Eye and optic lobe metamorphosis in the sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae)

Nearly nothing is known about the transition that visual brain regions undergo during metamorphosis, except for Drosophila in which larval eyes and the underlying neural structure are strongly reduced. We have studied the larvae of the sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae), which are sophisticated visually oriented predators characterized by six elaborate stemmata on each side of the head and an associated large optic lobe. We used general neurohistological staining and 3D reconstruction to determine how the eyes and optic lobe of T. marmoratus change morphologically during metamorphosis. We find that in third (last) instar larvae, the adult neuropils are already forming de novo dorsally and slightly anteriorly to the larval neuropils, while the latter rapidly degenerate. Larval eyes are eventually reduced to distinct areas with dark pigmentation. This complete reorganization, which may be an evolutionarily conserved trait in holometabolous insects, occurs despite the considerable costs that must apply to such a visually complex animal. Our findings are consistent with the concept that stemmata are homologous to the most posterior ommatidia of hemimetabolous insects, an idea also recently supported by molecular data.     

How to avoid becoming a prey: Predatory encounters between an orb-weaving spider,Araneus pinguis (Karsch) (Araneae: Araneidae) and flying insects

Insects flying into the web of an orb-weaving spiderAraneus pinguis (Karsch) and their avoidance of (pre-hitting process) and escapes from (post-hitting process) the web were examined by direct observation under natural and semi-natural conditions. In the pre-hitting process, mobile insects such as Brachycera, Lepidoptera and Hymenoptera showed a low hitting ratio (number of insects hitting/number of insects flying within 1 m³ space around the web-site) because of active web avoidance and flying activity in layers lower or higher than those in which the webs are usually laid. In contrast, less mobile insects like Heteroptera, Coleoptera and Homoptera showed a high hitting ratio. In the post-hitting process, Brachycera, Lepidoptera and some Nematocera frequently escaped without being detained by the web. Many Orthoptera and Hymenoptera escaped without any sign of detection by the spider. Coleoptera frequently escaped during the spider's attack. Small insects from the Homoptera, Nematocera and Hymenoptera rarely escaped from the web, but were not immediately attacked. Mean escape time of insects was correlated significantly with capture success of the spider. Overall most of the escapes occurred in the early phases of the predation process. This indicates that escapes are unlikely to result in heavy loss of time and energy expenditure due to unsuccessful predation. Escape patterns of insects seem to be related to their mobility.     

Feeding Habits of Two Large Insects from a Desert Stream: Abedus herberti (Hemiptera: Belostomatidae) and Thermonectus marmoratus (Coleoptera: Dytiscidae)

Feeding preference experiments were conducted to determine the feeding habits of Abedus herberti (Heteroptera, Belostomatidae) and Thermonectus marmoratus (Coleoptera, Dytiscidae), two large insects in Sycamore Creek, an intermittent Sonoran desert stream, Arizona, U.S.A. Numbers of live versus dead prey consumed were tested between and across three prey sizes. Five prey species were offered simultaneously (5 live and 5 dead specimens) in each size class. We found that A. herberti preferred live prey of small and medium size, but it chose mainly dead prey in the large size class. These results fitted the model of size-selective predation (Zaret, 1980). Size dependent predators selected prey of increased size, according to their visibility, but only up to where difficulty in handling and probability of escape affect successful consumption. Snails were the most preferred prey of A. herberti. By contrast, T. marmoratus consumed only dead prey of all sizes, but it preferred soft organisms with thin cuticle, such as immature larvae of some mayflies, beetles, dragonflies or fishes.     

Behavior and aquatic plants as factors affecting predation by three species of larval predaceous diving beetles (Coleoptera: Dytiscidae)

Predation among aquatic invertebrate predators can have important effects on patterns of exclusion and coexistence in aquatic habitats, especially if these predators also act as intraguild predators. Such patterns may be explained by variation in predator foraging mode and in the extent and overlap of habitat use. Predaceous diving beetles (Coleoptera: Dytiscidae) are abundant in isolated bodies of water and are effective predators on many aquatic organisms, including other dytiscids. The under-investigated role of hunting behavior and habitat use in altering outcomes of predation under different plant densities may offer insights into patterns of coexistence among larval dytiscids. I performed experiments that quantified behavior of larvae of three common genera of dytiscids that share common prey and then measured predation among genera in the presence or absence of aquatic plants. Behavioral analyses concluded that there were significant differences in foraging modes, with Dytiscus primarily exhibiting sit-and-wait tactics, Graphoderus engaging in active, open water searching, and Rhantus displaying combinations of these behaviors. Predation among larvae was common and occurred when predators were larger than the prey, with no indication of prey preference. Incidence of predation among generic combinations depended on the presence of plants and appeared to be related to behavioral differences among genera. The presence or absence of plants and differences in larval behavior may help to mitigate predation by reducing negative interactions in natural aquatic systems. These results have implications for IGP interactions and may be one of the explanations for the observed richness of this group of predators within aquatic habitats.     

Flood pulses drive the temporal dynamics of assemblages of aquatic insects (Heteroptera and Coleoptera) in a temperate floodplain

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Effects of pond size and consequent predator density on two species of tadpoles

Experimental ponds were used as a model system of habitat patches to study the effect of habitat size on the relative growth performance of tadpoles of Bufo americanus and Pseudacris triseriata, and on colonization by predatory insects. Three pond depths and surface areas were habitat size treatments in a replicated, factorial experiment. Tadpoles of both species were astablished together at a single density and ponds were left open to natural colonization by aquatic insects. Pond area had a significant effect on the multivariate response of P. triseriata larval period, survival, and metamorphic mass. P. triseriata survived better relative to B. americanus in larger ponds. However, increasing pond area led to greater incidence of predacious beetle larvae (Dytiscus, Coleoptera: Dytiscidae). Dytiscus larvae had a significant negative effect on the survival of P. triseriata and led to reduced P. triseriata survival relative to B. americanus in colonized ponds. The results suggest that habitat size can influence community structure by altering the distribution of predation among habitat patches.     

Selective predation by larval Agabus (Coleoptera: Dytiscidae) on mosquitoes: support for conservation-based mosquito suppression in constructed wetlands

1. Wetland insect predators can structure aquatic prey communities via selective predation, but receive considerably less attention than vertebrate predators. We conducted laboratory experiments to test selective predation by two species of larval dytiscid beetles ( Agabus ; Coleoptera: Dytiscidae) and the potential contribution of these beetles to suppression of mosquito populations in constructed wetlands.
2.  Agabus consumed copepods, ostracods and mosquito larvae in no-choice tests. When offered a choice, 76% of all prey consumed were mosquito larvae, indicating selective predation. Subsequent experiments revealed this preference was due to ease of capture of mosquito larvae over alternative prey.
3. Cannibalism and intraguild predation were common within and between species of Agabus , which may reduce the overall impact of the observed selective predation.
4.  Agabus larvae selectively preyed on mosquito larvae over alternative prey, which is not characteristic of some fish used as biological control agents for mosquitoes. Predator exclusion or similar experiments in the field could document how these results translate into a natural setting.
5. The findings of this study suggest developing mosquito suppression strategies focused on conservation of native wetland predators. These strategies are preferable to introducing non-native generalist predators, or applying pesticides.     

Insect Seed Predators in Erythrina falcata (Fabaceae): Identification of Predatory Species and Ecological Consequences of Asynchronous Flowering

Seed predation by insects exerts negative effects on plant reproduction by limiting the supply of seeds and preventing germination. Seed predators of the family Fabaceae are usually generalists, which increases the rate of predation. One strategy to minimize seed predation, developed by plants from temperate regions, is “escape in time,” i.e., flowering before or after the peak of predation. For tropical species, few studies have investigated the strategies used by plants to minimize seed predation. Here, using Erythrina falcata, a tropical species of Fabaceae, we test three main hypotheses: (i) escape in time is a mechanism used by E. falcata to minimize seed predation, (ii) the predators of E. falcata seeds are generalists, and (iii) the biometric variables of the pods can influence seed predation. In order to test these hypotheses, we determined the flowering time of E. falcata, rate of seed predation, the predators insects, and biometric variables of the pods. The analyzed trees were grouped into three classes: “early,” “peak,” and “late” flowering. The average seed predation rates on trees in the early and late classes were 65% and 50%, respectively, and in the peak class, 80%; thus, our first hypothesis can be accepted. Three species of Lepidoptera and two of Coleoptera were found preying on E. falcata seeds. These species were observed to be generalist predators; thus, our second hypothesis can be accepted. The biometric variables of the pods cannot influence seed predation rate. The ecological consequences of asynchronous flowering on plants and insects are discussed.     

Euphorine phylogeny: the evolution of diversity in host-utilization by parasitoid wasps (Hymenoptera: Braconidae)

ABSTRACT.

• 1 New data on the phylogeny of the braconid subfamily Euphorinae supports the hypothesis that parasitism of adult insects by Euphorinae originated during parasitism of Chrysomelidae, a group whose larvae are ecologically coincident with adults.
• 2 Evolution of the habit of attacking the adult stage opened a new adaptive zone; subsequently the Euphorinae have diversified on to a phylogenetically greater variety of hosts than any other braconid subfamily.
• 3 Parasitism of eumastacid grasshoppers evolved from beetle parasitism in the tribe Perilitini.
• 4 The tribe Euphorini shows the greatest diversity of hosts utilized. Most attack Heteroptera; however, Chrysopopthorus diversified on to adult Chrysopidae, Euphoriella on to Psocoptera, and Cryptoxilos on to Scolytidae.
• 5 Parasitism of bark beetles (Scolytidae) has evolved independently in three genera: Cosmophorus, Cryptoxilos and Ropalophorus. This is the most specialized form of beetle parasitism by euphorines, since it involves direct parasitism of concealed hosts.
• 6 Parasitism of adult hymenopterans by the tribe Syntretini may be related to attacking hosts while they are foraging at flowers.
• 7 The pattern of diversification in the Euphorinae indicates several adaptive radiations within host orders, as well as a history of major host-shifts between phylogenetically distantly-related host groups: Coleoptera to Orthoptera; Coleoptera to Hymenoptera; Coleoptera to Heteroptera; Heteroptera to Neuroptera, Psocoptera, and back to Coleoptera. Both the‘host taxonomy’and‘host habitat’hypotheses of host-shifting are supported. Host-shifts have involved hosts occurring in the same micro-habitat and usually having similar feeding habits. This is consistent with current theory of host-location by means of host-produced kairomones and visual cues.

     

Taxonomic review of the genus Copelatus Erichson (Coleoptera: Dytiscidae) in Korea

A taxonomic review of the genus Copelatus Erichson (Coleoptera: Dytiscidae) in Korea is presented. In the present study, five species of Copelatus are recognized from Korea, including one unrecorded species, C. kammuriensis. We provide a key to the Korean species of Copelatus, diagnosis of one unrecorded species, habitus photographs, scanning electron micrographs of the elytron, and illustrations of the aedeagus.     

Study of the Insects Associated with the Floodwater Mosquito Ochlerotatus Albifasciatus (Diptera: Culicidae) and their Possible Predators in Buenos Aires Province,Argentina

Insects associated with the floodwater mosquito Ochlerotatus albifasciatus(Diptera: Culicidae) were studied from intermittent puddles in temperate Argentina in an attempt to detect the main predators. Forty-one taxa occurred in the puddles from spring to fall. Coleoptera and Diptera were dominant and diverse. Ephemeroptera and Odonata were scarce in numbers and species, and Heteroptera occurred in low numbers of species and high abundance of individuals. The main predators of immature O. albifasciatus were detected on the basis of relative abundance (ISA index), ecological dominant groups, and species association (I index). Liodessus sp. and Rhantus signatus signatus(Coleoptera: Dytiscidae) were the most abundant predators in the puddles and Liodessus sp., Lancetes marginatus(Dytiscidae) and Psorophora ciliata(Culicidae) were the most frequent. Liodessus sp. and O. albifasciatus were the best associated species in all seasons. Liodessus sp. was indistinctly associated with all larval instars and pupae, while R. signatus signatus, L. marginatus and Psorophora ciliata were more associated with the pupal stage of the mosquito. Desmopachria concolor(Coleoptera: Dytiscidae), Tropisternus lateralis limbatus and Tropisternus setiger(Coleoptera: Hydrophilidae) were other potential predators inhabiting the puddles, but their relevance was minor.     

Insectivory in free-ranging bearded saki (Chiropotes satanas chiropotes)

Bearded saki are considered frugivores primarily specialized for the predation of immature seeds. I report the first observations of wildC. s. chiropotes actively feeding on immature or non-volant insects in the canopy of upland (“terra firme”) rain forest, in Amazonas, Brazil. During one year of field study I recorded 20 insectivory feeding bouts: 18 times on lepidopteran larvae, 1 time on coleopteran larvae, and 1 time on adult ants.     

Colonization of drying temporary wetlands by Coptotomus loticus (Coleoptera: Dytiscidae): a unique strategy for an aquatic wetland insect

Wetlands Ecology and Management - Predaceous diving beetles (Coleoptera: Dytiscidae) are well-known for their ability to colonize both permanent and temporary aquatic habitats. They often move...     

Diets of adult and nestling starlings (Sturnus vulgaris) in Hawke’s Bay,New Zealand

Abstract

Gizzards were examined from 334 adult and 62 nestling starlings collected in mixed farmland during 1971–72. The birds ate insects, spiders, earthworms, snails, millipedes, centipedes, seeds, and fruits. Starlings ate fewer subterranean animals (7%) than those usually living partially hidden (45%), on the ground (31%), or on vegetation (18%). About half the invertebrates eaten were 2–5 mm long and about a quarter 6–10 mm long. Nestlings tend to be fed significantly larger items than were eaten by adults. The commonest items in adult starlings were Coleoptera adults, Lepidoptera larvae, Hemiptera, and fruits; in nestlings, Coleoptera adults and Diptera adults and larvae were important. Earthworms were found in all the nestlings. More than 50% of adult gizzards contained earthworm chaetae in wetter months, but fewer in drier months. The diet of starlings, despite considerable overlap with the foods eaten by mynas, rooks, and magpies, included somewhat different components and proportions of the food supply. Fruits were found in adults only; most were probably eaten after harvest. Although predation on two major pasture pests—Costelytra zealandica and Wiseana cervinata larvae—was insubstantial, nearly 40% of the total invertebrates eaten by adult starlings were insect pest species.     

First observation of Lethocerus cordofanus (Hemiptera: Belostomatidae) preying on Afronycteris nana (Chiroptera: Vespertilionidae)

Giant water bugs (Hemiptera: Belostomatidae) are key predators in freshwater ecosystems and have been reported to feed on several species of vertebrates, including fishes, amphibians and reptiles. Here, we report the opportunistic predation of an adult female vesper bat (Afronycteris nana) by a giant water bug (Lethocerus cordofanus) in a temporary pond in a rice paddy in Guinea-Bissau, West Africa. To our best knowledge, this is the first instance of natural predation upon a mammal by a giant water bug to be documented in a scientific report.     

Greater impact of host plant species on oviposition of a willow leaf beetle <Emphasis Type="Italic">Plagiodera versicolora</Emphasis> Laicharting (Coleoptera: Chrysomelidae) during the adult stage than in developing larval stage

In some herbivorous insects, such as Coleoptera and aphids, not only the host species of larvae, but also those of adults should be considered as key determinants of potential fecundity because oviposition is affected by the quality of host species during both larval and adult stages. This study examined the relatively greater impact on host species of the larval or adult stage on oviposition of the willow leaf beetle Plagiodera versicolora Laicharting (Coleoptera: Chrysomelidae). We conducted an experiment using a 2 × 2 experimental design, in which either of two different host plant species was fed in larval and adult stages. Females fed on a locally unavailable host Salix eriocarpa in the adult stage did not lay any eggs, but those fed on the locally available host S. babylonica laid 67–75 eggs on average, irrespective of larval host species. Such reproductively inactive females fed S. eriocarpa as an adult host recovered reproductive activity within 3 weeks after changing the host species to S. babylonica. This result indicated that the host species fed in the adult stage had a greater impact on oviposition than in the larval stage.     

Kairomonal range of generalist predators in specialized habitats: responses to multiple phloeophagous species emitting pheromones vs. host odors

We evaluated responses of the predominant predators of pheromone-producing bark beetles (Coleoptera: Scolytidae) to chemical cues associated with other phloeophagous species that colonize the same trees. This study considered the range of chemical signals exploited by a category of predators that may be viewed either as specialists, because they feed almost exclusively within trees killed by bark beetles, or as generalists, because they feed on a diverse fauna of primary and secondary insects within this habitat. It also evaluated one aspect of a broader model of predator-prey coevolution, that proposes altered semiochemistry as a source of partial escape from predators that exploit kairomones. The predators, Thanasimus dubius (F.) (Coleoptera: Cleridae) and Platysoma cylindrica (Paykull) (Coleoptera: Histeridae), were attracted to cues associated with feeding on bark-phloem disks by two scolytids that produce adult pheromones, Ips pini (Say) and Ips grandicollis (Eichhoff). These predators were not attracted to beetles that feed on lower stems or roots and are not known to produce adult pheromones,Dendroctonus valens LeConte, Hylastes porculus Erickson (Coleoptera: Scolytidae), and Hylobius pales (Herbst) (Coleoptera: Curculionidae). The predator Tenebroides collaris (Sturm) (Coleoptera: Trogositidae) was attracted to I. pini and I. grandicollis, and also to D. valens, H. porculus, and H. pales. Ips pini was attracted to conspecifics only, but I. grandicollis was attracted both to its conspecifics and to volatiles associated with feeding lower stem and root insects. Lower stem and root insects were not or only weakly attracted to cues associated with their conspecifics. These results are consistent with a dynamic coevolved interaction between T. dubius and P. cylindrica and Ips spp.     

Complete mitochondrial genome of the seven-spotted lady beetle, Coccinella septempunctata (Coleoptera: Coccinellidae)

The complete mitochondrial genome (mitogenome) of the seven-spotted lady beetle, Coccinella septempunctata (Coleoptera: Coccinellidae), which is one of the best known insects capable of predation, is described with an emphasis on the noteworthy composition of the A+T-rich region. The C. septempunctata genome consists of 2 rRNAs, 22 tRNAs, 13 protein-coding genes, and 1 control region, designated as the A+T-rich region in insects. Along with an unusually long A+T-rich region (4469 bp), the 18,965-bp long C. septempunctata mitogenome was the largest in Coleoptera. The A+T-rich region is composed of a 2214-bp long non-repeat region composed of 80.17% A/T nucleotides and a 2256-bp long repeat region composed of 65.71% A/T nucleotides. The repeat region harbors 32 identical 70-bp long tandem repeats plus one 15-bp long incomplete first repeat. These repeat sequences may possibly have been caused by slipped-strand mispairing and unequal crossing-over events during DNA replication.     

Field observation of foraging behavior by a group of adult diving beetles Agabus (Gaurodytes) bipustulatus preying on an adult Lissotriton boscai

Adult dytiscids prey on a variety of items including other invertebrates but also larger prey such as frogs and fish. Observations of anuran larvae predation are common. However, there have been no reports concerning predation on caudata post‐metamorphosis by dytiscids. Here we describe a predation event by a group of adult diving beetles of the species Agabus (Gaurodytes) bipustulatus (Linnaeus, 1767) on an adult Lissotriton boscai (Lataste in Tourneville, 1879). This report represents the first observation of foraging behavior of adult diving beetles preying on and consuming a living post‐metamorphic newt.     

Responses of Acilius sulcatus (Coleoptera: Dytiscidae) to chemical cues from perch (Perca fluviatilis)

In this study we tested the hypothesis that the presence of chemical stimuli from a hungry predator would initiate anti-predator responses, while stimuli from a satiated predator would not. We used chemical stimuli released from starved perch (Perca fluviatilis) and from satiated perch (predator). As prey we used adult Acilius sulcatus (Coleoptera: Dytiscidae). The reaction of the beetles to different predator conditions was tested during daytime. We also tested the reaction to starved perch during the night. A. sulcatus activity decreased when it was exposed to stimuli released from starved perch during daytime when visibility was poor, due to the presence of artificial vegetation. There was, however, no reaction to satiated perch under the same experimental conditions. These results indicate that A. sulcatus can discriminate between chemical cues from hungry and satiated fish predators. When visibility was good and the concentration of chemical cues was constant, the beetles did not react to starved perch in the daytime, but their activity decreased at night in response to stimuli released from starved perch. Visual as well as chemical cues seem to be important for detecting a potential predator. When visibility is good, beetles seem to rely on visual stimuli, while in darkness they seem to use chemical stimuli to detect the presence of predators. Received: 4 October 1996 / Accepted: 7 February 1997