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.     

High densities of leaf‐tiers in open habitats are explained by host plant architecture

1. Crown architecture remains one of the least studied plant traits that influence plant–herbivore interactions. The hypotheses that dense crown architecture of mountain birches from open habitats favours leaf‐tying caterpillars through bottom‐up and/or top‐down effects associated with high leaf connectivity were tested. 2. Population densities of leaf‐tying herbivores in open (industrial barren and seashore) habitats were three times as high as in the shaded (forest) habitats. An experimental increase in leaf density by branch binding did not affect foliar consumption by free‐living herbivores but increased consumption by leaf‐tiers. 3. The specific leaf weight was lower in shaded habitats and in bound branches, but branch binding did not influence either the foliar concentrations of carbon and nitrogen or the pupal weight of the most abundant leaf‐tier, Carpatolechia proximella Hbn. (Lepidoptera: Gelechiidae). 4. Caterpillars of C. proximella build several shelters during their lifetime and spend a considerable amount of time outside the shelter, where they excrete most of their faeces. In bound branches, caterpillars built new shelters more frequently than in control branches, and consumed less foliar biomass per shelter. 5. Mortality from parasitoids in bound branches was half that in the control, presumably because the complex environment disrupted parasitoid searching behaviour and/or because of lower damage to leaves from which the shelters were built. 6. It is concluded that the crown architecture associated with high leaf connectivity decreases mortality risks from natural enemies both outside and inside the shelter. Compact and dense crowns of host plants may at least partly explain high population densities of leaf‐tiers in open habitats.     

Ecological consequences of shelter sharing by leaf-tying caterpillars

A wide variety of insect herbivores construct and inhabit leaf shelters (ties, rolls, folds, and webs). Shelter construction can lead to a high rate of secondary occupation by other arthropods, including other species of constructors. The consequences for the inhabitants of secondarily occupying these shelters are currently unknown. In this study, we conducted field experiments to examine the fitness consequences (survival and attack by natural enemies) for caterpillars that (i) occupy a shelter with conspecifics vs. occur singly; and (ii) establish a new shelter vs. colonize a pre‐existing one. In addition, we conducted factorial laboratory experiments to test the hypothesis that caterpillars sharing shelters with conspecifics might have reduced construction costs (a potential benefit of shelter‐sharing or secondary occupation). Larvae of Psilocorsis quercicella Clemens (Lepidoptera: Oecophoridae) placed in white oak [Quercus alba L. (Fagaceae)] leaf ties alone or in groups of three had equal likelihood of survival from natural enemies. This same caterpillar species, however, had a higher disappearance rate when placed in pre‐existing leaf ties than when placed in newly formed ones, suggesting a potential cost of secondary colonization. A similar experiment with a closely related species [Psilocorsis cryptolechiella (Chambers)], however, failed to detect a cost of secondarily occupying shelters made on beech, Fagus grandifolia Ehrh. (Fagaceae). In the laboratory experiment, we found no evidence of shelter‐sharing benefits; rather larvae reared in shelters in groups of three had lower pupal mass (and thus lower potential fecundity) than larvae reared singly, suggesting a cost of shelter sharing. Moreover, groups of larvae forced to repeatedly construct new shelters tended to have reduced survival relative to the other treatment, suggesting that energetic constraints are more likely to reduce fitness when larvae cohabit shelters. Taken together, these results indicate that the common phenomenon of shelter sharing by leaf‐tying caterpillars has either neutral or negative effects for the occupants. The fact that these leaf‐tying caterpillars actually share shelters may simply reflect limited availability of oviposition sites.     

Shelter-building caterpillars in the cerrado: seasonal variation in relative abundance, parasitism, and the influence of extra-floral nectaries

Caterpillar shelters provide protection against desiccation and natural enemies, whereas extra-floral nectaries (EFNs) may be an anti-herbivore adaptation that reduces herbivore abundance by attracting predators and parasites. We used a large, long-term dataset for caterpillars found in the Brazilian cerrado to examine temporal variations in the relative abundance of shelter-building caterpillars and exposed caterpillars, and to determine how much variation depends on the season and the presence of EFNs on host plants. We also compared the patterns of parasitism between sheltered and exposed caterpillars, between seasons, and between different host plants. The cerrado has a marked dry season, and its vegetation is a mixture of mostly deciduous shrubs and trees. Leaf production occurs mainly during the rainy season, and many plant species bear EFNs. Our results show that 60?% of cerrado caterpillars build shelters. These caterpillars were found to be proportionally more abundant during the dry season and less parasitized than exposed ones. The proportion of caterpillars building shelters was highest on plants with new leaves (functional EFNs), and parasitism of caterpillars on these plants was higher. Even though our study includes a taxonomically diverse suite of caterpillars that build many different types of shelter and a diverse set of plants and EFN types, our results suggest that EFNs play an important role in structuring caterpillar assemblages in the cerrado, and that the prolific use of shelters by caterpillars may be a result of their effectiveness in protecting caterpillars from natural enemies and desiccation.     

Species composition and life histories of shelter-building caterpillars on Salix miyabeana

We studied the species composition and life history patterns of shelter‐building microlepidoptera on the willow Salix miyabeana in Hokkaido, northern Japan. We identified 23 microlepidopteran species across seven families that constructed leaf shelters. Species in Tortricidae and Pyralidae comprised approximately 90% of the total number of sampled shelter‐building microlepidoptera that reached adult eclosion in the laboratory. Seasonal changes in the density of leaf shelters showed two peaks: early June and mid‐August. In June, caterpillars of Gypsonoma bifasciata, Gypsonoma ephoropa, Acleris issikii and Saliciphage acharis were the principal shelter builders, while in August shelters were constructed primarily by caterpillars of Nephopterix adelphella, A. issikii and S. acharis. Approximately 90% of leaf shelters were constructed on the top portions of shoots, suggesting that most shelter‐building caterpillars prefer to build leaf shelters here.     

Contrasting engineering effects of leaf‐rolling caterpillars on a tropical mite community

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Indirect interactions mediated by leaf shelters in animal–plant communities

Leaf shelters indirectly mediate interactions in animal–plant communities by providing the occupants with several kinds of benefits, as physical ecosystem engineering. The occupants benefit from favorable microhabitat, reduction in antiherbivore defense, and protection from natural enemies. The primary shelter maker has to spend energy and time and producing silk, but shelter users have great advantages without incurring costs. Shelter users consist of a wide range of arthropod taxa and can be divided into two groups: coexisting organisms that live with a primary shelter maker in the same shelter, and secondary users, which inhabit a leaf shelter after it is utilized by a shelter maker. Leaf shelters mediate interactions between (1) primary shelter makers and coexisting organisms or (2) primary shelter makers and secondary users, (3) secondary users, (4) shelter users and their natural enemies, and (5) primary shelter makers, secondary users, and their host plants. Most interactions between primary shelter makers and coexisting organisms constitute a direct trophic linkage rather than indirect ones. There are actually unidirectional beneficial effects from a primary shelter maker to secondary shelter users, whereas leaf shelters mediate competition and predation among shelter users. By providing a leaf shelter, a shelter maker leads to increased diversity of interactions. Leaf shelters modify the distribution of organisms on the host plant and influence herbivory on the host plant. In tritrophic interactions, leaf shelters act as cues for natural enemies that search for a shelter user as prey. Furthermore, by enhancing habitat heterogeneity, leaf shelters affect the abundance and species richness of arthropods on host plants. Received: July 24, 2000 / Accepted: February 15, 2001     

Effects of predation risk and plant resistance on Manduca sexta caterpillar feeding behaviour and physiology

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Costly leaf shelters protect moth pupae from parasitoids

Many caterpillars construct shelters by folding leaves and feeding from within. Many shelter-constructing species suffer high rates of parasitism as larvae or pupae. In spite of the likely significance, the effects of these shelters on the survival of pupae and the trade-off between feeding and constructing shelters have attracted little experimental attention. In both field and laboratory experiments, fern-feeding caterpillars [Herpetogramma theseusalis (Walker) (Lepidoptera: Crambidae)] invested heavily in shelters, losing weight and significantly delaying pupation rather than feeding or pupating in exposed locations. Experimentally thinning the walls of shelters in the field doubled the parasitism rate. Parasitism of pupae exceeded predation by an order of magnitude or more in both seasons of this study. Caterpillars constructed similarly sized shelters regardless of availability of fern fronds, resulting in incomplete shelters on especially small fronds, putting pupae at increased risk of parasitism. We suggest that similar interactions are common and merit more attention.     

Opposing effects of spring defoliation on late season oak caterpillars

ABSTRACT. 1. The pedunculate oak, Quercus rohur L., suffers high annual levels of spring defoliation in Wytham Woods. near Oxford.
2. This spring defoliation affects late season caterpillars through a variety of damage-induced changes in the leaves.
3. Diurnea fagella (D. & S.), one of the commonest late season caterpillars, shows reduced larval survival and pupal weight on regrowth foliage when compared to undamaged primary foliage.
4. D. fagella also suffer higher larval mortality on naturally damaged primary foliage than they do on undamaged foliage.
5. Despite this, the three commonest late season caterpillar species are more abundant on damaged trees than undamaged ones. and their distributions are biased towards damaged leaves within the canopy.
6. Other factors that may be more important than leaf damage in determining the distribution and abundance of late season caterpillars are discussed. D.fagella larvae spin their larval refuges more rapidly on damaged than undamaged foliage, and this may reduce mortality by natural enemies, or ameliorate adverse effects of weather.     

Leaf trenching by Indian red admiral caterpillars for feeding and shelter construction

Many folivorous insects sever leaf veins, trench across leaf blades, or girdle petioles prior to feeding on leaves. The purpose of these behaviours is generally thought to be sabotage of the anti-herbivore chemical defences of host plants. For insects that construct leaf shelters, these behaviours may make leaves easier to roll or fold. Larvae of the Indian red admiral butterfly, Vanessa indica (Herbst), cut trenches at the base of host plant leaves and construct leaf-fold shelters. I attempted to determine which of the above functions the trenching behaviour of V. indica larvae serves. If the function of trenching is to facilitate leaf-folding, then larvae should cut trenches before folding leaves. When the larvae used larger leaves, they tended to trench them prior to folding them. This suggests that the function of trenching behaviour is to make leaves easier to fold. However, larvae sometimes cut trenches after folding the leaves, suggesting that this behaviour has additional functions. When the larvae were about to moult or pupate, they did not cut trenches, suggesting that trenching behaviour may also be involved in feeding.     

Residency Duration and Shelter Quality Influence Vibratory Signalling Displays in A Territorial Caterpillar

Residents are more likely to win territorial disputes than intruders. One explanation for this prior resident advantage is that residents place a higher value on the resource and are therefore more motivated to win. Although value asymmetry models of animal contests often assume that contestants use information about resource value, information on the proximate cues affecting territorial behaviour is often lacking. We use a simple model system – territorial behaviour in the masked birch caterpillar (Drepana arcuata) to identify factors that affect territorial behaviour. Late instar caterpillars occupy solitary silken leaf shelters, which they defend against wandering conspecifics with a vibratory display. We evaluated how a caterpillar identifies itself as the owner and the factors that influence a resident's motivation to signal. To do so, we conducted three experiments between size‐matched residents and intruders to assess how residency duration and shelter quality independently affected territorial displays during the early stages of a contest. Experiment 1 (Time Exp.) demonstrated that resident signalling rates increase with increased duration on the leaf prior to introducing the intruder. Residents also signal more than intruders after residency periods of 1–3 min and longer, demonstrating that residents gather information about resource value shortly after occupying a leaf. Experiment 2 (Squatter Exp.) aimed to disentangle the effects of time on the leaf and silk accumulation. Squatters (individuals in a shelter made by another) placed for 1–3 min on a leaf containing a full silk shelter signalled more to intruders than did caterpillars placed on a fresh leaf for 1–3 min. Experiment 3 (Shelter Removal Exp.) showed that residents whose shelters had been removed signal less than those occupying an intact shelter, despite an equal length of time investing in them. Our experiment is the first to covary both prior residency duration and territory quality, and we find that the motivation of caterpillars to signal is a function of both of these attributes.     

Host plant phenology may determine the abundance of an ecosystem engineering herbivore in a tropical savanna

1. Variation in plant phenology allows plants to escape from herbivory. Insect herbivores manipulate their host plants by producing shelters, which they inhabit, and are protected against natural enemies and/or unfavourable environmental conditions. Environmental modifications induced by living organisms are characterised as ecosystem engineering. 2. In the Brazilian savanna, the interaction between the Malpighiaceae shrub, Byrsonima intermedia, and its main herbivore, the caterpillar Cerconota achatina, a shelter‐building organism, was studied. 3. It was focused on whether the phenological development of the host plant affects the caterpillars' infestation, and whether C. achatina acts as an ecosystem engineer by building shelters. All plant variables (number of leaves, flowers, buds, fruits and herbivores) were measured fortnightly. Phenological data were correlated with climatic information. The impact of the caterpillars acting as ecosystem engineers was measured experimentally. 4. Infestation levels of C. achatina covaried with the phenology of their host plant B. intermedia. It suggests that plant phenology might be an important factor in determining the abundances of this ecosystem engineer species.     

A single lycaenid caterpillar gets an ant‐constructed shelter and uninterrupted ant attendance

Ant‐lycaenid associations range from mutualism to parasitism and the caterpillars of some species of lycaenids are reported to enter ant nests for shelter, diapause, or pupation. The present study aimed to examine the nature of the association between Euchrysops cnejus (Fabricius) (Lepidoptera: Lycaenidae) and Camponotus compressus (Fabricius) (Hymenoptera: Formicidae) worker ants on the extrafloral nectary‐bearing cowpea plant, Vigna unguiculata (L.) Walp. (Fabaceae). The abundance patterns of the ants and the lycaenid caterpillars together with the spatial patrolling patterns of the ants on the plants revealed that ant abundance increased with the occurrence of the lycaenid caterpillars and the ants preferred the lycaenids over the extrafloral nectar. Camponotus compressus worker ants constructed a shelter at the cowpea plant base after interaction with one or more lycaenid caterpillar(s) and tended the caterpillars and pupae till the emergence of the butterfly. The ant‐constructed shelters (ACSs) inhabited by the minor caste workers (13 ± 1.3 ants per ACS), were utilized by the caterpillars to undergo pupation. The ants confined their activities predominantly to tending the pod‐feeding caterpillars and the solitary pupa within each ACS. It appears that the behavior of the tending worker ants is modulated by the lycaenid vulnerable stages.     

Communication of leaf suitability by gregarious eastern tent caterpillars (Malacosoma americanum)

ABSTRACT. 1. Previous work has shown that leaf age affects recruitment trail marking by eastern tent caterpillars ( Malacosoma americanum Fabr.). Young leaves of host plants elicit trail marking to a greater degree than mature leaves.
2. Experiments were conducted to establish the relationship between the differential behavioural responses of larvae to young and mature leaves and the suitability of foliage for larval growth and survival. Foliage of black cherry ( Prunus serotina Ehrh.), a typical rosaceous host plant, was used for this comparison.
3. Larvae preferred young leaves to mature leaves in choice tests, and marked more to young leaves than to mature leaves in no-choice tests.
4. Mature leaves supported adequate growth through two larval instars of rearing, but thereafter were unsuitable for growth. Larvae fed mature leaves had lower pupal weight, poorer survival, and grew less efficiently than larvae fed young leaves.
5. The results support the hypothesis that the trail communication system of eastern tent caterpillars is an adaptation to efficiently locate leaves which are favourable for larval growth and survival.     

To mate or not to mate,and subsequent host search by a haplodiploid female parasitoid wasp

Mated females of haplodiploid species can vary the sex ratio of their offspring, but virgin or sperm‐depleted females can produce only males. Depending on the costs and benefits, the theory of constrained sex allocation states that female haplodiploids may vary in their propensity to mate, with important implications for the populations’ sex ratio. Unmated female parasitoid wasps Alabagrus texanus (Braconidae) have been observed to reject matings with males, even under highly confined spatial conditions. We performed field trials to determine whether unmated female A. texanus would mate. We then compared the preferences of the resulting unmated (constrained) and mated (unconstrained) female wasps for shelters constructed and occupied by their hosts, fern moth caterpillars Herpetogramma theseusalis (Crambidae) on fern fronds. We presented the wasps with pairs of shelters collected from the field that differed in size, as well as freshness, fern species, and presence or absence of caterpillars. Unconstrained females searched small shelters more frequently than did constrained females and tended to favor senesced (old) shelters over fresher ones. They did not differ in choice between shelters on marsh and sensitive ferns or between shelters containing caterpillars and empty shelters. The preference for small shelters by the unconstrained wasps may enhance their rate of contacting favorable hosts, but the foraging regime of the constrained females should expose them to caterpillars at sites infrequently searched by the unconstrained females.     

Behavioural ecology of defence in a risky environment: caterpillars versus ants in a Neotropical savanna

1. Predatory ants may reduce infestation by herbivorous insects, and slow‐moving Lepidopteran larvae are often vulnerable on foliage. We investigate whether caterpillars with morphological or behavioural defences have decreased risk of falling prey to ants, and if defence traits mediate host plant use in ant‐rich cerrado savanna. 2. Caterpillars were surveyed in four cerrado localities in southeast Brazil (70–460 km apart). The efficacy of caterpillar defensive traits against predation by two common ant species (Camponotus crassus, C. renggeri) was assessed through experimental trials using caterpillars of different species and captive ant colonies. 3. Although ant presence can reduce caterpillar infestation, the ants' predatory effects depend on caterpillar defence traits. Shelter construction and morphological defences can prevent ant attacks (primary defence), but once exposed or discovered by ants, caterpillars rely on their size and/or behaviour to survive (secondary defence). 4. Defence efficiency depends on ant identity: C. renggeri was more aggressive and lethal to caterpillars than C. crassus. Caterpillars without morphological defences or inside open shelters were found on plants with decreased ant numbers. No unsheltered caterpillar was found on plants with extrafloral nectaries (EFNs). Caterpillars using EFN‐bearing plants lived in closed shelters or presented morphological defences (hairs, spines), and were less frequently attacked by ants during trials. 5. The efficiency of defences against ants is thus crucial for caterpillar survival and determines host plant use by lepidopterans in cerrado. Our study highlights the effect of EFN‐mediated ant‐plant interactions on host plant use by insect herbivores, emphasizing the importance of a tritrophic viewpoint in risky environments.     

Picking personalities apart: estimating the influence of predation,sex and body size on boldness in the guppy Poecilia reticulata

Predation is a strong selective force in most natural systems, potentially fueling evolutionary changes in prey morphology, life history and behaviour. Recent work has suggested that contrasting predation pressures may lead to population differentiation in personality traits. However, there are indications that these personality traits also differ between sexes and not necessarily in a consistent way between populations. We used an integrative approach to quantify boldness (latency to emerge from a shelter) in wild‐caught guppies in relation to predation pressure, population origin, sex and size. In addition we quantified the repeatability of these personality traits. We show that predation regime had significant effects on emergence time. In general, fish from high predation localities emerged sooner from the shelter compared to those from low predation localities. We found strong sex differences; males were significantly bolder than females. The relationship between emergence time and body size was non‐significant in all populations. We discuss what responses to expect from predator‐naïve versus predator‐experienced individuals and how this can be linked to the shyness–boldness continuum.     

Acoustic stimuli from predators trigger behavioural responses in aggregate caterpillars

Prey detect their predators through predator signals and cues and, consequently, respond with anti‐predatory behaviours to inhibit the action of their aggressors. Lepidopterans can intercept signals emitted by predators and may defend themselves through chemical, morphological or behavioural responses. In this study, we investigated the effect of acoustic stimuli of different predators on defensive behaviour of gregarious caterpillars. Our results demonstrated that Hylesia nigricans (Lepidoptera, Saturniidae) caterpillars alter their behaviour (i.e. abruptly raising the head) in response to the acoustic stimulus of the predators (i.e. predation risk signals from birds and wasps). The magnitude of this response depended on predator identity and caterpillar body size. Larger caterpillars responded more strongly to predatory stimuli than smaller caterpillars. However, regardless of the size of the caterpillars, they responded more strongly to the stimuli of wasps. In addition, we identified that H. nigricans caterpillars emit ultrasonic noise after detecting the stimuli of the predators – this noise seems to function as an alert about the risk of predation during the early stages of development (second and fifth instars). The duration of ultrasonic emission (i.e. milliseconds) increases with the number of repetitions of the stimuli (i.e. wing‐beat sounds of the wasps and insectivorous birds). These results provide novel information about predation risk in interactions among caterpillars and their predators, and indicate possible communication among invertebrates mediated by the risk of predation.     

Adaptive trade-offs of leaf folding in Dichomeris caterpillars on goldenrods

Abstract.

• 1 Leaf folding is a common behaviour among caterpillars that has many potential benefits such as creation of a favourable microclimate and protection from predation or dislodgment.
• 2 One cost of leaf folding which has not previously been quantified is the reduction in growth rate that might result from the energetic expenditures of producing silk and applying it to fold leaves.
• 3 On caged goldenrods in field and forest habitats, early-instar Dichomeris leuconotella (Busck) caterpillars that were repeatedly forced to spin new leaf refuges (either folds or webs of silk) actually had higher growth rates than caterpillars left undisturbed.
• 4 This surprising result apparently reflected the fact that disturbed caterpillars chose relatively young green leaves for new refuges, whereas undisturbed caterpillars tended to remain in their webs or folds on ageing leaves.
• 5 In a glasshouse experiment using plants that underwent little senescence, growth rates were unaffected by the amout of refuge-making effort, indicating that the costs of such effort were either negligible or easily compensated for by these caterpillars.
• 6 On glasshouse plants, caterpillars periodically forced to change refuges had higher disappearance rates than those left undisturbed, despite the absence of predators. Wandering or falling from plants is evidently a major hazard of frequent refuge changes.
• 7 Thus, early-instar Dichomeris caterpillars face a trade-off in which risks of predation or loss of contact with the host favour the observed low rate of refuge changes, but in which growth rates could actually be improved with more refuge changes.