction. Preliminary experiments used respirometry in an attempt to distinguish the diapause state of experimental insects but the technique was apparently confounded by low respiration before and during pupation, regardless of diapause status. Therefore, diapause induction was deduced using developmental delays. The observed developmental response was not a “switch”, with developmental delay either present or absent, but instead varied continuously. We found that temperatures <15 °C from instar III through mid-instar IV were associated with developmental delays beyond that expected from cool temperatures. Moreover, the duration of exposure to cool temperatures was important in determining the degree of developmental delay. Small, if any, delays were observed if the cumulative exposure to <15 °C was <20 d whereas >40 d cumulative exposure was associated with distinct developmental suppression. Intermediate exposure to cool temperatures resulted in minor developmental delays. We used our results to parameterize a maximum likelihood estimation model of temperature-dependent instar IV developmental rates, including the effect of diapause. This model can be included as part of a spruce beetle phenology model for predicting population dynamics.