The influence of larval case design on vulnerability of Limnephilus frijole (Trichoptera) to predation

• 1 We examined the potential selective pressures exerted by different types of predators on morphological prey defences using the case-building larvae of the limnephilid caddisfly, Limnephilus frijole. The predators were a predaceous minnow, Gila pandora, and an aeschnid dragonfly naiad, Oplonaeschna armata.
• 2 The influence of larval case design on vulnerability to predators was evaluated in a series of laboratory experiments. Larval L. frijole were collected from a stream without fish or dragonflies. In the laboratory, larvae still occupying their field-built cases were exposed to the two predators, with which L. frijole co-occurs in other streams. Following 24 h exposure of caddisfly larvae to a specific predator, the pre-trial case length, case strength, case width, and case composition of victims and survivors were compared.
• 3 Principal components analysis (PCA) indicated substantial independent variation for all four case parameters in the study population. The cases of larvae surviving exposure to either dragonfly naiads or fish were significantly stronger and wider than cases of victims of predation. Cases of survivors were also longer and had a greater mineral fraction than those of victims, but differences were either marginally significant or not significant.
• 4 These results demonstrate that specific aspects of case design affect the vulnerability of caddisfly larvae. In addition, predaceous fish and predaceous invertebrates, using different predation techniques, may exert similar selective pressures on these defenses. Case aspects influencing vulnerability in these experiments are broadly consistent with natural variation in case design associated with predator-rich and predator-free habitats for related caddisfly species.

     

Ontogenetic changes in the shelter site of a leaf-folding caterpillar, Vanessa indica

Factors responsible for ontogenetic habitat shifts were examined using larvae of the Indian red admiral butterfly, Vanessa indica (Herbst) (Lepidoptera: Nymphalidae). The larvae of V. indica fold leaves of China ramie, Boehmeria nipononivea Koidz. (Urticaceae), to form shelters that also serve as food. When constructing shelters, old larvae (usually third instar or older) frequently cut trenches at the bases of the leaves, whereas younger larvae do not. This trenching behaviour reduces the force required to fold large ramie leaves. Young larvae used small apical leaves as shelter sites. Once larvae were capable of cutting trenches, they moved proximally on the host plant and used middle leaves that either had completed or were about to complete expansion. Results of bioassays revealed that, for young larvae, apical and middle leaves did not differ in food quality. In contrast, for older larvae, the quality of middle leaves was higher than that of apical leaves. These observations suggest that young larvae decrease the risk of predation during shelter construction by using apical leaves that are relatively easy to fold, and that old larvae employ trenching to decrease the duration of leaf folding and improve growth rate by using middle leaves that are of high quality. Thus, the facilitation of leaf-folding by trenching is considered to reduce the necessity of using apical leaves, and the acquisition of the trenching ability triggers an ontogenetic shift in the selection of larval shelter sites.     

Assessment of trends in predation pressure on insects across temperate forest microhabitats

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Expression of a behaviourally mediated morphology in response to different predators

The risk of predation generally entails alterations in prey behaviour or morphology, but only a few organisms, such as caddisfly larvae, are able to undergo rapid morphological changes mediated by behaviour. Here I explore whether predatory fish (Squalius pyrenaicus) and crayfish (Procambarus clarkii) provoke similar responses from caddisfly larvae (Calamoceras marsupus) in terms of the speed of case construction and the use of different materials differing in their protective value (sticks > leaves; tough leaves > soft leaves). Laboratory experiments demonstrated that C. marsupus larvae were able to recognise both types of predators, and responded to them by constructing a case within hours. Moreover, predation risk motivated the use of more protective materials for case construction when compared to controls. The response to the crayfish was faster than that to the fish, which could be related to differences in the nature and predation efficiency of different predators (i.e. crayfish may be more efficient at predating on leaf litter-dwelling invertebrates than fish, which live in the water column). This study provides novel evidence about the expression of morphological defences mediated by behavioural responses to predation risk, and demonstrates that the speed of case construction and its resulting protection level can vary depending on predator nature.     

Non‐pathogenic aquatic bacteria activate the immune system and increase predation risk in damselfly larvae

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Predation by wasps on lepidopteran larvae in an Ozark forest canopy

ABSTRACT.

• 1 Predation by birds, crawling arthropods (ants, harvestmen, spiders), and social wasps (Vespula) spp. on introduced stocks of Heliothis virescens (Fabricius) larvae was investigated in a oak-hickory forest canopy in northwestern Arkansas (U.S.A.).
• 2 Wasps, Vespula maculifrons (Buysson) and V.squamosa (Drury), removed over 90% of the larvae. Repeated visits to a feeding site by the same marked wasps accounted for removal of either a single larva or all larvae. Larvae pinned (punctured) to artificial leaves were selected over 70% of the time by wasps when compared to attachments that did not puncture larvae; however, unpunctured larvae were taken.
• 3 Crawling arthropods accounted for low levels of predation, and birds did not appear to prey on larvae. Apparently wasps removed larvae rapidly and efficiently, thereby depleting the feeding sites before other predators discovered the larvae.
• 4 Although attaching larvae to artifical hickory leaves provided an easy method for placing larvae into the forest canopy, a lower percentage of larvae were removed from these leaves compared to natural hickory leaves. Moving feeding sites did not influence the number of larvae taken.

     

Reproductive and subsocial behaviour in the ovoviviparous leaf beetle Gonioctena sibirica (Coleoptera: Chrysomelidae)

Abstract.

• 1 In the spring, females of the leaf beetle Gonioctena sibirica deposited larvae on the ventral surface of growing young leaves situated on the apical position of shoots of the willow Salix bakko.
• 2 The parent females remained with the larvae usually on the underside of the basal part of leaves, facing toward the base of shoots. When other arthropods approached, the females temporarily moved towards these intruders, showing aggressive behaviour such as swinging the body or stamping the legs. Many females remained with their larvae until the larvae grew into the final (fourth) instar. No female produced an additional brood in the field.
• 3 Broods from which parent females were experimentally removed suffered higher mortality than those in which females were left intact. Arthropods such as spiders and ants were observed preying on the larvae. In contrast, the survivorship of broods from which females were removed and intruders were excluded with a sticky substance applied to the base of twigs was not different from that of control broods. These results demonstrate that the main mortality factor of offspring is pedestrian arthropod predators and females physically repel the predators.
• 4 Potentially alternative reproductive strategies, such as producing a large number of offspring by iteroparity and/or larger brood(s) with less or no care, seem to be inhibited in G.sibirica by larval dependence on growing young leaves which are temporally limited and by ovoviviparity which may have limited brood size.

     

Predation risk and habitat complexity modify intermediate predator feeding rates and energetic efficiencies in a tri‐trophic system

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Past and Present Risk: Exposure to Predator Chemical Cues Before and after Metamorphosis Influences Juvenile Wood Frog Behavior

Animals are exposed to different predators over their lifespan. This raises the question of whether exposure to predation risk in an early life stage affects the response to predators in subsequent life stages. In this study, we used wood frogs (Rana sylvatica) to test whether exposure to cues indicating predation risk from dragonfly larvae during the wood frog larval stage affected post‐metamorphic activity level and avoidance of garter snake chemical cues. Dragonfly larvae prey upon wood frogs only during the larval stage, whereas garter snakes prey upon wood frogs during both the larval stage and the post‐metamorphic stage. Exposure to predation risk from dragonflies during the larval stage caused post‐metamorphic wood frog juveniles to have greater terrestrial activity than juvenile wood frogs that were not exposed to larval‐stage predation risk from dragonflies. However, exposure to predation risk as larvae did not affect juvenile wood frog responses to chemical cues from garter snakes. Wood frogs exposed as larvae to predation risk from dragonfly larvae avoided garter snake chemical cues to the same extent as wood frog larvae not exposed to predation risk from dragonfly larvae. Our results demonstrate that while some general behaviors exhibit carry‐over effects from earlier life stages, behavioral responses to predators may remain independent of conditions experienced in earlier life stages.     

The effect of invertebrate and vertebrate predators on the foraging movements of Ischnura elegans larvae (Odonata: Zygoptera)

SUMMARY.

• 1 The foraging movements of late instar Ischnura elegans larvae were monitored in laboratory experiments to study the effects of predators on larval feeding behaviour.
• 2 Ischnura larvae are sit-atid-wait, or ambush, foragers, moving occasionally between perches in search of profitable feeding sites. Larval foraging movements, monitored at different densities of Daphnia prey, increased significantly when prey were absent.
• 3 In experiments without prey, larval movement was inhibited by the presence of fish predators, as well as by invertebrate predators (Notonecta glauca), but not by closely related, non-predatory invertebrates (Corixa punctata) or physical disturbance of the water (intermittent air bubbles).
• 4 Further experiments varied Ischnura hunger levels (0–8 days without food) and illumination (light or dark) with and without notonectid predators. Hunger had no consistent effect on penultimate instar behaviour but final instar foraging activity was significantly modified: movements increased after 4 days starvation and decreased again after 8 days. This response was suppressed by the presence of predators. Both larval instars moved significantly less often in the light, even when predators were absent.
• 5 These phenotypically flexible predator-avoidance responses are likely to decrease the risk of predation by both visual and tactile predators. However, predators clearly have an important influence on the feeding niche of Ischnura larvae, and may decrease the overall feeding efficiency, growth rate, and survival of larvae by constraining their movement in search of profitable feeding sites.

     

Increasing conspecific density weakens the ability of intermediate predators to develop induced morphological defences to top predators

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Larval interactions in aphidophagous predators: effectiveness of wax cover as defence shield of Scymnus larvae against predation from syrphids

Small-sized predators in the aphidophagous guild of Aphis gossypii Glover colonies on hibiscus trees in Japan exploit aphids at low prey abundance. Scymnus (Pullus) posticalis Sicard beetles were the first predatory species to attack aphids in the spring, and their larvae co-occurred with larvae of Eupeodes freguens (Matsumura) syrphids in aphid-infested leaves of hibiscus for 3 weeks in absence of large-sized coccinellid predators. Larval interaction between Scymnus and syrphid predators was examined in relation to effectiveness of wax cover of Scymnus against predation from syrphids. Waxless first instar larvae were not protected but wax-covered larvae of second, third and fourth instars were protected from predation by syrphid larvae. The protection was lower in the second instar which has a thin wax cover and significantly higher in the third and fourth instars having a thick wax cover. In addition, larvae from which the wax was removed were significantly more vulnerable to predation. Vulnerability of Scymnus larvae to predation from syrphids was directly related to the thickness of wax cover. Results suggest that the wax cover of Scymnus larvae act as an effective defence mechanism against predation from syrphid larvae.     

Proximate effects of maternal oviposition preferences on defence efficacy and larval survival in a diet‐specialised tortoise beetle. Who knows best: mothers or their progeny?

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Target-oriented dissemination of Beauveria bassiana conidia by the predators,Harmonia axyridis (Coleoptera: Coccinellidae) and Chrysoperla carnea (Neuroptera: Chrysopidae) for biocontrol of Myzus persicae

Dissemination of microbial biocontrol agents via predators may have advantages for safe spore dispersal to targeted pests with the added benefit of predation. A laboratory study was conducted to test the target-oriented dissemination of conidia of Beauveria bassiana using larvae of both the multicoloured Asian lady beetle (Harmonia axyridis) and common green lacewing (Chrysoperla carnea) for control of aphids. Maximum dry conidial attachment occurred within approximately 7 min after exposure. After release of the treated predators on leaves of Chinese cabbage, within 12 hours lacewing larvae dispersed 89% of the attached conidia while Asian lady beetles dispersed 93%. Both predators dispersed conidia up to 2.4 m from the release site. Leaf disk bioassays were conducted to compare two application methods; the dissemination of conidia of B. bassiana by predators and the direct application of conidial suspensions. Mortality in sprayed aphids was 91±2.1% compared to 88±2.1 and 84±4.2%, respectively, when conidia were disseminated by lacewings and lady beetles. Predation was not affected in treated lacewing larvae whereas there was a 20% reduction in predation by lady beetle larvae. It appears that B. bassiana can be effectively delivered using certain insect predators.     

Patterns of herbivory on Passiflora leaf tissues and species by generalized and specialized feeding insects

Abstract.

• 1 The feeding patterns of specialized (Heliconius butterflies) and generalized (the grasshopper, Osmilia flavolineata) herbivores on leaf age classes and species of neotropical vines in the genus Passiflora are compared by offering them leaf discs in choice experiments.
• 2 Heliconius larvae selected young meristematic leaves over medium aged and mature leaves of Passiflora auriculata on which to feed.
• 3 Adults of O. flavolineata consumed more young leaves of P. pittieri from an array of different ages of leaf tissue, but showed no preference for young over mature leaves of P. tetrastylus or P. data.
• 4 In choice tests conducted with medium aged leaves of four species of Passiflora, O. flavolineata selected P. tetrastylus over P. pittieri and P. vitifolia, which were consumed more than P. alata.
• 5 P. alata, which was avoided by O. flavolineata in feeding trials, was the only abundant Passiflora in neotropical habitats where generalized herbivores (grasshoppers and katydids) were common.
• 6 Our results suggest that Passiflora species in forest habitats where some generalized herbivores are rare have fewer chemical defences, but retain physical defences (tough leaves and hooked trichomes) rendering them unpalatable to specialized herbivores like the larvae of Heliconius butterflies.

     

Behavioural responses to predation may explain shifts in community structure

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Larvae of cryptic species of Anopheles gambiae respond differently to cues of predation risk

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Power lines,roads, and avian nest survival: effects on predator identity and predation intensity

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Dying from the lesser of three evils: facilitation and non‐consumptive effects emerge in a model with multiple predators

Prey modify their behaviour to avoid predation, but dilemmas arise when predators vary in hunting style. Behaviours that successfully evade one predator sometimes facilitate exposure to another predator, forcing the prey to choose the lesser of two evils. In such cases, we need to quantify behavioural strategies in a mix of predators. We model optimal behaviour of Atlantic cod Gadus morhua larvae in a water column, and find the minimal vulnerability from three common predator groups with different hunting modes; 1) ambush predators that sit‐and‐wait for approaching fish larvae; 2) cruising invertebrates that eat larvae in their path; and 3) fish which are visually hunting predators. We use a state‐dependent model to find optimal behaviours (vertical position and swimming speed over a diel light cycle) under any given exposure to the three distinct modes of predation. We then vary abundance of each predator and quantify direct and indirect effects of predation. The nature and strength of direct and indirect effects varied with predator type and abundance. Larvae escaped about half the mortality from fish by swimming deeper to avoid light, but their activity level and cumulative predation from ambush predators increased. When ambush invertebrates dominated, it was optimal to be less active but in more lit habitats, and predation from fish increased. Against cruising predators, there was no remedy. In all cases, the shift in behaviour allowed growth to remain almost the same, while total predation were cut by one third. In early life stages with high and size‐dependent mortality rates, growth rate can be a poor measure of the importance of behavioural strategies.     

The impacts of overwintered green frog larvae on wood frog embryo mortality under a wetter climate

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