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Abstract: The last 10 years have seen more research on insect macroevolution than all the previous years combined. Here, I summarize and criticise the claims that have been made by comparative phylogenetic and fossil studies, and identify some future opportunities. We know the fossil record and phylogeny of insects much better than we did 10 years ago. We cannot simply ascribe the richness of insects, or their subtaxa, to either age or diversification rate. There is evidence that fossil family richness peaked much earlier than previously suspected. Phylogenetic evidence, however, suggests that species‐level net diversification rates are accelerating, though this is highly variable across taxa, implying ongoing changes in global taxonomic composition. Although there is evidence that wings and metamorphosis have had some macroevolutionary effects, the most definitive broad phylogenetic study does not suggest that they directly elevated net diversification of species. There is little evidence that insect body size influences net diversification rate. Compared to other phyla, arthropod richness, of which insects comprise the major part, is best explained by non‐marine habit, presence of parasitic lifestyles, a skeleton, vision, and dioecy. Herbivory cannot yet robustly be said to increase diversification over other diets across all insects: there are contrary analyses, and effects differ in different taxa. Many phylogenetic studies now document how it sometimes does: from co‐speciation, to diffuse co‐evolution with host shifting. The last decade has shown that climate change and biogeographic processes are likely important in generating or limiting insect diversification, but there is a need for greater statistical rigour in such studies. There is also a need to understand the validity of some widely used statistical methods better, and to make better use of the data and methods that exist. Macroevolutionary entomology could greatly benefit from online data integration platforms to facilitate analyses of broader scope. [ABSTRACT FROM AUTHOR]

The first and last occurrences of hexapod families in the fossil record are compiled from publications up to end-2009. The major features of these data are compared with those of previous datasets (1993 and 1994). About a third of families (>400) are new to the fossil record since 1994, over half of the earlier, existing families have experienced changes in their known stratigraphic range and only about ten percent have unchanged ranges. Despite these significant additions to knowledge, the broad pattern of described richness through time remains similar, with described richness increasing steadily through geological history and a shift in dominant taxa, from Palaeoptera and Polyneoptera to Paraneoptera and Holometabola, after the Palaeozoic. However, after detrending, described richness is not well correlated with the earlier datasets, indicating significant changes in shorter-term patterns. There is reduced Palaeozoic richness, peaking at a different time, and a less pronounced Permian decline. A pronounced Triassic peak and decline is shown, and the plateau from the mid Early Cretaceous to the end of the period remains, albeit at substantially higher richness compared to earlier datasets. Origination and extinction rates are broadly similar to before, with a broad decline in both through time but episodic peaks, including end-Permian turnover. Origination more consistently exceeds extinction compared to previous datasets and exceptions are mainly in the Palaeozoic. These changes suggest that some inferences about causal mechanisms in insect macroevolution are likely to differ as well. [ABSTRACT FROM AUTHOR]

Ecology Letters (2010) 13: 383–393 The extent to which behavioural choices reflect fine-tuned evolutionary adaptation remains an open debate. For herbivorous insects, the preference–performance hypothesis (PPH) states that female insects will evolve to oviposit on hosts on which their offspring fare best. In this study, we use meta-analysis to assess the balance of evidence for and against the PPH, and to evaluate the role of individual factors proposed to influence host selection by female insects. We do so in an explicitly bitrophic context (herbivores versus plants). Overall, our analyses offer clear support for the PPH: Offspring survive better on preferred plant types, and females lay more eggs on plant types conducive to offspring performance. We also found evidence for an effect of diet breadth on host choice: female preference for ‘good quality plants’ was stronger in oligophagous insects than in polyphagous insects. Nonetheless, despite the large numbers of preference–performance studies conducted to date, sample sizes in our meta-analysis are low due to the inconsistent format used by authors to present their results. To improve the situation, we invite authors to contribute to the data base emerging from this work, with the aim of reaching a strengthened synthesis of the subject field. [ABSTRACT FROM AUTHOR]

Over half of all described species are insects, but until recently our understanding of the reasons for this diversity was based on very little macroevolutionary evidence. Here I summarize the hypotheses that have been posed, tests of these hypotheses and their results, and hence identify gaps in knowledge for future researchers to pursue. I focus on inferences from the following sources: (i) the fossil record, normally at family level, and (ii) insect phylogenies, sometimes combined with: (iii) the species richness of insect higher taxa, and (iv) current extinction risks. There is evidence that the species richness of insects has been enhanced by: (i) their relative age, giving time for diversification to take place; (ii) low extinction rates. There is little evidence that rates of origination have generally been high or that there are limits on numbers of species. However, the evidence on macroevolutionary rates is not yet so extensive or coherent as to present unequivocal messages. As regards morphological, ecological, or behavioural hypotheses, there is evidence that diversity has been enhanced by (iii) flight or properties resulting from it like enhanced dispersal, (iv) wing folding, and (v) complete metamorphosis. However, in all these cases the evidence is somewhat equivocal, either because of statistical issues or because evidence from different sources is conflicting. There is extensive evidence that diversity is affected by (vi) the ecological niche. Comparative studies indicate that phytophagy generally increases net diversification rates, and reduces extinction risk. However, niche specialization is also associated with an increase in extinction risk. Small body size (vii) is often associated with low extinction risk in comparative studies, but as yet there is no solid evidence that it consistently enhances net rates of diversification. Mouthpart diversity (viii) has generally increased over time in the insects, but cannot explain the apparent great increase in diversity seen in the Cretaceous and Tertiary. Sexual selection and sexual conflict (ix) are two processes that are widespread in insects, and there is comparative evidence linking both to increased diversification. Although some comparative evidence links tropical distributions (x) to increased rates of diversification, the extent to which latitudinal richness gradients are unusual in insects is equivocal. There is little to no direct evidence from fossils and phylogenies that insect diversity has generally been affected by (i) sensory- or neuro-sophistication, (ii) population size or density, (iii) generation time or fecundity, (iv) the presence of an exoskeleton or cuticle, (v) segmentation or appendage diversity, (vi) adaptability or genetic versatility, though all of these remain plausible hypotheses awaiting further tests. The data suggest that the insect body ground plan itself had no direct effect on insect diversity. Thus, whilst studies to date have given substantial understanding, substantial gaps still remain. Future challenges include: (i) interpreting conflicting messages from different sources of data; (ii) rating the importance of different hypotheses that are statistically supported; (iii) linking specific proximate to specific ultimate explanations and vice versa; and (iv) understanding how different ultimate hypotheses might be dependent on each other. [ABSTRACT FROM AUTHOR]

Behavioural interactions among relatives may have consequences for many other traits. We tested the hypothesis that solitary parasitoids (displaying siblicidal behaviour in their larvae) have narrower host ranges than gregarious parasitoids (with tolerant larvae). In laboratory experiments, we compared parasitization success in two sister species of braconid wasp [ Aphaereta genevensis (Fischer), solitary, and Aphaereta pallipes (Say), gregarious (Hymenoptera: Braconidae: Alysiini)] on eight Drosophila species or strains. Host species or strain was the most important factor affecting parasitization success, and some of this variation was accountable to host physiological defences. Although two hosts were more suitable for the solitary species, and one more suitable for the gregarious species, these differences were small, and there was no consistent difference across all hosts. Wasp body size was positively correlated with parasitization success in both wasp species. This may be because body size increases oviposition success, or the motivation to oviposit. In A. pallipes parasitization success peaked after 3–4 days, but later in A. genevensis. This is likely due to low life expectancy and high egg loads increasing oviposition tendency in young A. pallipes, and egg limitation decreasing oviposition tendency in old A. pallipes. These data suggest that interactions among wasp larvae do not greatly affect the size of the fundamental niche examined here. However, they show the potential for life history traits, which differ between the species as a likely consequence of larval interactions, to affect the extent of the realized niche. [ABSTRACT FROM AUTHOR]

I present a novel descriptive (non-statistical) method to help identify the location and importance of shifts in diversification across a phylogeny. The method first estimates radiation rates across terminal higher taxa and then subjects these rates to a parsimony analysis across the phylogeny. The reconstructions define the magnitude, direction and influence of past shifts in realized diversification rates across nodes. I apply the method to data on the extant hexapod orders. The results indicate that the Coleoptera (beetles) and Diptera (flies) have contributed large upward shifts in diversification tendency, without which, under the model employed, global species richness would be reduced by 20% and 6%, respectively. The origin of Neoptera (insects with wing flexion), identified elsewhere as a significant radiation, may represent a large positive, a large negative or zero influence on current species richness, depending on the assumed phylogeny and parsimony method. The most influential radiations are attributable to the origin of the Eumetabola (insects with complete metamorphosis plus bugs and their relatives) and Pterygota (winged insects), but there is presently only weak evidence that they represent significant shifts in underlying diversification tendency. These analyses support some but not all results of previous phylogenetic analyses and the identity of the most important shift therefore remains elusive. New methodology involving comparisons across multiple taxa is likely to be necessary. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 23–36. [ABSTRACT FROM AUTHOR]

Background: Skewed body size distributions and the high relative richness of small-bodied taxa are a fundamental property of a wide range of animal clades. The evolutionary processes responsible for generating these distributions are well described in vertebrate model systems but have yet to be explored in detail for other major terrestrial clades. In this study, we explore the macro-evolutionary patterns of body size variation across families of Hexapoda (insects and their close relatives), using recent advances in phylogenetic understanding, with an aim to investigate the link between size and diversity within this ancient and highly diverse lineage. Results: The maximum, minimum and mean-log body lengths of hexapod families are all approximately log-normally distributed, consistent with previous studies at lower taxonomic levels, and contrasting with skewed distributions typical of vertebrate groups. After taking phylogeny and within-tip variation into account, we find no evidence for a negative relationship between diversification rate and body size, suggesting decoupling of the forces controlling these two traits. Likelihood-based modeling of the log-mean body size identifies distinct processes operating within Holometabola and Diptera compared with other hexapod groups, consistent with accelerating rates of size evolution within these clades, while as a whole, hexapod body size evolution is found to be dominated by neutral processes including significant phylogenetic conservatism. Conclusions: Based on our findings we suggest that the use of models derived from well-studied but atypical clades, such as vertebrates may lead to misleading conclusions when applied to other major terrestrial lineages. Our results indicate that within hexapods, and within the limits of current systematic and phylogenetic knowledge, insect diversification is generally unfettered by size-biased macro-evolutionary processes, and that these processes over large timescales tend to converge on apparently neutral evolutionary processes. We also identify limitations on available data within the clade and modeling approaches for the resolution of trees of higher taxa, the resolution of which may collectively enhance our understanding of this key component of terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

1. Parasitoid wasps are species-rich and likely to be sensitive indicators of environmental change. Malaise traps are widely used for sampling certain taxa of parasitic Hymenoptera, but little is known about how they should best be used to monitor the community at an individual site. 2. To investigate the effects of sample duration, trap location and replication on the parasitoid assemblage, we sampled four ichneumonid subfamilies (Hymenoptera: Ichneumonidae) intensively using Malaise traps in two farm woods in the Vale of York, UK. 3. Species accumulation curves showed that even with 16 Malaise traps per wood, the community is incompletely sampled. Despite this, we caught up to 28% of all UK species in a single wood, implying that local parasitoid diversity may be very high. 4. Abundance and species richness of parasitoids differed significantly between sample periods (fortnights) and between traps, but did not differ overall between core and edge locations. 5. Parasitoid community composition differed between core and edge traps, but differences were much stronger in one wood than the other. One subfamily, the Poemeniinae, was found predominantly in edge locations. Catch differences became greater with increasing distance between traps. 6. The previous year, two traps in each of the same woods caught only half as many species, but species abundance was positively correlated between years. 7. Our results suggest that a small number of traps can contain useful information about the parasitoid community but is likely to seriously underestimate total species richness. To achieve extensive species coverage, sampling should continue over several weeks, with widely separated traps sampling both core and edge locations. Our focal taxa should prove excellent for monitoring the effects of environmental change on biodiversity. [ABSTRACT FROM AUTHOR]

1. Insect parasitoids comprise a large fraction of terrestrial biodiversity. Because of this diversity, species-level conservation of most parasitoid species is impractical and habitat conservation must substitute. However, habitat indicators of parasitoid abundance and diversity are poorly known. 2. To identify such habitat indicators, parasitoid wasps in four ichneumonid subfamilies were sampled in the field herb layer of 15 woodlands in the Vale of York, UK, using Malaise traps. The catch was related to vegetation characteristics. 3. A total of 1543 individuals in 60 species was recorded, representing 36% of UK species in the taxa sampled. Parasitoids tended to be more abundant and species rich in woodlands with a high broadleaf content and tree species richness. This pattern was observed in the ichneumonid subfamilies Pimplinae, Poemeniinae and Diacritinae. 4. However, the ichneumonid subfamily Diplazontinae was found to vary in abundance and richness within rather than between woodlands and showed no association with measured habitat variables. 5. Reserve selection analyses indicated that coniferous woodlands, and woodlands with a low abundance and richness of parasitoids, none the less can contribute to maximizing parasitoid diversity at the landscape scale. 6. Synthesis and applications. At the individual woodland scale, broadleaved woodlands with high tree species richness appear best for conserving parasitoid abundance and diversity. At a landscape scale however, a variety of woodland habitat types can maximize diversity of all parasitoid taxa. We hypothesize that the degree of association between parasitoid abundance and diversity, and characteristics of the vegetation within habitats will decrease with an increase in the number of trophic links that separate them. [ABSTRACT FROM AUTHOR]

Trends in insect abundance are well established in some datasets, but far less is known about how abundance measures translate into biomass trends. Moths (Lepidoptera) provide particularly good opportunities to study trends and drivers of biomass change at large spatial and temporal scales, given the existence of long‐term abundance datasets. However, data on the body masses of moths are required for these analyses, but such data do not currently exist.To address this data gap, we collected empirical data in 2018 on the forewing length and dry mass of field‐sampled moths, and used these to train and test a statistical model that predicts the body mass of moth species from their forewing lengths (with refined parameters for Crambidae, Erebidae, Geometridae and Noctuidae).Modeled biomass was positively correlated, with high explanatory power, with measured biomass of moth species (R2 = 0.886 ± 0.0006, across 10,000 bootstrapped replicates) and of mixed‐species samples of moths (R2 = 0.873 ± 0.0003), showing that it is possible to predict biomass to an informative level of accuracy, and prediction error was smaller with larger sample sizes.Our model allows biomass to be estimated for historical moth abundance datasets, and so our approach will create opportunities to investigate trends and drivers of insect biomass change over long timescales and broad geographic regions. [ABSTRACT FROM AUTHOR]

Explaining variation in life histories remains a major challenge because they are multidimensional and there are many competing explanatory theories and paradigms. An influential concept in life-history theory is the fast-slow continuum, exemplified by mammals. Determining the utility of such concepts across taxonomic groups requires comparison of the groups' life histories in multidimensional space. Insects display enormous species richness and phenotypic diversity, but testing hypotheses like the fast-slow continuum has been inhibited by incomplete trait data. We use phylogenetic imputation to generate complete data sets of seven life-history traits in orthopterans (grasshoppers and crickets) and examine the robustness of these imputations for our findings. Three phylogenetic principal components explain 83%–96% of variation in these data. We find consistent evidence of an axis mostly following expectations of a fast-slow continuum, except that "slow" species produce larger, not smaller, clutches of eggs. We show that the principal axes of variation in orthopterans and reptiles are mutually explanatory, as are those of mammals and birds. Essentially, trait covariation in Orthoptera, with "slow" species producing larger clutches, is more reptilelike than mammal-like or birdlike. We conclude that the fast-slow continuum is less pronounced in Orthoptera than it is in birds and mammals, reducing the universal relevance of this pattern and the theories that predict it. [ABSTRACT FROM AUTHOR]

The conditions required by rare species are often only approximately known. Monitoring such species over time can help refine management of their protected areas. We report population trends of a rare moth, the Dark Bordered Beauty Epione vespertaria (Linnaeus, 1767) (Lepidoptera: Geometridae) at its last known English site on a protected lowland heath, and those of its host-plant, Salix repens (L.) (Malpighiales: Salicaceae). Between 2007 and 2014, adult moth density reduced by an average of 30–35% annually over the monitored area, and its range over the monitored area contracted in concert. By comparing data from before this decline (2005) with data taken in 2013, we show that the density of host-plants over the monitored area reduced three-fold overall, and ten-fold in the areas of highest host-plant density. In addition, plants were significantly smaller in 2013. In 2005, moth larvae tended to be found on plants that were significantly larger than average at the time. By 2013, far fewer plants were of an equivalent size. This suggests that the rapid decline of the moth population coincides with, and is likely driven by, changes in the host-plant population. Why the host-plant population has changed remains less certain, but fire, frost damage and grazing damage have probably contributed. It is likely that a reduction in grazing pressure in parts of the site would aid host-plant recovery, although grazing remains an important site management activity. Our work confirms the value of constant monitoring of rare or priority insect species, of the risks posed to species with few populations even when their populations are large, of the potential conflict between bespoke management for species and generic management of habitats, and hence the value of refining our knowledge of rare species’ requirements so that their needs can be incorporated into the management of protected areas. [ABSTRACT FROM AUTHOR]

Explaining the taxonomic richness of the insects, comprising over half of all described species, is a major challenge in evolutionary biology. Previously, several evolutionary novelties (key innovations) have been posited to contribute to that richness, including the insect bauplan, wings, wing folding and complete metamorphosis, but evidence over their relative importance and modes of action is sparse and equivocal. Here, a new dataset on the first and last occurrences of fossil hexapod (insects and close relatives) families is used to show that basal families of winged insects (Palaeoptera, e.g. dragonflies) show higher origination and extinction rates in the fossil record than basal wingless groups (Apterygota, e.g. silverfish). Origination and extinction rates were maintained at levels similar to Palaeoptera in the more derived Polyneoptera (e.g. cockroaches) and Paraneoptera (e.g. true bugs), but extinction rates subsequently reduced in the very rich group of insects with complete metamorphosis (Holometabola, e.g. beetles). Holometabola show evidence of a recent slow-down in their high net diversification rate, whereas other winged taxa continue to diversify at constant but low rates. These data suggest that wings and complete metamorphosis have had the most effect on family-level insect macroevolution, and point to specific mechanisms by which they have influenced insect diversity through time. [ABSTRACT FROM AUTHOR]

Insects and their six-legged relatives (Hexapoda) comprise more than half of all described species and dominate terrestrial and freshwater ecosystems. Understanding the macroevolutionary processes generating this richness requires a historical perspective, but the fossil record of hexapods is patchy and incomplete. Dated molecular phylogenies provide an alternative perspective on divergence times and have been combined with birth-death models to infer patterns of diversification across a range of taxonomic groups. Here we generate a dated phylogeny of hexapod families, based on previously published sequence data and literature derived constraints, in order to identify the broad pattern of macroevolutionary changes responsible for the composition of the extant hexapod fauna. The most prominent increase in diversification identified is associated with the origin of complete metamorphosis, confirming this as a key innovation in promoting insect diversity. Subsequent reductions are recovered for several groups previously identified as having a higher fossil diversity during the Mesozoic. In addition, a number of recently derived taxa are found to have radiated following the development of flowering plant (angiosperm) floras during the mid-Cretaceous. These results reveal that the composition of the modern hexapod fauna is a product of a key developmental innovation, combined with multiple and varied evolutionary responses to environmental changes from the mid Cretaceous floral transition onward. [ABSTRACT FROM AUTHOR]