Insect Size Research Articles

Evolution of reduced minimum critical size as a response to selection for rapid pre-adult development in Drosophila melanogaster.

Adult body size in holometabolus insects is directly proportional to the time spent during the larval period. The larval duration can be divided into two parts: (i) pre-critical duration—time required to attain a critical size/critical weight that would result in successful completion of development and metamorphosis even under non-availability of nutrition beyond the time of attainment of critical size, and (ii) post-critical duration—the time duration from the attainment of critical size till pupation. It is of interest to decipher the relative contribution of the two larval growth phases (from the hatching of the egg to the attainment of critical size, and from the attainment of critical size to pupation) to the final adult size. Many studies using Drosophila melanogaster have shown that selecting populations for faster development results in the emergence of small adults. Some of these studies have indirectly reported the evolution of smaller critical size. Using two kinds of D. melanogaster populations, one of which is selected for faster/accelerated pre-adult development and the other their ancestral control, we demonstrate that the final adult size is determined by the time spent as larvae post the attainment of critical size despite having increased growth rate during the second larval instar. Our populations under selection for faster pre-adult development are exhibiting adaptive bailout due to intrinsic food limitation as against extrinsic food limitation in the yellow dung fly.

Differential Ability of Necrophagous Diptera to Colonize Concealed Resources: Empirical Evidence From a Field Experiment in Brazil.

Field studies in forensic entomology seem to assume that a cadaver is a resource equally accessible to flies, irrespective of the species' size, behavior, and sensorial capacity. We aimed to challenge this assumption by experimentally manipulating baited traps in order to test whether the accessibility to decomposing baits is related to the following: (i) the diversity of necrophagous dipterans; (ii) the body size of adults; and (iii) the female sexual maturity stage. The experiment was performed in a rainforest fragment in Northeastern Brazil, in an area characterized by high levels of homicides. Traps baited with decomposing chicken liver had three levels of access: easy (six openings on the trap), intermediate (three), and difficult (one). A total of 750 adults of Calliphoridae, Fanniidae, Muscidae, Phoridae, and Sarcophagidae were collected. Of the 18 species recorded, Megaselia scalaris was the most abundant (46.8%) followed by Lucilia eximia (29.7%) and Chrysomya megacephala (9.8%). The number of species increased significantly with the accessibility level, but overall abundance did not differ, as a consequence of the numerical dominance of M. scalaris. A strong female bias (>91%) was observed in all traps. For Calliphoridae specimens, 90% of the females caught in traps under intermediate and difficult access were sexually mature. By empirically demonstrating that limitation of access and exclusion of visual stimuli do not deter several dipteran species from reaching a substrate, we expand the knowledge on the factors that can shape the colonization of concealed human cadavers, including variables such as insect size and stage of sexual maturity.

How to be a Giant: Hypermetric Scaling of the Leg in Cockroaches and Scarab Beetles Suggests Oxygen Transport to the Legs Limits Maximal Insect Size

Understanding the causes and consequences of the evolution of large or small body size remains one of the important challenges of evolutionary biology. Insects have an unusual respiratory system, transporting oxygen in the gas phase via air‐filled tracheae. The possession of this unique system has been hypothesized to limit insect size, but how the morphology of the tracheal system changes as insects vary in size is still poorly known. Based on comparisons with vertebrates, we expect either geometric isometry in scaling (as found in lungs) or hypometric scaling (as found in vertebrate capillaries), with the latter matching the hypometric scaling of metabolic rate found for most animals. We tested these expectations by measuring the 3D morphology of tracheal systems of ten species each of cockroaches and scarab beetles. In both groups, body mass varied by more than an order of magnitude across species, which included some of the largest extant species of insect. Cockroaches were imaged at Argonne National Laboratory using synchrotron x‐ray microcomputed tomography (SR‐μCT), and scarab beetles were imaged at Virginia Tech using tabletop μCT. We measured the fraction of body volume occupied by the tracheal system for the major body compartments. In general, the tracheal system scaled isometrically in the head, thorax, and abdomen. However, within the legs, tracheal volume scaled strongly hypermetrically, resulting from an increase in number (in roaches) and size (in scarabs) of tracheae and/or air sacs. These data strongly suggest that evolution of larger species of insects requires increased relative investment in the tracheal system of the legs to overcome the challenges of long‐distance transport to muscles and nerves located in these long, blind‐ended structures, limiting the maximal size of insects.Support or Funding InformationSupported by NSF IOS 1122157 and IOS 1558052.

Breaking down insect stoichiometry into chitin-based and internal elemental traits: Patterns and correlates of continent-wide intraspecific variation in the largest European saproxylic beetle

Stoichiometric, trophic and ecotoxicological data have traditionally been acquired from patterns of variation in elemental traits of whole invertebrate bodies, whereas the critical issue of the extracellular origin of some portion of elements, such as those present in ingested food and internal organs, has been ignored. Here we investigated an unexplored, yet crucial, question relating to whether, and to what degree, metals from two major body fractions: exoskeleton (elytra) and internal (body organs with gut material present in abdomens), are correlated with each other in wild populations of the largest European saproxylic insect, the Stag Beetle Lucanus cervus, and how metals from these two fractions vary with insect size and local habitat conditions. We examined the continent-wide variation in the concentrations of 12 chemical elements (Ca, Mg, K, Na, Mn, Fe, Zn, Cu, As, Cd, Pb and Ni) measured in the elytra and abdomen of specimens from 28 populations inhabiting an urban-woodland habitat gradient across the species’ entire distributional range from Spain to Russia. Across populations, elemental concentrations (except Ni and Pb) were 2–13 times higher in abdominal samples than in elytra, and the magnitude of these differences was related to both insect size and local habitat conditions. Smaller individuals from both woodland and urban habitat tended to have higher concentrations of trace elements (Zn, As, Cd, Pb and Ni). The concentration of only six elements (Mg, K, Na, Mn, Cd and Ni) was correlated in the elytra and abdomen at the individual and population levels, implying a limitation to the broader applicability of elytra as a surrogate for internal elemental pools. We highlight that in non-feeding adult saproxylic beetles, minerals, acquired during the larval stage, may be concentrated in the large quantities of residual body fat.

Understanding the Evolutionary Ecology of host--pathogen Interactions Provides Insights into the Outcomes of Insect Pest Biocontrol.

The use of viral pathogens to control the population size of pest insects has produced both successful and unsuccessful outcomes. Here, we investigate whether those biocontrol successes and failures can be explained by key ecological and evolutionary processes between hosts and pathogens. Specifically, we examine how heterogeneity in pathogen transmission, ecological and evolutionary tradeoffs, and pathogen diversity affect insect population density and thus successful control. We first review the existing literature and then use numerical simulations of mathematical models to further explore these processes. Our results show that the control of insect densities using viruses depends strongly on the heterogeneity of virus transmission among insects. Overall, increased heterogeneity of transmission reduces the effect of viruses on insect densities and increases the long-term stability of insect populations. Lower equilibrium insect densities occur when transmission is heritable and when there is a tradeoff between mean transmission and insect fecundity compared to when the heterogeneity of transmission arises from non-genetic sources. Thus, the heterogeneity of transmission is a key parameter that regulates the long-term population dynamics of insects and their pathogens. We also show that both heterogeneity of transmission and life-history tradeoffs modulate characteristics of population dynamics such as the frequency and intensity of “boom–bust" population cycles. Furthermore, we show that because of life-history tradeoffs affecting the transmission rate, the use of multiple pathogen strains is more effective than the use of a single strain to control insect densities only when the pathogen strains differ considerably in their transmission characteristics. By quantifying the effects of ecology and evolution on population densities, we are able to offer recommendations to assess the long-term effects of classical biocontrol.

Swarms of Grasshoppers Invade Las Vegas

Swarms of Grasshoppers Invade Las Vegas Amelia Martens (bio) "Vast swarms of the insects are being drawn to the neon lights of Sin City—but they are not dangerous." -BBC News July 31, 2019 We are dangerous, we climbthirty-two stories, breakout windows and aim:our arms fullof automatic rifles. We glitter with brokenglass and we blockadedoorways for time;we angle more bulletsat the fish in our barrel,who people this parking lot. We are not attractedto neon, but to the newsinfamy is a type of love:an infinite tattoounexplainable, a truth. We drag bodies downto concrete, grass,asphalt, with holesthe size of insects;blood buzz heartssearch out a new queen. We are dangerous: we dieand return; we die andspread; we die andswarm; we die andeat the nest we warm. [End Page 35] Amelia Martens Amelia Martens is the author of The Spoons in the Grass are There To Dig a Moat (Sarabande Books, 2016), and four chapbooks. In 2019, she received an Al Smith Individual Artist Fellowship from the Kentucky Arts Council. She co-curates the Rivertown Reading Series, Exit 7, and two awesome daughters. Copyright © 2020 University of Wisconsin Board of Regents

The Benefit of a Single Oral Dose of Ivermectin in Humans: The Adverse Effects on Cimex lectularius L. Populations and Fecundity.

ObjectiveTo measure the population size and fecundity of the common bed bug Cimex lectularius L. (C. lectularius) after feeding it with the blood obtained from human subjects who have consumed a single dose of ivermectin.Methods Serial blood samples were obtained from two human subjects at hour 0 (control) and 4-96 hours after they received a single 0.2 mg/kg dose of ivermectin. The blood samples were then fed to 2,273 bed bugs. Bed bug incapacitation rates, fecundity, and population sizes were recorded over a 54-day period. Whole blood ivermectin levels were measured in the human subjects and the insects.Results The fold change in the size of the control group population over the course of the experiment was found to be 2.16. This was significantly greater (p: <.001) than for all the post-ivermectin feeding groups (range: -11.04-1.43). Two weeks after the experiment, the number of eggs laid per live adult female bed bug per day was 10.74 for controls, which was significantly different (p: <0.001) compared to all the post-ivermectin feeding groups (range: 0-4.28).Conclusions There were significant reductions in C. lectularius population size and fecundity in insects that fed on blood obtained from human study subjects up to 96 hours after they have consumed a single oral dose of ivermectin.

Size-based intraspecific variations along altitudinal gradient and follow of Bergmann’s rule in Parthenium beetle, Zygogramma bicolorata Pallister

Abstract Body size in insects is coupled with numerous physiological, life-history and ecological traits. Its variation along temperature gradient is widely studied. However, information regarding variations in body size of insects along altitudinal gradient is limited. Present study was designed considering hypothesis that there would be an increase in body size of Parthenium beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) with increasing altitude and decreasing in temperature. To achieve the objectives, beetles were collected from three eco-climatic zones of NEPAL [Kathmandu (1400 mts, 24 °C; warm temperate zone), Chitwan (415 mts, 25 °C; upper tropical/sub-tropical zone), and Mahendranagar (229 mts, 34 °C; humid subtropical zone)], and one of INDIA [Varanasi (81 mts, 36 °C; humid subtropical zone)] for their morphometric analysis (body length and body biomass). Results revealed that the size of beetles in all eco-climatic zones increased with increasing altitude and decreasing temperature. While adults of Kathmandu were largest, followed by Chitwan and Mahendranagar, but those of Varanasi were smallest in size. The sex ratio was female-biased in Kathmandu and Varanasi, but was male-biased in Chitwan and Mahendranagar. Irrespective of temperature and altitude, females were larger than males in all eco-climatic zones. Our results affirmed our hypothesis and were in compliance with Bergmann’s rule. The findings may be helpful in understanding phenotypic plasticity and distribution pattern of Z. bicolorata adults in Indian sub-continent under global climate change scenario.

Declines and Resilience of Communities of Leaf Chewing Insects on Missouri Oaks Following Spring Frost and Summer Drought

Extreme weather events dramatically impact populations of individual insect species but the consequences of such events for entire insect communities are not well documented. We present evidence that late spring frosts and summer drought negatively affect the community of insects found on Missouri oaks (Quercus alba and Q. velutina), amounting to a 23-186 fold decrease depending on the oak species, insect size and feeding guild, and the specific weather event. Spring faunas required three years or more following spring frosts to reach pre-event levels, whereas summer faunas were more resilient, rebounding within 1-2 years. The impact of summer drought on leaf tying caterpillars, however, lasted longer than that of the spring frost; it was five years before numbers of leaf ties reached pre-drought levels. Smaller species of leaf tying Lepidoptera took longer to recover than larger species following the drought. Overall, we found no evidence for a general decline in abundance, even a modest one, during the 20 years of study of faunas on oak trees in southeastern Missouri. However, the effects of drought reported here are likely to increase with time as the climate in the Midwest U.S. is only expected to become warmer and drier during the summer months. Similarly, the risk of late season frost damage to trees is expected to increase with predicted earlier onset of spring. Understanding the impact of such weather events on insect communities influences our ability to predict how habitat and landscape management, or lack thereof, will influence future patterns of insect abundance and diversity.

Macroecology of ground beetles: Species richness, range size and body size show different geographical patterns across a climatically heterogeneous area

AbstractAimEcogeographical patterns have been widely studied in endothermic vertebrates, but relatively few studies have simultaneously examined patterns and causes of gradients in species richness, range size and body size in ectothermic insects. We examined patterns in species richness, mean range size and mean body size of ground beetle assemblages across the biogeographical provinces of Northern Europe, a region that was mostly covered by ice sheets during the latest Ice Age and that presents strong contemporary climatic gradients.LocationNorthern Europe.MethodsWe used literature information on the occurrence of ground beetles, and analysed patterns in species richness, mean range size and mean body size across the provinces using generalized linear models and boosted regression tree (BRT) analysis.ResultsWe found a strongly decreasing gradient in species richness with increasing latitude, a strongly unimodal range size‐latitude relationship, and a weak unimodal body size‐latitude relationship in entire ground beetle assemblages. These gradients also varied among four major genera, suggesting that the overall patterns result from the nuances of smaller clades of ground beetles. The relative importance of contemporary environmental drivers also varied between species richness, mean range size and mean body size in BRT analysis. While species richness increased with mean annual temperature, mean range size showed an opposite relationship. Mean body size was most clearly associated with the precipitation of the driest month.Main ConclusionsOur findings showed that the latitudinal species richness gradient was strong, and it was closely related to concomitant variation in temperature, whereas variations in mean range size and mean body size were more complex. These findings suggest that the causes for range size and body size variation in insects may be complex, requiring additional insights from studies conducted at local, regional and continental scales.

Elevated temperatures translate into reduced dispersal abilities in a natural population of an aquatic insect

Rising global temperatures force many species to shift their distribution ranges. However, whether or not (and how fast) such range shifts occur depends on species' dispersal capacities. In most ecological studies, dispersal-related traits (such as the wing size or wing loading in insects) are treated as fixed, species-specific characteristics, ignoring the important role of phenotypic plasticity during insect development. We tested the hypothesis that dispersal-related traits themselves vary in dependence of ambient environmental conditions (temperature regimes, discharge patterns and biotic interactions during individual development). We collected data over 8years from a natural population of the crane fly Tipula maxima in central Germany. Using linear mixed-effect models, we analysed how phenotypic traits, phenological characteristics and population densities are affected by environmental conditions during the preceding 3, 6 and 12months. We found a moderate (5.6%) increase in wing length per 1°C increase in mean annual temperatures during the previous year. At the same time, body weight increased by as much as 17.8% in females and 26.9% in males per 1°C, likely driven by increased habitat productivity, which resulted in a 16.4% (female) and 19.3% (male) increased wing loading. We further found a shorter, more synchronized emergence period (i.e. a narrower time frame for dispersal) with increasing temperatures. Altogether, our results suggest that dispersal abilities of T.maxima were negatively affected by elevated temperatures, and we discuss how similar patterns might affect the persistence of populations of other aquatic insects, especially stenoecious taxa with narrow distribution ranges. Our study calls for integration of information on temperature-induced phenotypic plasticity of dispersal-related traits into models forecasting range shifts in the face of climate change. Furthermore, the patterns reported here are likely to affect metapopulation dynamics of aquatic insects under climate change conditions and may contribute to the ongoing decline of insect biomass and diversity.

Biological parameters, life table and thermal requirements of Thaumastocoris peregrinus (Heteroptera: Thaumastocoridae) at different temperatures

Temperature affects the development, population dynamics, reproduction and population size of insects. Thaumastocoris peregrinus Carpintero et Dellape (Heteroptera: Thaumastocoridae) is a eucalyptus pest. The objective of this study was to determine biological and life table parameters of T. peregrinus on Eucalyptus benthamii at five temperatures (18 °C; 22 °C; 25 °C; 27 °C and 30 °C) with a relative humidity (RH) of 70 ± 10% and photoperiod of 12 hours. The duration of each instar and the longevity of this insect were inversely proportional to the temperature, regardless of sex. The nymph stage of T. peregrinus was 36.4 days at 18 °C and 16.1 days at 30 °C. The pre-oviposition period was 5.1 days at 30 °C and 13.1 days at 18 °C and that of oviposition was 7.6 days at 30 °C and 51.2 days at 22 °C. The generation time (T) of T. peregrinus was 27.11 days at 22 °C and 8.22 days at 30 °C. Lower temperatures reduced the development and increased the life stage duration of T. peregrinus. Optimum temperatures for T. peregrinus development and reproduction were 18 and 25 °C, respectively.

Echolocating bats perceive natural-size targets as a unitary class using micro-spectral ripples in echoes.

Echolocating big brown bats emit frequency-modulated (FM) sounds covering ultrasonic frequencies in two harmonic sweeps (FM1 from 50-60 kHz sweeping down to 20-25 kHz, FM2 from 100-110 kHz sweeping down to 45 kHz). Using a complex interplay of acoustic cues, the bats perceive object distance from echo delay and object shape from echo spectra. Typical natural targets-flying insects-return discrete reflections, called glints, from prominent body parts (e.g., head, wings). Insect sizes are mostly 0.5 cm to about 3.5 cm, corresponding to reflected time separations of 30 to 210 μs. When closely spaced reflections overlap, they interfere to create a characteristic echo spectrum containing repetitive peaks and nulls. Time spacing of these glints (Δt) is transposed into spectral ripples at frequency intervals (Δf = 1/Δt) from about 30 kHz down to 5 kHz. The bat's perception of rippled echoes as a distinct class was tested in two-alternative forced-choice discrimination experiments with a standard stimulus of 100 μs glint separation (10 kHz ripples), in the middle of natural ripple separations (30 kHz to 5 kHz). Stimuli were electronically generated virtual targets with simulated 2-glint sizes from smaller than 0.5 cm to larger than 3.5 cm. Bats perceived insect-sized virtual objects (glint delays of 36-300 μs) as similar to the 100-μs standard, while smaller or larger virtual objects were perceived as not similar. Insect-sized echoes contained a pattern of microscale spectral ripples that stood apart from the coarser, macroscale spectral features of smaller objects or the temporally separate reflections of larger objects. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Within‐plant heterogeneity in fecundity and herbivory induced by localized DNA hypomethylation in the perennial herb Helleborus foetidus

Phenotypic heterogeneity of reiterated, homologous structures produced by individual plants has ecological consequences for plants and their animal consumers. This paper examines experimentally the epigenetic mosaicism hypothesis, which postulates that within-plant variation in traits of reiterated structures may partly arise from different parts of the same genetic individual differing in patterns or extent of genomic DNA methylation. Leaves of paired ramets borne by field-growing Helleborus foetidus plants were infiltrated periodically over the entire flowering period with either a water solution of the demethylating agent zebularine or just water as the control. The effects of the zebularine treatment were assessed by quantifying genome-wide DNA cytosine methylation in leaves and monitoring inflorescence growth and flower production, number of ovules per flower, pollination success, fruit set, seed set, seed size, and distribution of sap-feeding insects. Genomic DNA from leaves in zebularine-treated ramets was significantly less methylated than DNA from leaves in control ones. Inflorescences in treated ramets grew smaller and produced fewer flowers, with fewer ovules and lower follicle and seed set, but did not differ from inflorescences in untreated ramets in pollination success or seed size. The zebularine treatment influenced the within-plant distribution of sap-feeding insects. Experimental manipulation of genomic DNA methylation level in leaves of wild-growing H. foetidus plants induced considerable within-plant heterogeneity in phenotypic (inflorescences, flowers, fecundity) and ecologically relevant traits (herbivore distribution), which supports the hypothesis that epigenetic mosaicism may partly account for within-plant variation.

Identification of genes underlying phenotypic plasticity of wing size via insulin signaling pathway by network-based analysis in Sogatella furcifera

BackgroundPhenotypic plasticity is a common and highly adaptive phenomenon where the same genotype produces different phenotypes in response to environmental cues. Sogatella furcifera, a migratory pest of rice exhibits wing dimorphism, is a model insect for studying phenotypic plasticity of wing size. The Insullin-PI3K-Akt-FOXO signaling pathway plays a crucial role in the manipulation of wing size in the migratory insects. However, the regulatory mechanism via the pathway involved in wing dimorphism are still unexplored.ResultsAccompanied by special alternative splicing, genes involved in muscle contraction and energy metabolism were highly expressed in the wing hinges of macropters, demonstrating their adaptation for energy-demanding long-distance flights. Based on FOXO ChIP-Seq analysis, a total of 1259 putative target genes were observed in the wing hinges, including wing morph development, flight muscle and energy metabolism genes. An integrated gene interaction network was built by combining four heterogeneous datasets, and the IIS-PI3K-Akt-FOXO pathway was clustered in a divided functional module. In total, 45 genes in the module directly interacting with the IIS-PI3K-Akt-FOXO pathway showed differential expression levels between the two wing hinges, thus are regarded as potential Insulin pathway mediated wing dimorphism related genes (IWDRGs). Of the 45 IWDRGs, 5 were selected for verification by gene knockdown experiments, and played significant roles in the insect wing size regulation.ConclusionsWe provided valuable insights on the genetic basis of wing dimorphism, and also demonstrated that network analysis is a powerful approach to identify new genes regulating wing dimorphic development via insulin signaling pathway in the migratory insect.

Drosophila Acquires a Long-Lasting Body-Size Memory from Visual Feedback

Grasping an object or crossing a trench requires the integration of information on the operating distance of our limbs with precise distance estimation. The reach of our hands and step size of our legs are learned by the visual feedback we get during our actions. This implicit knowledge of our peripersonal space is first acquired during infancy but will be continuously updated throughout our whole life [1]. In contrast, body size of holometabolous insects does not change after metamorphosis; nevertheless, they do have to learn their body reaches at least once. The body size of Drosophila imagines can vary by about 15% depending on environmental factors like food quality and temperature [2]. To investigate how flies acquire knowledge about and memorize their body size, we studied their decisions to either refrain from or initiate climbing over gaps exceeding their body size [3]. Naive (dark-reared) flies overestimate their size and have to learn it from the parallax motion of the retinal images of objects in their environment while walking. Naive flies can be trained in a striped arena and manipulated to underestimate their size, but once consolidated, this memory seems to last for a lifetime. Consolidation of this memory is stress sensitive only in the first 2h after training but cannot be retrieved for the next 12 h. We have identified a set of intrinsic, lateral neurons of the protocerebral bridge of the central complex [4, 5] that depend on dCREB2 transcriptional activity for long-term memory consolidation and maintenance.

Changes in the Body Size of Carabid Beetles Along Elevational Gradients: A Multispecies Study of Between- and Within-Population Variation.

Geographic variation in body size has fascinated biologists since the 19th century as it can provide insight into the evolution of the body size of various organisms. In this study, we investigated body size variation in eight carabid species/subspecies (Coleoptera: Carabidae) along elevational gradients in six Central European mountain ranges. First, we examined elevational variation in body size and whether female and male body sizes differed in their responses to elevation. Second, we examined intrapopulation variation in body size along an elevational gradient, and we compared the degrees of intrapopulation variation between males and females. The investigated species either followed a converse Bergmann's cline (Carabus auronitens auronitens Fabricius 1792; Carabus linnei Panzer 1810; Pterostichus melanarius (Illiger, 1798); Pterostichus pilosus (Host, 1789)) or their size was unaffected by elevation (Carabus auronitens escheri Palliardi, 1825; Carabus sylvestris sylvestris Panzer, 1796; Carabus sylvestris transsylvanicus Dejean, 1826; Pterostichus burmeisteri Heer, 1838). Females were the larger sex in all the investigated species, but the degree of sexual size dimorphism differed between species. In general, the degree of sexual size dimorphism showed no change with elevation. The degree of intrapopulation variation in body size slightly increased with elevation in C. sylvestris sylvestris and P. pilosus. Overall, the intrapopulation variation in body size significantly differed among the investigated carabid species. The existing literature on intrapopulation variation in the body size of insects is limited, but further investigation of this issue could provide a better understanding of the mechanisms that generate geographical clines.

Upregulation of E93 Gene Expression Acts as the Trigger for Metamorphosis Independently of the Threshold Size in the Beetle Tribolium castaneum

Body size in holometabolous insects is determined by the size at which the juvenile larva undergoes metamorphosis to the pupal stage. To undergo larva-pupa transition, larva must reach a critical developmental checkpoint, the threshold size (TS); however, the molecular mechanisms through which the TS cues this transition remain to be fully characterized. Here, we use the flour beetle Tribolium castaneum to characterize the molecular mechanisms underlying entry into metamorphosis. We found that T.castaneum reaches a TS at the beginning of the last larval instar, which is associated with the downregulation of TcKr-h1 and the upregulation of TcE93 and TcBr-C. Unexpectedly, we found that while there is an association between TS and TcE93 upregulation, it is the latter that constitutes the molecular trigger for metamorphosis initiation. In light of our results, we evaluate the interactions that control the larva-pupa transition and suggest alternative models.

The quality of developmental reference data in forensic entomology: Detrimental effects of multiple, in vivo measurements in Creophilus maxillosus L. (Coleoptera: Staphylinidae)

Although in vivo measurements of larval insects are often performed during developmental studies of necrophilous beetles, their impact on development has not been studied. During measurements insects are taken out of the incubator for a few minutes at room temperature, which may affect the development and eventually the quality of the developmental reference data. Additionally, while being measured larvae are under stress which may have an effect on their development. We conducted an experiment using predatory beetle species Creophilus maxillosus L. (Coleoptera: Staphylinidae) which often occurs and breeds on large vertebrate carcasses. We tested the hypothesis that multiple, in vivo measurements affect the development of C. maxillosus by increasing its duration and changing adult insect size at emergence. As a consequence, we predicted that the multiple insect measurement protocol will affect the accuracy of age estimates using the resultant reference developmental data. Development of C. maxillosus was studied at 7 constant temperatures. All individuals were inspected for developmental landmarks; half of them were also repeatedly measured and weighed. Measured beetles developed longer than non-measured beetles (e.g. 1.59 days longer at 22.5 °C) and at emergence were distinctly smaller (e.g. 1.5 mm shorter and 22 mg lighter at 22.5 °C). The accuracy of age estimates was greater while using the model for non-measured beetles. These results support the claim that multiple in vivo measurements of insects reduce the quality of resultant developmental data. The measurements were particularly detrimental for the adult insect size. Consequently, particular attention should be paid to isomegalen diagrams which are based on insect length. Our findings indicate that these diagrams, when based on multiple, in vivo measurements of larval beetles, will systematically overestimate their age.

Variations in fecundity over catchment scales: Implications for caddisfly populations spanning a thermal gradient

Abstract Population sizes of stream insects depend on the number of eggs that enter the benthos. Densities of oviposited eggs have been linked to densities of oviposition habitat, but variability in fecundity has not been explored. Fecundity may differ between sites where females experience different thermal environments during development, because insects generally grow larger and produce more eggs in cold places (e.g. high elevation and latitude). We predicted that because the fecundity of emerging females should increase with elevation then the numbers of eggs in oviposited egg masses (clutch sizes) should also increase with elevation. Alternatively, individuals may routinely disperse along channels or between rivers, mixing individuals that have grown and developed in different thermal environments, in which case clutch sizes may not vary with elevation but could vary greatly within sites. We tested these hypotheses across an elevation gradient of 250–1,080 m above sea level, in seven streams in southeast Australia. We surveyed the fecundity of three species of caddisflies (Trichoptera: Hydrobiosidae) in 2009 (eight sites) and 2010 (17 sites). Female hydrobiosids attach their entire clutch of eggs to an emergent stream boulder, in a single egg mass. At each site we censused the number of egg masses in two random 50 m stretches and photographed a sample of egg masses. Clutch sizes were quantified by counting eggs from the photographs. From numbers of egg masses and mean clutch size per site, we estimated the number of individual eggs per site, to determine whether spatial differences in clutch size affect patterns of egg supply. Potential trade‐offs between egg number and size were also examined. Strong thermal gradients were observed in both years. Sites at lowest elevations were 4.8°C (2009) and 3.6°C (2010) warmer than sites at highest elevations, and accumulated 392 (2009) and 361 (2010) more degree‐days (&gt;0°C) over a period of 88 days. Clutch sizes of each species varied markedly within and between species but did not differ along the thermal gradient. Within species, 83.7–93.7% of variation in clutch size was expressed within sites. Relatively little variation occurred between sites or rivers. Within species, counts of egg masses adequately described relative egg supply to each site, because clutch sizes were similar between sites and rivers. Comparing egg supply between species, however, required including clutch sizes to estimate supply. Egg size differed within but not between species. Significant but small variations in egg size were trivial compared to much larger variations in clutch size. Our results suggest that any spatial differences in fecundity caused by temperature may be erased by dispersal, such that females from multiple locations mix between sites prior to oviposition. A warming global climate may reduce the fecundity of ectotherms such as aquatic insects but consequences for populations are difficult to predict. Moreover, climate‐related effects on fecundity may not be apparent when dispersal by individuals between elevations mixes any effects of climate change on fecundity.