Short-lived Adults Research Articles

Sex-linked differences in semiochemical-mediated movement by Trogoderma variabile Ballion and Trogoderma inclusum LeConte (Coleoptera: Dermestidae) after exposure to long-lasting insecticide-incorporated netting

Stored product insects are highly mobile and present in the landscape and can disperse by tracking odors of food and pheromones. A novel preventative integrated pest management (IPM) tactic to intercept dispersing insects of durable commodities (e.g., packaged goods, flour, bulk commodities), is a long-lasting insecticide-incorporated netting (LLIN) containing 0.4% deltamethrin. However, it is unknown how exposure to the deltamethrin-based LLIN (LLIN hereafter) may affect olfaction and orientation to important semiochemicals by stored product insects. In this study, our aims were to evaluate whether exposure to LLIN affected male and female (or mixed sex) populations of Trogoderma variabile and T. inclusum movement in the presence of important semiochemicals, including food kairomones and pheromones, including the major sex pheromone for Trogoderma spp. (e.g., (Z)-14-methyl-8-hexedecenal). We evaluated this with a video-tracking protocol and confirmed volatile emissions with headspace collection coupled with gas chromatography and mass spectrometry (GC/MS). Disruption in movement in this study is taken to mean a significant upregulation or downregulation in response compared to our netting without active ingredient (control). Distance moved increased 4–6-fold in T. variabile after exposure to LLIN compared to control netting, while it was reduced by a third to a half in T. inclusum. Overall, out of 40 possible olfactory and taxis patterns which could be disrupted, exposure to LLIN interrupted 68–73% of these in T. inclusum and T. variabile, respectively, compared to control netting-exposed individuals. Pheromonal stimuli were more important for males, but food and pheromones were equally important for females. Our research suggests the use of LLIN may enhance the effectiveness of other behaviorally-based management strategies when used as part of a comprehensive IPM program for these short-lived adults.

An independent origin of an annual life cycle in a North American killifish species

Abstract An annual life cycle is characterized by short-lived adults that exploit seasonally productive but temporary habitats, paired with a hardy embryo stage that survives unfavourable environmental conditions, such as winter or the dry season. This life cycle is rare amongst vertebrates but has evolved independently several times in African and South American killifishes adapted to life in seasonally ephemeral aquatic pools. A single species of North American annual killifish, with a limited geographical distribution in Mexico, also exhibits this seasonal life cycle. This enigmatic species, Millerichthys robustus, is geographically separated from the nearest South American annual killifish species by >2000 km. Millerichthys robustus exhibits morphological features that have led to several competing phylogenetic hypotheses. To date, its phylogenetic relationships are unclear because no molecular data have been available. Here, we sequence the mitochondrial genome of Millerichthys robustus and generate a molecular phylogeny of killifishes that includes this species. Our results indicate that, rather than being most closely related to South American annual killifishes, this species is sister to two non-annual killifish species from Cuba (Rivulus cylindraceus and Rivulus berovidesi). Ancestral state reconstruction strongly supports an independent origin of an annual life cycle and embryonic diapause in Millerichthys robustus.

Effects of population density on adult morphology and life-history traits of female Mediterranean flour moth, Ephestia kuehniella (Lepidoptera: Pyralidae)

Intraspecific competition and food shortage due to high population density during early life can have a profound effect on adult fitness. Organisms often mitigate negative effects of high population density by adjusting resource allocation to adult morphological and life-history traits. In Lepidoptera with short-lived adults that do not feed, it is predicted that females developed from dense larval aggregations invest more in reproduction and traits linked to offspring survival. Here, we investigated the effects of larval population density on adult morphology and life-history traits in the female Mediterranean flour moth, Ephestia kuehniella by raising larvae at a range of population densities. Adults from high population density (16 larvae per g of food) had smaller head, thorax, and forewing compared to other densities. The allometric slope of forewing length with body mass did not differ among population densities, indicating no changes in adult wing morphology at high population density. However, we found that females emerged from larvae at high population density had bigger abdomens relative to body mass, indicating resource investment in reproduction, probably to mitigate the negative effects of crowding on egg production. Ovipositor length did not differ among population densities, indicating conservation of resources to structures with egg-laying function that affect offspring survival. Taken together, these results suggest that female E. kuehniella responding to high larval population density invest relatively more in reproduction, a life-history strategy that could alleviate negative effects of population density on fitness. This study also highlights the importance of a species' reproductive strategy in its adaptive response to environmental conditions, which is relevant to many capital breeders dependent on larval resources for reproduction.

Developmental and sexual divergence in the olfactory system of the marine insect Clunio marinus

An animal’s fitness strongly depends on successful feeding, avoidance of predators and reproduction. All of these behaviours commonly involve chemosensation. As a consequence, when species’ ecological niches and life histories differ, their chemosensory abilities need to be adapted accordingly. The intertidal insect Clunio marinus (Diptera: Chironomidae) has tuned its olfactory system to two highly divergent niches. The long-lived larvae forage in a marine environment. During the few hours of terrestrial adult life, males have to find the female pupae floating on the water surface, free the cryptic females from their pupal skin, copulate and carry the females to the oviposition sites. In order to explore the possibility for divergent olfactory adaptations within the same species, we investigated the chemosensory system of C. marinus larvae, adult males and adult females at the morphological and molecular level. The larvae have a well-developed olfactory system, but olfactory gene expression only partially overlaps with that of adults, likely reflecting their marine vs. terrestrial lifestyles. The olfactory system of the short-lived adults is simple, displaying no glomeruli in the antennal lobes. There is strong sexual dimorphism, the female olfactory system being particularly reduced in terms of number of antennal annuli and sensilla, olfactory brain centre size and gene expression. We found hints for a pheromone detection system in males, including large trichoid sensilla and expression of specific olfactory receptors and odorant binding proteins. Taken together, this makes C. marinus an excellent model to study within-species evolution and adaptation of chemosensory systems.

Seasonality and weather conditions jointly drive flight activity patterns of aquatic and terrestrial chironomids

BackgroundChironomids, a major invertebrate taxon in many standing freshwaters, rely on adult flight to reach new suitable sites, yet the impact of weather conditions on their flight activity is little understood. We investigated diel and seasonal flight activity patterns of aquatic and terrestrial chironomids in a reclaimed sandpit area and analysed how weather conditions and seasonality influenced their total abundance and species composition.ResultsAir temperature, relative humidity, wind speed, and air pressure significantly affected total flight activity of both groups, but not in the same way. We identified an intermediate temperature and humidity optimum for the flight activity of terrestrial chironomids, which contrasted with weaker, timescale-dependent relationships in aquatic species. Flight activity of both groups further declined with wind speed and increased with air pressure. Observed flight patterns also varied in time on both daily and seasonal scale. Flight activity of both groups peaked in the evenings after accounting for weather conditions but, surprisingly, aquatic and terrestrial chironomids used partly alternating time windows for dispersal during the season. This may be driven by different seasonal trends of key environmental variables in larval habitats and hence implies that species phenologies and conditions experienced by chironomid larvae (and probably other aquatic insects with short-lived adults) influence adult flight patterns more than weather conditions.ConclusionsOur results provide detailed insights into the drivers of chironomid flight activity and highlight the methodological challenges arising from the inherent collinearity of weather characteristics and their diurnal and seasonal cycles.

Dietary protein and lifespan across the metamorphic boundary: protein-restricted larvae develop into short-lived adults.

Restriction of nutrients in the adult diet extends lifespan across a diverse range of species, but less is known about the long-term effects of developmental dietary restriction. In particular, it is not known whether adult lifespan is influenced by developmental caloric restriction or macronutrient balance. We used the nutritional geometry approach to independently manipulate protein and carbohydrate contents of the larval diet in the neriid fly, Telostylinus angusticollis, and measured adult lifespan. We found that adult male and female lifespan was shortest when larvae were fed a protein restricted diet. Thus, protein restriction in the larval diet has the opposite effect of protein restriction in the adult diet (which prolongs life in this species and across a wide range of taxa). Adult lifespan was unaffected by larval dietary carbohydrate. These patterns persisted after controlling for larval diet effects on adult body size. We propose that larval and adult protein sources are used for distinct metabolic tasks: during development, dietary protein is used to build a durable soma that enhances adult lifespan, although excessive protein consumption partially reverses this effect.

Sex- and tissue-specific profiles of chemosensory gene expression in a herbivorous gall-inducing fly (Diptera: Cecidomyiidae).

BackgroundThe chemical senses of insects mediate behaviors that are closely linked to survival and reproduction. The order Diptera contains two model organisms, the vinegar fly Drosophila melanogaster and the mosquito Anopheles gambiae, whose chemosensory genes have been extensively studied. Representing a third dipteran lineage with an interesting phylogenetic position, and being ecologically distinct by feeding on plants, the Hessian fly (Mayetiola destructor Say, Diptera: Cecidomyiidae) genome sequence has recently become available. Among plant-feeding insects, the Hessian fly is unusual in ‘reprogramming’ the plant to create a superior food and in being the target of plant resistance genes, a feature shared by plant pathogens. Chemoreception is essential for reproductive success, including detection of sex pheromone and plant-produced chemicals by males and females, respectively.ResultsWe identified genes encoding 122 odorant receptors (OR), 28 gustatory receptors (GR), 39 ionotropic receptors (IR), 32 odorant binding proteins, and 7 sensory neuron membrane proteins in the Hessian fly genome. We then mapped Illumina-sequenced transcriptome reads to the genome to explore gene expression in male and female antennae and terminal abdominal segments. Our results reveal that a large number of chemosensory genes have up-regulated expression in the antennae, and the expression is in many cases sex-specific. Sex-specific expression is particularly evident among the Or genes, consistent with the sex-divergent olfactory-mediated behaviors of the adults. In addition, the large number of Ors in the genome but the reduced set of Grs and divergent Irs suggest that the short-lived adults rely more on long-range olfaction than on short-range gustation. We also report up-regulated expression of some genes from all chemosensory gene families in the terminal segments of the abdomen, which play important roles in reproduction.ConclusionsWe show that a large number of the chemosensory genes in the Hessian fly genome have sex- and tissue-specific expression profiles. Our findings provide the first insights into the molecular basis of chemoreception in plant-feeding flies, representing an important advance toward a more complete understanding of olfaction in Diptera and its links to ecological specialization.

Immature Insects: Ecological Roles of Mobility

Immature insects' adaptations for finding the highest quality food and optimal environmental conditions are critical to maximizing a species' success. Optimal food and environmental conditions during immature development increase the insects' survival and shorten their development time; these conditions also result in earlier reproduction and more rapid growth of the insect population. Immature-stage mobility is important in finding suitable food and environment, building shelters, thermoregulating behavior, and evading, escaping, or defending against natural enemies. The immature stages can move distances ranging from a few centimeters to a few hundred meters; whereas adults that can fly can move distances of a few, hundreds, or even thousands of kilometers. Mobility gives immature insects greater access to available food. Neonate larvae often must move large distances to find their first meal or they perish. Air currents, stream flow, or phoresy can carry them farther than walking. Feeding habits of subsequent instars may change as they grow, and larvae may commute between feeding and resting (shelter) sites. An immature insect may feed at many locations during its development, and mature larvae wander in search of a pupation site. Larvae of >361 insect species in 59 families and 5 orders leave their feeding sites to find a pupation site. Among species with nonfeeding, short-lived adults, the immature stages may accumulate food reserves needed for egg production in the adult stage. Larvae select a safe site before entering larval or pupal diapause for overwintering or summer aestivation, and some larvae may remain mobile during diapause. Active pupae or nymphs may increase the chance of successful adult eclosion. In this article, we review the many important ecological roles of immature mobility.

Transcript profiles of long- and short-lived adults implicate protein synthesis in evolved differences in ageing in the nematode Strongyloides ratti

The nematode Strongyloides ratti shows remarkable phenotypic plasticity in ageing, with parasitic adults living at least 80-times longer than free-living adults. Given that long- and short-lived adults are genetically identical, this plasticity is likely to be due to differences in gene expression. To try and understand how this inter-morph difference in longevity evolved, we compared gene expression in long- and short-lived adults. DNA microarray analysis of long- and short-lived adults identified 32 genes that were up-regulated in long-lived adults, and 96 genes up-regulated in short-lived adults. Strikingly, 38.5% of the genes expressed more in the short-lived morph are predicted to encode ribosomal proteins, compared with only 9% in the long-lived morph. Among the 32 longevity-associated genes there was very little enrichment of genes linked to cellular maintenance. Overall, we have therefore observed a negative correlation between expression of ribosomal protein genes and longevity in S. ratti. Interestingly, engineered reduction of expression of ribosomal protein genes increases lifespan in the free-living nematode Caenorhabditis elegans. Our study therefore suggests that differences in levels of protein synthesis could contribute to evolved differences in animal longevity.

Stage-related variation in rapid cold hardening as a test of the environmental predictability hypothesis

The environmental predictability (EP) hypothesis proposes that rapid cold hardening (RCH) might be common in temperate species incapable of surviving freezing events and which also dwell in unpredictable environments. The kelp fly Paractora dreuxi serves as a useful model organism to test this prediction at an intra-specific level because larvae and adults show different responses to low temperature despite occupying a similar unpredictable thermal environment. Here, using acclimation temperatures, which simulated seasonal temperature variation, we find little evidence for RCH in the freeze-intolerant adults but a limited RCH response in freeze-tolerant larvae. In the relatively short-lived adults, survival of −11 °C generally did not improve after 2 h pre-treatments at −4, −2, 0, 10, 20 or 25 °C either in summer- (10 °C) or winter (0 °C)-acclimated individuals. By contrast, survival of summer-acclimated larvae to −7.6 °C was significantly improved by ∼37% and 30% with −2 and 0 °C pre-treatments, respectively. The finding that summer-acclimated larvae showed RCH whereas this was not the case in the winter-acclimated larvae partially supports the predictions of the EP hypothesis. However, the EP hypothesis also predicts that the adults should have demonstrated an RCH response, yet they did not do so. Rather, it seems likely that they avoid stressful environments by behavioural thermoregulation. Differences in responses among the adults and larvae are therefore to some extent predictable from differences in their feeding requirements and behaviour. These results show that further studies of RCH should take into account the way in which differences among life stages influence the interaction between phenotypic plasticity and environmental variability and predictability.

RNAi-mediated suppression of the mitochondrial iron chaperone, frataxin, in Drosophila

The mitochondrial iron chaperone, frataxin, plays a critical role in cellular iron homeostasis and the synthesis and regeneration of Fe-S centers. Genetic insufficiency for frataxin is associated with Friedreich's Ataxia in humans and confers loss of function of Fe-containing proteins including components of the respiratory chain and mitochondrial and cytosolic aconitases. Here, we report the use of RNA-interference (RNAi) to suppress frataxin in the multicellular eukaryote, Drosophila. Phenotypically, suppression of the Drosophila frataxin homologue (dfh) confers distinct phenotypes in larvae and adults, leading to giant long-lived larvae and to conditional short-lived adults. Deficiency of the DFH protein results in diminished activities of numerous heme- and iron-sulfur-containing enzymes, loss of intracellular iron homeostasis and increased susceptibility to iron toxicity. In parallel with the differential larval and adult phenotypes, our results indicate that dfh silencing differentially dysregulates ferritin expression in adults but not in larvae. Moreover, silencing of dfh in the peripheral nervous system, a specific focus of Friedreich's pathology, permits normal larval development but imposes a marked reduction in adult lifespan. In contrast, dfh silencing in motorneurons has no deleterious effect in either larvae or adults. Finally, overexpression of Sod1, Sod2 or Cat does not suppress the failure of DFH-deficient animals to successfully complete eclosion, suggesting a minimal role of oxidative stress in this phenotype. The robust developmental, biochemical and tissue-specific phenotypes conferred by DFH deficiency in Drosophila provide a platform for identifying genetic, nutritional and environmental factors, which ameliorate the symptoms arising from frataxin deficiency.

Extended alloparental care in the almost solitary bee Exoneurella eremophila (Hymenoptera: Apidae)

The possibility of extending brood care via the overlapping presence of relatively short lived adults could generate advantages that may have been among the selective forces at the origin of eusociality. In this paper we provide evidence for extended brood care through sib-rearing in the arid-zone allodapine bee, Exoneurella eremophila. Solitary females of the overwintered generation generally die before all their offspring have become independent. In a relatively high proportion of nests, a newly eclosed female invests in her siblings while producing her own offspring in the maternal nest. The sex ratio of the first offspring produced by the overwintered female is highly female biased, but the overall sex ratio of the brood is unbiased. This finding supports the prediction of Bull's 'insurance by protogyny' model of a female bias in the first-produced offspring as a strategy by the mother to ensure extended brood care.

A new family of froghoppers from the American tropics (Hemiptera: Cercopoidea: Epipygidae)

ABSTRACT Froghoppers (Cercopoidea) are divided into three families: spittlebugs or Cercopidae, which are efficient spittle-producers; Clastopteridae (including subfamily Machaerotinae, new status), inefficient spittle-producers and tube-dwellers; and the new-world tropical Epipygidae, a new family known only from small numbers of adult specimens. Epipygidae are probably single-brooded, with shortlived adults that appear to rely mainly on stored body fat as an energy source. Unlike the related spittlebugs they probably lay exposed eggs and have free-living nymphs. The new genera Epipyga (typespecies Eicissus tenuifasciatus Jacobi) and Erugissa (type-species Erugissa pachitea sp. nov.) are described and Epipyga cribrata (Lethierry), a new combination from Aphrophora, plus Eicissus decipiens Fowler and twenty-seven undescribed species are included in the family.

Dormancy in Invertebrates

The ability to survive in a dormant state is a widespread, yet unevenly distributed feature among invertebrates. Organisms belonging to classes and phyla that include fresh-water or terrestrial representatives are more likely to possess a dormant stage than those in groups that are exclusively marine. Moreover, within taxa where has evolved, it is more common among fresh-water and terrestrial species than in marine species. This correlation between and habitat across 29 free-living invertebrate phyla raises the question of cause and effect. Are dormant stages more commnon in fresh-water and terrestrial habitats because there is greater selection for in those environments, or is a prerequisite for the successful invasion of non-marine systems? The mechanism of varies among species and ranges from a specialized diapausing embryo to a quiescent adult. Dormancy has most likely arisen multiple times in invertebrate life histories, both within and between phyla. Although may facilitate the invasion of fresh-water and terrestrial habitats, it is not always a requirement: many non-marine species do not exhibit dormancy. Additional key words: diapause, quiescence, life history, fresh-water, marine All natural environments vary, and organisms may occasionally experience conditions that are limiting for growth, survival, or reproduction. The form and nature of this variability differ among habitats, however, and this has led to the evolution of a wide array of life histories (reviewed by Roff 1992; Stearns 1992). For example, some species are iteroparous and offset the negative effects of temporal variation with long-lived adults that reproduce multiple times (Murphy 1968; Goodman 1984). Alternatively, other organisms avoid deleterious environmental conditions with reliable migration (Dingle 1978; Levin et al. 1984; Wiener & Tuljapurkar 1994). However, many species without either of these traits persist in variable environments. Often, these taxa inhabit relatively isolated, transient systems that can support life only for a fraction of the year (e.g., arctic tundra, deserts, temporary ponds). When organisms cannot migrate away from declining environmental conditions, and active adults cannot survive, the only viable option is persistence through dormancy. Dormancy has evolved in numerous bacterial, fungal, protist, plant, and animal species, but is completely unknown in many groups. Although all forms result a Present address: Illinois Natural History Survey, Champaign, IL 61820, USA. Voice: 217-244-2139. Fax: 217333-6294. E-mail: caceres@mail.inhs.uiuc.edu in some type of metabolic and/or developmental depression, the term dormancy actually encompasses a wide range of physiological states (see Hand 1991). Therefore, the form and duration of the dormant state vary widely among taxa. Whereas some species remain dormant only as long as conditions are unfavorable, others remain dormant for time periods much longer than the unfavorable environmental conditions, in :some cases for a century or more (Harper & White 1974; Henis 1987; Hairston et al. 1995; Caiceres 1997). ]Dormancy that extends beyond the duration of the environmental hardship introduces potential costs and benefits. When is not terminated upon the return of favorable conditions, there is the potential cost of lost reproduction. However, when the dormant prcpagules from a single cohort continue to introduce recruits into the active population for several years, populations of short-lived adults can sample different environments much in the same way as a long-lived iteroparous species (Seger & Brockmann 1987). Thus, overlapping generations are established in populations that might otherwise consist of discrete cohorts (Templeton & Levin 1979). ]In theory, the evolution of prolonged should be an alternative to either iteroparity or dispersal (Venable & Lawlor 1980; Levin et al. 1984; Rees 1994). In fact, these alternative life histories have been found in some natural systems. Rees (1993), in This content downloaded from 157.55.39.127 on Wed, 29 Jun 2016 04:32:53 UTC All use subject to http://about.jstor.org/terms

Temperature-Sensitive Development: Consequences for Local Persistence of Two Subtropical Fig Wasp Species

-Larval development of the species-specific pollinators (Agaonidae, Hymenoptera) of the two native Florida fig species is markedly temperature-sensitive. Census data from a site near Miami indicate that Pegoscapus assuetus (the pollinator of Ficus citrifolia) and Pegoscapus jimenezi (the pollinator of Ficus aurea) take 7-8% longer to develop for each 1 C decrease in ambient temperature. However, development does not slow sufficiently to permit the wasps to remain within their sheltered larval habitat (the fig inflorescence) throughout winter, a season in which the short-lived adults have little chance of finding an oviposition site. The difficulty of wasp persistence through winter is probably a major factor limiting most fig-pollinator mutualisms to the tropics. The ability of a few species to persist at the northern limits of some subtropical regions, such as in S Florida, remains unexplained.

Periodicity in Mate Attraction and Flight Activity of Three Species of Caddisflies (Trichoptera)

Diel periodicities of mate attraction and flight activity were examined for three caddisfly species (Insecta:Trichoptera) that use female sex pheromones to attract conspecific males: Dicosmoecus gilvipes (Hagen) (Limnephilidae), Gumaga nigricula (McL.) (Sericostomatidae), and Gumaga griseola (McL.). Live females of D. gilvipes attracted males during the night, with 58% of the males being captured in the first hour after sunset. Live females of G. griseola attracted 97% of the males during the hour before sunrise whereas live females of G. nigricula attracted 85% of the males 2-4 h after sunrise. For all three species, the periodicity of male response to female pheromone was the same as the periodicity of male response to live females. In laboratory chambers, male and female D. gilvipes flew during the mate attraction period but generally not at other times. Male flight for G. nigricula and G. griseola was generally most intense during periods of mate attraction, and was reduced during non-attraction periods. In contrast, females of both Gumaga species were relatively sedentary during periods of mate attraction. The presence of circadian rhythms that govern the periodicity of flight was demonstrated for all taxa and sexes except females of D. gilvipes. Light intensity and air temperature influenced the amount of flight activity but not flight periodicity. The temporally brief and coordinated activities of these short-lived adults may serve to conserve metabolic resources, contribute to their reproductive success, and maintain reproductive isolation.

POPULATION SYNCHRONY IN MAYFLIES: A PREDATOR SATIATION HYPOTHESIS.

The larvae of mayflies (Order: Ephemeroptera) inhabit most permanent freshwater environments (rivers, lakes, ponds). The duration of the mayfly life cycle varies from a few weeks to several years depending on the response of each species to regional climate and nutrition (Needham et al., 1935). Most of the mayfly life cycle is spent in either the egg or larval stage because almost none of the adults feed and, depending on the species, live only about 10 min to 48 h before reproduction and death. Adults of many species appear in flight in large numbers during a brief period each year and form vast mating swarms over the water surface. Both the size and periodicity of mayfly swarms have been conspicuous enough to stimulate detailed descriptions by early naturalists (see Needham et al., 1935 for review) as well as more recent speculation concerning the ecological and evolutionary significance of swarm periodicity (Corbet, 1964; Edmunds and Edmunds, 1980). Population synchronization in aquatic insects, especially mayflies, refers to a tendency for the adult reproductive stage of individuals in a given population to be active in the environment during a short, well defined period of the year (i.e., seasonal synchronization within a time frame >24 h but usually less than 2-4 wk) and/or the day (i.e., time frame <24 h and usually about 1-2 h in duration). For our purpose here, each 24-h period represents a unit of observation and the sum of such units describes the emergence period for each species under consideration. It has been suggested that the adaptive value of adult synchronization for an insect species resides largely with increasing the probability of finding a mate (Corbet, 1964). If so, synchronization should be developed best in species having short-lived adults that are spatially dispersed. This hypothesis is difficult to test because spatial dispersion cannot be adequately determined. In addition, no one has demonstrated for any aquatic species that individuals emerging very early or late in the emergence period fail to mate successfully. Here we argue that mating success is unlikely to have been the only factor selecting for adult synchronization in mayflies. We hypothesize that predator provides a better conceptual framework for assessing adult emergence patterns in mayflies and perhaps other aquatic insects. satiation was used initially to describe the interaction between periodical cicadas (Insecta: Homoptera) and their predators (see Lloyd and Dybas, 1966 for review). Predator occurs when the quantity of a particular prey item (e.g., cicada) at a given point in time far exceeds the potential number that can be taken by a fixed density of local predators (e.g., birds). The predators are satiated and the remaining prey survive to reproduce providing prey densities remain above the level necessary for satiation. Thus, a predator hypothesis for any predator-prey system predicts an inverse relationship between prey mortality due to predation and prey availability above the level needed to satiate predators as long as the number of predators remains more or less fixed for a given time interval. In this paper we present quantitative data on adult mortality during each day of the adult emergence period for the mayfly Dolania americana Edmunds and Traver to demonstrate how emergence

Nerol-derived volatile signals as a biochemical basis for reproductive isolation between sympatric populations of three species of ant-lions (Neuroptera: Myrmeleontidae)

Larvae of the ant-lions Euroleon nostras, Grocus bore and Myrmeleon formicarius are found in mixed populations in some localities in Sweden. The short-lived adults, which live only for pairing and egg-laying, are sympatric both in space and time. The volatile secretion from thoracic glands of adult males and females of the three species has now been chemically analyzed mainly by gas chromatography and mass spectrometry. Males have large glands, which secrete mainly two compounds in each species. In males of E. nostras, neroloxide (a furanoid monoterpene) and an unidentified monoterpene with a mol wt of 170 are each present at approx. 300 μg per insect. In males of G. bore the secretion is composed of two monoterpenes (5 μg each) with mol. wts of 166 and 170. The structure of the first is directly related to neroloxide whereas the second is identical to the second substance in males of E. nostras. Finally, males of M. formicarius have a volatile secretion composed of nerol (0.5 μg), together with a second monoterpene (mol. wt 168) in about equal amounts. The small gland in females of the three species secrete only one substance (about 0.05 μg/gland) which was identified as neroloxide in all of them. All the substances in the three species are closely related to nerol and the unique combination of two of them in males of each species form a species-specific secretion. It has not yet been studied which behavioural steps the substances are affecting but the chemical species specificity observed only in the males indicate a sex pheromone function.

LIFE HISTORY OF THE FUNGUS GNAT MACROCERA NOBILIS IN AMERICAN CAVES (DIPTERA: MYCETOPHILIDAE)

AbstractThe mycetophilid Macrocera nobilis Johnson, previously known only from forests in New Hampshire and Massachusetts, is here reported from caves in Oklahoma, Missouri, Kentucky, Tennessee, and West Virginia. A study of populations in Oklahoma shows that the short-lived adults mate in cave entrances, but that oviposition, larval development, and pupation occur only in the dark zone of caves. The larvae build extensive webs upon which they travel and which they use to capture insect prey (mostly other Diptera). Reproduction and life cycle development is not seasonal. The larval stage lasts 9 or 10 months, and the pupal stage about 2 weeks.

Comparative radiosensitivity in the class insecta

A “radiosensitivity index” (LT 50/mean longevity) was correlated with the mean longevity and dry weight of 37 insect species (both sexes of 12 species) representing eight orders. Curvilinear regression analysis relating radiosensitivity to mean longevity and mean dry weight indicated that 46·3% of the observed variation could be attributed to longevity and 32·6% to the dry weight of the species. In general, large long-lived adults were more radiosensitive than small short-lived adults. Correlation of the phylogeny of insect orders and order groupings with the radio-sensitivity index was found to be poor. However, when the index was related to longevity, there was a tendency for species comprising the major orders investigated to occur in groups along the predicted curve.