As larvae, solitary species of parasitoid wasps eliminate rivals, including sibs, through contest... more As larvae, solitary species of parasitoid wasps eliminate rivals, including sibs, through contest competition. In gregarious species, larvae tolerate each other and several individuals can develop from a single host. We report experiments on two congeneric braconid species aimed at understanding how gregarious development evolved in one genus, and the consequences of larval interactions for parental behavior. In the transition from solitary to gregarious development, one possible intermediate stage is if solitary species frequently lay more than one egg per host. If the risk of conspecific superparasitism (another female of the same species oviposits into a single host) is high, optimal clutch size theory predicts the laying of multiple-egg clutches, because a female will increase the probability of the surviving larva being her own. Under the same conditions, theory predicts that gregarious species should reduce their clutch size. In our experiments, the solitary Aphaereta genevensis increased their clutch size under the risk of intraspecific competition for hosts whilst the gregarious A. pallipes reduced their clutch size, as predicted. In A. genevensis, the response to the risk of competition was dependent upon body size, being greatest amongst small females. In A. pallipes, the response did not depend on female body size, but clutch size increased with body size in all treatments, unlike in A. genevensis. Under the risk of competition from the other species, the response differed relative to the intraspecific treatments and differed be-tween species. Thus, our data suggest that: (1) competition for hosts may have contributed to the evolution of gregarious development in this genus; (2) female wasps can combine information from both external and internal cues in complex ways during clutch size adjustment; and (3) the social environment may alter the adaptive response to both external and internal cues in adult females.
We report experiments using two closely related species of alysiine braconids directed at underst... more We report experiments using two closely related species of alysiine braconids directed at understanding how gregarious development evolved in one subfamily of parasitoid wasps. Theoretical models predict that once siblicide between parasitoid wasps has evolved, it can only be lost under stringent conditions, making the transition from solitary to gregarious development exiguous. Phylogenetic studies indicate, however, that gregariousness has independently arisen on numerous occasions. New theoretical models have demonstrated that if gregarious development involves reductions in larval mobility, rather than a lack of fighting ability (as in the older models), the evolution of gregariousness is much more likely. We tested the predictions of the older tolerance models (gregariousness based on non-fighting larval phenotypes) and the reduced mobility models (gregariousness based on non-searching larval phenotypes) by observing larval movement and the outcome of interspecific competition between Aphaereta genevensis (solitary) and A. pallipes (gregarious) under multiparasitism. Differences in larval mobility matched the prediction of the reduced mobility model of gregarious development, with the solitary A. genevensis having larvae that are much more mobile. The proportion of hosts producing the solitary species significantly declined after subsequent exposure to females of the gregarious species. This contradicts the prediction of the older models (fighting vs non-fighting phenotypes), under which any competitive interactions between solitary and gregarious larvae will result in a highly asymmetrical outcome, as the solitary species should be competitively superior. The observed outcome of interspecific competition offers evidence, with respect to this subfamily, in favour of the new models (searching vs non-searching phenotypes).
Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps... more Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps due to the evolution of brood reduction behaviour in larvae competing for developmental resources. Despite this, many species of parasitoid wasp develop in small gregarious broods. Here, I catalogue the life-history properties of 87 such species, and attempt to explain their apparent stability in brood size. Small gregarious broods are taxonomically widespread, occurring in at least 15 of the 26 families containing gregarious species. The life-histories represented in this species list are extremely varied. Several species display properties consistent with an increase in the stability of non-siblicidal behaviour, but few of these properties are common to a large proportion of species. This suggests that either several factors contribute towards clutch size stability, or some important unknown variable is responsible. I discuss stochasticity in brood size as a novel but widespread factor contributing to the stability of non-siblicidal behaviour.
Entomologia Experimentalis Et Applicata, Oct 1, 2005
Behavioural interactions among relatives may have consequences for many other traits. We tested t... more 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.
Across animal species, body size and clutch size often form part of a suite of associated life hi... more Across animal species, body size and clutch size often form part of a suite of associated life history traits, exemplified by the ''fast Á/slow continuum'' in mammals. Across the parasitoid Hymenoptera however, a major axis of life history variation is the development mode of the larva (koinobiosis versus idiobiosis), and body size and clutch size do not seem to form clear associations with this major axis. Here we use a large comparative data set and the latest phylogenetic information to explore hypotheses that might explain the variation in body size and clutch size across species in parasitoids. We find evidence for three novel evolutionary correlations: changes in the stage of host attacked by the parasitoid (i.e. egg, larva, pupa) significantly predict changes in both body size and clutch size, whilst in gregarious species changes to higher latitudes are associated with reduced clutch size. We also find a number of hypothesized cross-species (phenotypic) associations that, however, we cannot demonstrate are the result of evolutionary correlations: large bodied species in our data tend to lay small clutches; koinobionts are larger than idiobionts attacking the same host stage; tropical species are smaller than temperate species (Bergmann's rule). Our results provide support for theoretical models of trait evolution in parasitoids, whilst the associations between latitude and life history may help explain why species richness in the family Ichneumonidae peaks at intermediate latitudes. Our results also show the continuing value of phylogenetically-based comparative analyses and demonstrate that recent work on parasitoid phylogenetics has produced significant benefits for our understanding of life history evolution.
The extent to which behavioural choices reflect fine-tuned evolutionary adaptation remains an ope... more 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 Ôgood quality plantsÕ 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.
The sex allocation strategy of the parasitoid Laelius pedatus (Hymenoptera: Bethylidae) on differ... more The sex allocation strategy of the parasitoid Laelius pedatus (Hymenoptera: Bethylidae) on differentsized hosts was investigated. The wasp lays from one to five eggs, and clutch size increases with host size. On the smallest hosts, single male eggs are laid, while on slightly larger hosts single female eggs are laid. On still larger hosts, gregarious clutches are laid which nearly always consist of a single male and one or more female eggs. The sex ratio strategy of the wasp appears to be influenced by a combination of local mate competition and conditional sex expression based on host quality.
Parasitoid wasps exhibit a stark dichotomy in larval behavior and developmental mode. In gregario... more Parasitoid wasps exhibit a stark dichotomy in larval behavior and developmental mode. In gregarious species, siblings developing together tolerate each other; hence more than one individual can successfully complete development. In contrast, solitary species have intolerant larvae that will engage in siblicide, leading to only one individual successfully completing development. Previous theoretical and empirical work has suggested that females from species with intolerant larvae should reduce their relative investment in reproduction. We tested this prediction by measuring investment in survival and reproduction in a pair of sister species from the genus Aphaereta (Hymenoptera: Braconidae). With increasing body size, divergent patterns of investment exist in the two species. Females of the solitary A. genevensis allocate additional resources almost exclusively toward greater fat reserves, resulting in enhanced longevity. Females of the gregarious A. pallipes invest relatively more in reproduction and hence have lower fat reserves, reduced longevity, and greater egg loads than A. genevensis. These differences reflect a trend toward greater investment in survival relative to reproduction in the solitary species, as predicted. We discuss the implications of these findings for the development of sibling rivalry and life-history theory.
Proceedings of The Royal Society B: Biological Sciences, Mar 7, 1998
Data are assembled on the clutch-size strategies adopted by extant species of parasitoid wasp. Th... more Data are assembled on the clutch-size strategies adopted by extant species of parasitoid wasp. These data are used to reconstruct the history of clutch-size evolution in the group using a series of plausible evolutionary assumptions. Extant families are either entirely solitary, both solitary and gregarious, or else clutch size is unknown. Parsimony analysis suggests that the ancestors of most families were solitary, a result which is robust to di¡erent phylogenetic relationships and likely data inadequacies. This implies that solitariness was ubiquitous throughout the initial radiation of the group, and that transitions to gregariousness have subsequently occurred a minimum of 43 times in several, but not all lineages. Current data suggest that species-rich and small-bodied lineages are more likely to have evolved gregariousness, and contain more species with small gregarious brood sizes. I discuss the implications of these data for clutchsize theory.
Deep time is geologic time, extending to the origin of the planet. For biologists in search of an... more Deep time is geologic time, extending to the origin of the planet. For biologists in search of an understanding of extinction, the relevant portion of deep time is that in which life has existed on the planet— about the last 4 billion years (Cowen, 2000). Extinctions are first recorded when the fossil record is robust enough to offer insights into the arrival and disappearance of groups of organisms (Benton and Harper, 2009). Extinctions in deep time can therefore be identified only over about the last 600 million years, an interval of time dominated by the Phanerozoic eon (540 million years ago to present).
Previously, theoretical and empirical studies suggested that parasitoids developing in small mult... more Previously, theoretical and empirical studies suggested that parasitoids developing in small multiple-egg broods would evolve siblicidal behaviour, making such brood sizes rare and single-egg broods an evolutionary absorbing state. Recent evidence, however, suggests that small gregarious broods are relatively stable in many parasitoid taxa, and that gregarious development has evolved many times from solitary development. This suggests that new research is needed to assess how nonsiblicidal behaviour can spread and become stable. We discuss some potentially rewarding possibilities.
Biological control efforts against the shore fly Scatella tenuicosta Collin, a pest of commercial... more Biological control efforts against the shore fly Scatella tenuicosta Collin, a pest of commercial glasshouses, have had limited success. The ability of one of its parasitoids, Aphaereta debilitata Morley, to control shore fly populations was investigated on lettuce crops within six experimental glasshouse units, over 26 weeks. The six shore fly populations, either with or without a single release of 150
bioRxiv (Cold Spring Harbor Laboratory), Jul 8, 2019
1. Insect abundance changes are well-established in some datasets, but far less is known about ho... more 1. Insect abundance changes are well-established in some datasets, but far less is known about how this translates into biomass changes. 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 for moths. This requires estimation of the body mass of moths sampled over time, but such data do not currently exist. 2. We collected empirical data in 2018 on the forewing length and dry mass of 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). We tested the relationships between biomass, abundance and species richness of samples of moths for our 2018 samples, and over a 16-year period using long-term historical moth data (with model-estimated biomass) from a single site. 3. Modelled biomass was positively correlated with measured biomass of moth species (R 2 = 0.910) and mixed-species samples of moths (R 2 = 0.915), showing that it is possible to predict biomass accurately. Biomass correlated with moth abundance and species richness in our 2018 data and in the historical dataset, revealing biomass declined by 65.9 % over a 16-year period. 4. By allowing biomass to be estimated for historical moth abundance datasets, our approach creates opportunities to investigate trends and drivers of insect biomass change over long timescales and broad geographic regions.
1. Several authors have proposed that inter-speci®c variation in parasitoid life histories can be... more 1. Several authors have proposed that inter-speci®c variation in parasitoid life histories can be classi®ed according to a dichotomy of development modes: ectoparasitoids and idiobionts with one suite of traits, and endoparasitoids and koinobionts with an opposing set of traits. 2. The factual evidence for such a dichotomy is presently scant. Here, 10 predictions of the dichotomous hypothesis are assessed using life history data from 474 species of parasitoid Hymenoptera. 3. A degree of support for the dichotomy is found. As predicted, koinobiosis is associated with endoparasitism, and idiobiosis with ectoparasitism. Endoparasitism and/or koinobiosis are also associated with a shorter adult lifespan, a shorter window for parasitism, smaller eggs, a longer pre-adult lifespan and, in larval parasitoids, a greater oviposition rate and fecundity than ectoparasitism/idiobiosis. 4. However, several predictions are not upheld by the data. No signi®cant relationship is found between development mode and either body size, the degree of host concealment or the stage of host attacked. Some trends are only found amongst larval parasitoids, and others do not hold for both endoparasitism and koinobiosis. 5. We conclude that there is at least some merit to the dichotomous hypothesis, though the most extensive depictions go beyond the present data. As a step towards formulating the dichotomy in a more rigid theoretical base, we discuss the selective pressures and constraints that are likely to account for the observed trends.
Bethylid wasps are a medium sized family o f parasitic Hymenoptera, with biological control poten... more Bethylid wasps are a medium sized family o f parasitic Hymenoptera, with biological control potential, which have recently proved excellent model systems for testing evolutionary and life history theory. We report observations on a species of Laelius from The Netherlands. The species is morphologically indistinguishable from Laelius pedatus, previously reported only from the N ew World. Reciprocal crosses between the Dutch wasps and L. pedatus from Madison, Wisconsin, U SA confirmed that the Dutch population belongs to L. pedatus. We compared the life history o f the Dutch wasps with those from Madison by rearing them on Trogoderma glabrum, but found no significant differences. The Dutch wasps successfully parasitize Trogoderma angustum, an invasive museum and domestic pest found in situ, but suffer high developmental mortality on T. glabrum. Wasp egg size was positively correlated with the size o f ovipositing female, which was also negatively correlated with the developmental mortality of offspring. Larger wasps also carried more mature eggs. Time taken to lay the clutch increased with the size o f the eventual clutch laid and was longer in unmated than mated females. When some wasps died before completing development, surviving members of the brood grew to a larger size and took longer to complete development. The number o f males per brood increased with previous oviposition experience, an indication o f sperm depletion through life. We discuss the implications o f these trends for parasitoid life history theory.
As larvae, solitary species of parasitoid wasps eliminate rivals, including sibs, through contest... more As larvae, solitary species of parasitoid wasps eliminate rivals, including sibs, through contest competition. In gregarious species, larvae tolerate each other and several individuals can develop from a single host. We report experiments on two congeneric braconid species aimed at understanding how gregarious development evolved in one genus, and the consequences of larval interactions for parental behavior. In the transition from solitary to gregarious development, one possible intermediate stage is if solitary species frequently lay more than one egg per host. If the risk of conspecific superparasitism (another female of the same species oviposits into a single host) is high, optimal clutch size theory predicts the laying of multiple-egg clutches, because a female will increase the probability of the surviving larva being her own. Under the same conditions, theory predicts that gregarious species should reduce their clutch size. In our experiments, the solitary Aphaereta genevensis increased their clutch size under the risk of intraspecific competition for hosts whilst the gregarious A. pallipes reduced their clutch size, as predicted. In A. genevensis, the response to the risk of competition was dependent upon body size, being greatest amongst small females. In A. pallipes, the response did not depend on female body size, but clutch size increased with body size in all treatments, unlike in A. genevensis. Under the risk of competition from the other species, the response differed relative to the intraspecific treatments and differed be-tween species. Thus, our data suggest that: (1) competition for hosts may have contributed to the evolution of gregarious development in this genus; (2) female wasps can combine information from both external and internal cues in complex ways during clutch size adjustment; and (3) the social environment may alter the adaptive response to both external and internal cues in adult females.
We report experiments using two closely related species of alysiine braconids directed at underst... more We report experiments using two closely related species of alysiine braconids directed at understanding how gregarious development evolved in one subfamily of parasitoid wasps. Theoretical models predict that once siblicide between parasitoid wasps has evolved, it can only be lost under stringent conditions, making the transition from solitary to gregarious development exiguous. Phylogenetic studies indicate, however, that gregariousness has independently arisen on numerous occasions. New theoretical models have demonstrated that if gregarious development involves reductions in larval mobility, rather than a lack of fighting ability (as in the older models), the evolution of gregariousness is much more likely. We tested the predictions of the older tolerance models (gregariousness based on non-fighting larval phenotypes) and the reduced mobility models (gregariousness based on non-searching larval phenotypes) by observing larval movement and the outcome of interspecific competition between Aphaereta genevensis (solitary) and A. pallipes (gregarious) under multiparasitism. Differences in larval mobility matched the prediction of the reduced mobility model of gregarious development, with the solitary A. genevensis having larvae that are much more mobile. The proportion of hosts producing the solitary species significantly declined after subsequent exposure to females of the gregarious species. This contradicts the prediction of the older models (fighting vs non-fighting phenotypes), under which any competitive interactions between solitary and gregarious larvae will result in a highly asymmetrical outcome, as the solitary species should be competitively superior. The observed outcome of interspecific competition offers evidence, with respect to this subfamily, in favour of the new models (searching vs non-searching phenotypes).
Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps... more Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps due to the evolution of brood reduction behaviour in larvae competing for developmental resources. Despite this, many species of parasitoid wasp develop in small gregarious broods. Here, I catalogue the life-history properties of 87 such species, and attempt to explain their apparent stability in brood size. Small gregarious broods are taxonomically widespread, occurring in at least 15 of the 26 families containing gregarious species. The life-histories represented in this species list are extremely varied. Several species display properties consistent with an increase in the stability of non-siblicidal behaviour, but few of these properties are common to a large proportion of species. This suggests that either several factors contribute towards clutch size stability, or some important unknown variable is responsible. I discuss stochasticity in brood size as a novel but widespread factor contributing to the stability of non-siblicidal behaviour.
Entomologia Experimentalis Et Applicata, Oct 1, 2005
Behavioural interactions among relatives may have consequences for many other traits. We tested t... more 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.
Across animal species, body size and clutch size often form part of a suite of associated life hi... more Across animal species, body size and clutch size often form part of a suite of associated life history traits, exemplified by the ''fast Á/slow continuum'' in mammals. Across the parasitoid Hymenoptera however, a major axis of life history variation is the development mode of the larva (koinobiosis versus idiobiosis), and body size and clutch size do not seem to form clear associations with this major axis. Here we use a large comparative data set and the latest phylogenetic information to explore hypotheses that might explain the variation in body size and clutch size across species in parasitoids. We find evidence for three novel evolutionary correlations: changes in the stage of host attacked by the parasitoid (i.e. egg, larva, pupa) significantly predict changes in both body size and clutch size, whilst in gregarious species changes to higher latitudes are associated with reduced clutch size. We also find a number of hypothesized cross-species (phenotypic) associations that, however, we cannot demonstrate are the result of evolutionary correlations: large bodied species in our data tend to lay small clutches; koinobionts are larger than idiobionts attacking the same host stage; tropical species are smaller than temperate species (Bergmann's rule). Our results provide support for theoretical models of trait evolution in parasitoids, whilst the associations between latitude and life history may help explain why species richness in the family Ichneumonidae peaks at intermediate latitudes. Our results also show the continuing value of phylogenetically-based comparative analyses and demonstrate that recent work on parasitoid phylogenetics has produced significant benefits for our understanding of life history evolution.
The extent to which behavioural choices reflect fine-tuned evolutionary adaptation remains an ope... more 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 Ôgood quality plantsÕ 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.
The sex allocation strategy of the parasitoid Laelius pedatus (Hymenoptera: Bethylidae) on differ... more The sex allocation strategy of the parasitoid Laelius pedatus (Hymenoptera: Bethylidae) on differentsized hosts was investigated. The wasp lays from one to five eggs, and clutch size increases with host size. On the smallest hosts, single male eggs are laid, while on slightly larger hosts single female eggs are laid. On still larger hosts, gregarious clutches are laid which nearly always consist of a single male and one or more female eggs. The sex ratio strategy of the wasp appears to be influenced by a combination of local mate competition and conditional sex expression based on host quality.
Parasitoid wasps exhibit a stark dichotomy in larval behavior and developmental mode. In gregario... more Parasitoid wasps exhibit a stark dichotomy in larval behavior and developmental mode. In gregarious species, siblings developing together tolerate each other; hence more than one individual can successfully complete development. In contrast, solitary species have intolerant larvae that will engage in siblicide, leading to only one individual successfully completing development. Previous theoretical and empirical work has suggested that females from species with intolerant larvae should reduce their relative investment in reproduction. We tested this prediction by measuring investment in survival and reproduction in a pair of sister species from the genus Aphaereta (Hymenoptera: Braconidae). With increasing body size, divergent patterns of investment exist in the two species. Females of the solitary A. genevensis allocate additional resources almost exclusively toward greater fat reserves, resulting in enhanced longevity. Females of the gregarious A. pallipes invest relatively more in reproduction and hence have lower fat reserves, reduced longevity, and greater egg loads than A. genevensis. These differences reflect a trend toward greater investment in survival relative to reproduction in the solitary species, as predicted. We discuss the implications of these findings for the development of sibling rivalry and life-history theory.
Proceedings of The Royal Society B: Biological Sciences, Mar 7, 1998
Data are assembled on the clutch-size strategies adopted by extant species of parasitoid wasp. Th... more Data are assembled on the clutch-size strategies adopted by extant species of parasitoid wasp. These data are used to reconstruct the history of clutch-size evolution in the group using a series of plausible evolutionary assumptions. Extant families are either entirely solitary, both solitary and gregarious, or else clutch size is unknown. Parsimony analysis suggests that the ancestors of most families were solitary, a result which is robust to di¡erent phylogenetic relationships and likely data inadequacies. This implies that solitariness was ubiquitous throughout the initial radiation of the group, and that transitions to gregariousness have subsequently occurred a minimum of 43 times in several, but not all lineages. Current data suggest that species-rich and small-bodied lineages are more likely to have evolved gregariousness, and contain more species with small gregarious brood sizes. I discuss the implications of these data for clutchsize theory.
Deep time is geologic time, extending to the origin of the planet. For biologists in search of an... more Deep time is geologic time, extending to the origin of the planet. For biologists in search of an understanding of extinction, the relevant portion of deep time is that in which life has existed on the planet— about the last 4 billion years (Cowen, 2000). Extinctions are first recorded when the fossil record is robust enough to offer insights into the arrival and disappearance of groups of organisms (Benton and Harper, 2009). Extinctions in deep time can therefore be identified only over about the last 600 million years, an interval of time dominated by the Phanerozoic eon (540 million years ago to present).
Previously, theoretical and empirical studies suggested that parasitoids developing in small mult... more Previously, theoretical and empirical studies suggested that parasitoids developing in small multiple-egg broods would evolve siblicidal behaviour, making such brood sizes rare and single-egg broods an evolutionary absorbing state. Recent evidence, however, suggests that small gregarious broods are relatively stable in many parasitoid taxa, and that gregarious development has evolved many times from solitary development. This suggests that new research is needed to assess how nonsiblicidal behaviour can spread and become stable. We discuss some potentially rewarding possibilities.
Biological control efforts against the shore fly Scatella tenuicosta Collin, a pest of commercial... more Biological control efforts against the shore fly Scatella tenuicosta Collin, a pest of commercial glasshouses, have had limited success. The ability of one of its parasitoids, Aphaereta debilitata Morley, to control shore fly populations was investigated on lettuce crops within six experimental glasshouse units, over 26 weeks. The six shore fly populations, either with or without a single release of 150
bioRxiv (Cold Spring Harbor Laboratory), Jul 8, 2019
1. Insect abundance changes are well-established in some datasets, but far less is known about ho... more 1. Insect abundance changes are well-established in some datasets, but far less is known about how this translates into biomass changes. 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 for moths. This requires estimation of the body mass of moths sampled over time, but such data do not currently exist. 2. We collected empirical data in 2018 on the forewing length and dry mass of 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). We tested the relationships between biomass, abundance and species richness of samples of moths for our 2018 samples, and over a 16-year period using long-term historical moth data (with model-estimated biomass) from a single site. 3. Modelled biomass was positively correlated with measured biomass of moth species (R 2 = 0.910) and mixed-species samples of moths (R 2 = 0.915), showing that it is possible to predict biomass accurately. Biomass correlated with moth abundance and species richness in our 2018 data and in the historical dataset, revealing biomass declined by 65.9 % over a 16-year period. 4. By allowing biomass to be estimated for historical moth abundance datasets, our approach creates opportunities to investigate trends and drivers of insect biomass change over long timescales and broad geographic regions.
1. Several authors have proposed that inter-speci®c variation in parasitoid life histories can be... more 1. Several authors have proposed that inter-speci®c variation in parasitoid life histories can be classi®ed according to a dichotomy of development modes: ectoparasitoids and idiobionts with one suite of traits, and endoparasitoids and koinobionts with an opposing set of traits. 2. The factual evidence for such a dichotomy is presently scant. Here, 10 predictions of the dichotomous hypothesis are assessed using life history data from 474 species of parasitoid Hymenoptera. 3. A degree of support for the dichotomy is found. As predicted, koinobiosis is associated with endoparasitism, and idiobiosis with ectoparasitism. Endoparasitism and/or koinobiosis are also associated with a shorter adult lifespan, a shorter window for parasitism, smaller eggs, a longer pre-adult lifespan and, in larval parasitoids, a greater oviposition rate and fecundity than ectoparasitism/idiobiosis. 4. However, several predictions are not upheld by the data. No signi®cant relationship is found between development mode and either body size, the degree of host concealment or the stage of host attacked. Some trends are only found amongst larval parasitoids, and others do not hold for both endoparasitism and koinobiosis. 5. We conclude that there is at least some merit to the dichotomous hypothesis, though the most extensive depictions go beyond the present data. As a step towards formulating the dichotomy in a more rigid theoretical base, we discuss the selective pressures and constraints that are likely to account for the observed trends.
Bethylid wasps are a medium sized family o f parasitic Hymenoptera, with biological control poten... more Bethylid wasps are a medium sized family o f parasitic Hymenoptera, with biological control potential, which have recently proved excellent model systems for testing evolutionary and life history theory. We report observations on a species of Laelius from The Netherlands. The species is morphologically indistinguishable from Laelius pedatus, previously reported only from the N ew World. Reciprocal crosses between the Dutch wasps and L. pedatus from Madison, Wisconsin, U SA confirmed that the Dutch population belongs to L. pedatus. We compared the life history o f the Dutch wasps with those from Madison by rearing them on Trogoderma glabrum, but found no significant differences. The Dutch wasps successfully parasitize Trogoderma angustum, an invasive museum and domestic pest found in situ, but suffer high developmental mortality on T. glabrum. Wasp egg size was positively correlated with the size o f ovipositing female, which was also negatively correlated with the developmental mortality of offspring. Larger wasps also carried more mature eggs. Time taken to lay the clutch increased with the size o f the eventual clutch laid and was longer in unmated than mated females. When some wasps died before completing development, surviving members of the brood grew to a larger size and took longer to complete development. The number o f males per brood increased with previous oviposition experience, an indication o f sperm depletion through life. We discuss the implications o f these trends for parasitoid life history theory.
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Papers by Peter Mayhew