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opencc-zeroDec 2020View details →

Toxin or medication? Immunotherapeutic effects of nicotine on a specialist caterpillar

1. A core tenant in the field of ecological immunology is that immune responses trade off with other physiological functions due to resource-allocation costs. Caterpillars, for example, tend to exhibit reduced immune responses when reared on more toxic food plants due to a cost from detoxifying or sequestering secondary metabolites, also known as the "vulnerable host hypothesis". However, support for this hypothesis is mixed, and studies have not yet mechanistically isolated the relative contributions of total plant defenses, specific metabolites, or macro-nutritional quality. 2. We used the tobacco hornworm (Manduca sexta), a specialist herbivore on plants in the nightshade family (Solanaceae), to investigate tradeoffs in immune response. This system is ideal given the availability of solanaceous plant lines varying in general (i.e., jasmonate-induced) and specific (i.e., nicotine) resistance traits. We also applied a geometric diet stoichiometry approach to examine how phytochemical toxicity and nutritional quality interactively impact insect immunity and performance. We predicted that as plant toxicity increased immune activity and herbivore performance would decrease. 3. Increasing food plant toxicity reduced insect growth and development, as predicted, but contrary to our hypothesis, plant toxicity did not trade off with immune parameters. Surprisingly, specific plant chemicals, in this case nicotine, appeared immunotherapeutic, stimulating the phenoloxidase (PO) immune response of M. sexta. Available nutrients in artificial diets, mainly protein, also strongly impacted insect growth, but did not affect PO activity, while diets supplemented with nicotine enhanced the PO and melanization response. 4. This work highlights how specific secondary metabolites, and not overall plant toxicity, impact the immune response. Importantly, our data also suggest an alternative mechanism (i.e., immune enhancement) for reduced parasitoid performance when reared from hosts on toxic plants via tri-trophic interactions.

opencc-zeroDec 2020View details →

Role of the intestinal microbiome in polyethylene degradation by caterpillar larva of the greater wax moth (Galleria mellonella)

Recently, a few insects, including the caterpillar larva of the greater wax moth Galleria mellonella, have been identified as avid "plastivores". Interestingly, these caterpillars are able to ingest and metabolize polyethylene at unprecedented rates. While it appears that G. mellonella plays an important role in the biodegradation process, the contribution of its intestinal microbiome remains poorly understood and contested. In a series of experiments, we present strong evidence of an intricate relationship between an intact microbiome, low density polyethylene (LDPE) biodegradation, and the production of glycol as a metabolic by-product. First, we biochemically confirmed that G. mellonella larvae consume and metabolize LDPE, as individual caterpillars fed on polyethylene excreted glycol, but those excretions are reduced by antibiotic treatment. Further, while the gut bacterial communities remain relatively stable regardless of diet, we show that during the early phases of feeding on LDPE (24-72 hrs), caterpillars exhibit increased microbial abundance relative to those starved or fed on their natural honeycomb diet. Finally, by isolating and growing gut bacteria with polyethylene as their exclusive carbon source for over one year, we identified microorganisms in the genus Acinetobacter that appear to be involved in this biodegradation process. Taken collectively, our study indicates that during short term exposure, the intestinal microbiome of G. mellonella is intricately associated with polyethylene biodegradation in vivo.

opencc-zeroDec 2018View details →

Data from: Bacterial communities within Phengaris (Maculinea) alcon caterpillars are shifted following transition from solitary living to social parasitism of Myrmica ant colonies

Bacterial symbionts are known to facilitate a wide range of physiological processes and ecological interactions for their hosts. In spite of this, caterpillars with highly diverse life histories appear to lack resident microbiota. Gut physiology, endogenous digestive enzymes, and limited social interactions may contribute to this pattern, but the consequences of shifts in social activity and diet on caterpillar microbiota are largely unknown. Phengaris alcon caterpillars undergo particularly dramatic social and dietary shifts when they parasitize Myrmica ant colonies, rapidly transitioning from solitary herbivory to ant tending (i.e., receiving protein‐rich regurgitations through trophallaxis). This unique life history provides a model for studying interactions between social living, diet, and caterpillar microbiota. Here, we characterized and compared bacterial communities within P. alcon caterpillars before and after their association with ants, using 16S rRNA amplicon sequencing and quantitative PCR. After being adopted by ants, bacterial communities within P. alcon caterpillars shifted substantially, with a significant increase in alpha diversity and greater consistency in bacterial community composition in terms of beta dissimilarity. We also characterized the bacterial communities within their host ants (Myrmica schencki), food plant (Gentiana cruciata), and soil from ant nest chambers. These data indicated that the aforementioned patterns were influenced by bacteria derived from caterpillars' surrounding environments, rather than through transfers from ants. Thus, while bacterial communities are substantially reorganized over the life cycle of P. alcon caterpillars, it appears that they do not rely on transfers of bacteria from host ants to complete their development.

opencc-zeroDec 2017View details →

Data from: Symbiotic polydnavirus of a parasite manipulates caterpillar and plant immunity

Obligate symbioses occur when organisms require symbiotic relationships to survive. Some parasitic wasps of caterpillars possess obligate mutualistic viruses called "polydnaviruses." Along with eggs, wasps inject polydnavirus inside their caterpillar hosts where the hatching larvae develop inside the caterpillar. Polydnaviruses suppress the immune systems of their caterpillar hosts, which enables egg hatch and wasp larval development. It is unknown whether polydnaviruses also manipulate the salivary proteins of the caterpillar, which may affect the elicitation of plant defenses during feeding by the caterpillar. Here, we show that a polydnavirus of the parasitoid Microplitis croceipes, and not the parasitoid larva itself, drives the regulation of salivary enzymes of the caterpillar Helicoverpa zea that are known to elicit tomato plant-defense responses to herbivores. The polydnavirus suppresses glucose oxidase, which is a primary plant-defense elicitor in the saliva of the H. zea caterpillar. By suppressing plant defenses, the polydnavirus allows the caterpillar to grow at a faster rate, thus improving the host suitability for the parasitoid. Remarkably, polydnaviruses manipulate the phenotypes of the wasp, caterpillar, and host plant, demonstrating that polydnaviruses play far more prominent roles in shaping plant–herbivore interactions than ever considered.

opencc-zeroDec 2016View details →

Data from: No geographic variation in thermoregulatory color plasticity and limited variation in heat-avoidance behavior in Battus philenor caterpillars

Phenotypic plasticity can help organisms cope with variation in their current environment, including temperature variation, but not all environments are equally variable. In the least variable or extreme environments, plasticity may no longer be used. In this case, the plasticity could be lost all together, or it could persist with either the same or an altered reaction norm, depending on factors such as the plasticity's costs. In the pipevine swallowtail caterpillar (Battus philenor), I tested for changes in two forms of heat-avoidance plasticity, color change and refuge-seeking behavior, across the species' range in the United states, including the cooler eastern parts of its range where color change has not been observed and is unlikely to be needed. I found that both heat-avoidance behavior and color change persisted in all surveyed populations. Indeed, the reaction norm for color change remained nearly unaltered, while the threshold for refuge-seeking only changed slightly across populations. These results suggest that the costs of these plastic traits are low enough for them to be maintained by whatever minimal gene flow the population receives. I show that plasticity can be maintained unaltered in populations where it is not used and discuss the potential consequences of this persistence for both the ecology and evolution of plasticity.

opencc-zeroNov 2019View details →

Elevational contrast in predation and parasitism risk to caterpillars in a tropical rainforest

Invertebrate predators and parasitoids are among the most important natural enemies of insect herbivores. Yet, the strength of natural enemy pressure along an altitudinal gradient and interactions between groups of natural enemies (such as predation on parasitized prey) are not well known. Various methods are used to reveal mortality factors of herbivores. Predation pressure is usually assessed through exposure of artificial prey. However, this method cannot provide information about the attacks of parasitoids, or their eventual interactions with predators. Further, artificial or dead prey might not attract predators because they do not show expected host behavior, and this method mostly cannot distinguish between predation and scavenging. For the first time in a tropical rainforest, we quantified mortality factors along an altitudinal gradient using exposure of live caterpillars. We exposed a total of 800 live caterpillars of Talanga excelsalis moresbyensis Strand (Lepidoptera: Crambidae) on saplings of Ficus copiosa Steud. (Moraceae) at two elevations in primary tropical rain forest in Papua New Guinea (200 and 1 200 m a.s.l.). We exposed the caterpillars in two treatments: exposed to and protected from invertebrate predators and parasitoids. Disappearance of caterpillars was significantly higher in the exposed treatment. Further, caterpillar disappearance was significantly higher in lowlands than in highlands (43 vs. 12%). We consider the vast majority of the disappearance to be due to predation, as migration of the caterpillars from the focal trees was not observed (except one caterpillar). This estimate of invertebrate predation rate corresponds with studies which used artificial caterpillar models. No significant difference in parasitism rate between the two elevations was observed (12 vs. 13%). The combination of the disappearance and parasitism rate patterns means that larval parasitoids face stronger pressure from invertebrate predators through higher predation of their hosts in the lowlands than in the highlands.

opencc-zeroDec 2012View details →

Data from: Population dynamics of an Arctiid caterpillar-tachinid parasitoid system using state-space models

1. Population dynamics of insect host–parasitoid systems are important in many natural and managed ecosystems and have inspired much ecological theory. However, ecologists have a limited knowledge about the relative strengths of species interactions, abiotic effects and density dependence in natural host–parasitoid dynamics. Statistical time-series analyses would be more informative by incorporating multiple factors, measurement error and noisy dynamics. 2. We use a novel maximum likelihood and model-selection analysis of a state-space model for host–parasitoid dynamics to examine 21 years of annual census data for woolly bear caterpillars (Platyprepia virginalis) and their locally host-specific tachinid parasitoids (Thelaira americana). 3. Caterpillar densities varied by three orders of magnitude and were driven by density dependence and precipitation from the previous March but not detectably by parasitoids, despite variable and sometimes high (>50%) parasitism. 4. Fly fluctuations, as estimated from per cent parasitism, were affected by density dependence and precipitation from the previous July. There was marginal evidence that host abundance drives fly fluctuations as a generic linear effect but no evidence for classical Nicholson–Bailey coupling. 5. The state-space model analysis includes new methods for likelihood calculation and allows a balanced consideration of effect magnitude and statistical significance in a nonlinear model with multiple alternative explanatory variables.

opencc-zeroDec 2010View details →

Data from: Temperature, size, reproductive allocation, and life-history evolution in a gregarious caterpillar

The present study aimed to investigate the relation between growth rate, final mass and larval development, and how this relations influence the reproductive trade-offs in the context of a gregarious life-style and the need to keep an optimal group size. We use as model two sympatric populations of the pine processionary moth Thaumetopoea pityocampa, occurring in different seasons and thus experiencing different climatic conditions. T. pityocampa is a strictly gregarious caterpillar throughout the larval period, which occurs during winter in countries all over the Mediterranean Basin. However in 1997 a population, in which larval development occurs during the summer, was discovered in Portugal, being called Summer Population SP, as opposed to the normal Winter Population WP, which coexists in the same forest feeding on the same host during the winter. Both this populations were monitored during three years, with assessment of the length of the larval period and its relation with different climatic variables, final mass and adult size, egg size and number, colony size, and mortality in different life stages. The SP larval period was reduced due to development in the warmer part of the year, however reaching the same final mass and adult size as the WP. In spite of equal size at maturity, a trade-off between egg size and number was found between the two populations: SP produced less but bigger eggs than WP. This is the opposite of what is generally found in other Lepidoptera species, where development in colder environments leads to larger eggs at the expense of fecundity, but corroborates the trend found at a macro-geographic scale for T. pityocampa, with females from northern latitudes and colder environment, producing more and smaller eggs. Results point to the importance of number of eggs in cold environments due to an advantage of large colonies when gregarious caterpillars develop in such environments, and are discussed according to the major theories regarding size in animals.

FIGURE 15-18 in Morphology and behaviour of the larva of Calindoea trifascialis (Lepidoptera: Thyrididae), a chemically-defended retreat-building caterpillar from Vietnam

FIGURE 15-18. Larvae and larval retreat of unidentified species of Thyrididae from Queensland, Australia. 15. Habitus of larva with abdominal protuberances concealed. 16. Habitus of larva with abdominal protuberances everted. 17. Mid-stage in the construction of larval retreat. 18. Completed larval retreat. Note: retreat is on underside of leaf.

FIGURE 13 in Morphology and behaviour of the larva of Calindoea trifascialis (Lepidoptera: Thyrididae), a chemically-defended retreat-building caterpillar from Vietnam

FIGURE 13. Template for construction of feeding retreat. Photocopy and follow these steps. 1. Cut out leaf margin. 2. Cut leaf from A to B to C to midpoint between C and C1. 3. Fold A to A1 and seal from O to A/A1. 4. Raise cut portion and attach to leaf surface with C to C1, and B to B1.

FIGURE 12 in Morphology and behaviour of the larva of Calindoea trifascialis (Lepidoptera: Thyrididae), a chemically-defended retreat-building caterpillar from Vietnam

FIGURE 12. Steps in retreat construction. ad. Feeding retreat. See text for discussion. 13 succesive silk struts; X, apex of retreat. eh. Pupation retreat. See text for discussion.

FIGURE 9 in Morphology and behaviour of the larva of Calindoea trifascialis (Lepidoptera: Thyrididae), a chemically-defended retreat-building caterpillar from Vietnam

FIGURE 9. Structure and chaetotaxy of finalinstar larva of Calindoea trifascialis A. Head, T1, T2; B. A1; lateral. C. A3; lateral. D. A8A10; lateral.

FIGURE 10 in Morphology and behaviour of the larva of Calindoea trifascialis (Lepidoptera: Thyrididae), a chemically-defended retreat-building caterpillar from Vietnam

FIGURE 10. Structure and chaetotaxy of finalinstar larva of Calindoea trifascialis. A. Head; frontal. B. Head; lateral. C. Mandible. D. Crochets; arrow pointing to meson. E. Gland associated with abdominal protuberances; internal structure. F. Gland and A1 protuberance, lateral view.

FIGURE 11 in Morphology and behaviour of the larva of Calindoea trifascialis (Lepidoptera: Thyrididae), a chemically-defended retreat-building caterpillar from Vietnam

FIGURE 11. Structure of pupa of Calindoea trifascialis. A. Dorsal. B. Lateral. C. Ventral. D. Detail of spiracular area, internal chamber indicated by broken line.

FIGURES 1-8. Calindoea trifascialis. 1-7 in Morphology and behaviour of the larva of Calindoea trifascialis (Lepidoptera: Thyrididae), a chemically-defended retreat-building caterpillar from Vietnam

FIGURES 1-8. Calindoea trifascialis. 1-7. Final-instar larvae and retreats. 1. Feeding retreat (tent) on leaf of Dipterocarpus tuberculatus. 2. Larva and feeding damage exposed by opening retreat. Note: accumulated frass (right) and partial cutting of leave surface (arrow). 3. Habitus of final instar larva. Note: apices of forward-directed lateral protuberances with glandular secretions (arrow). 4. Oblique view of mid stage in construction of feeding retreat, caterpillar cutting fifth segment of leaf. Note: silk struts hold the leaf in an elevated position. 5. Repairing an opened retreat. 6. Comparison of feeding retreat (right) and pupation retreat (left). Note: exit hole in feeding retreat (arrow). 7. Posterior view of nearly completed pupation retreat, the bottom is not completely sealed. Note: Silken struts. 8. Newly emerged adult.

opencc-zeroDec 2018View details →

Data from: Human-mediated disturbance in multitrophic interactions results in outbreak levels of North America's most venomous caterpillar

Abstract Anthropogenic environmental change is predicted to disrupt multitrophic interactions, which may have drastic consequences for population-level processes. Here, we investigate how a large-scale human-mediated disturbance affects the abundance of North America's most venomous caterpillar species, Megalopyge opercularis. Specifically, we used a natural experiment where netting was deployed to cover the entire canopies of a subset of mature southern live oak trees (Quercus virginiana) to exclude urban pest birds (grackles and pigeons), throughout an 8.1-km2 area encompassing a medical center in Houston, Texas. We used this experimental exclusion to test the following hypothesis: release from avian predators increases caterpillar abundance to outbreak levels, which increases the risk to human health. Results from a multi-year survey show that caterpillar abundance increased, on average, >7300% on netted versus non-netted trees. Thus, increases in caterpillar abundance, due to anthropogenic enemy release, increase human exposure to this venomous pest, and should be considered a health threat in the area. This study emphasizes the unforeseen consequences of ecological disturbance for species interactions and highlights the importance of considering ecology in urban planning.

opennotspecifiedJul 2020View details →

Figure 3 in The tortoise caterpillar: carnivory and armoured larval morphology of the metalmark butterfly Pachythone xanthe (Lepidoptera: Riodinidae)

Figure 3. Scanning electron microscopy of the last instar of Pachythone xanthe. (a,b) Prothoracic plate in external (a) and internal (b) views; (c) head capsule in lateral view.

opennotspecifiedJul 2020View details →

Figure 2 in The tortoise caterpillar: carnivory and armoured larval morphology of the metalmark butterfly Pachythone xanthe (Lepidoptera: Riodinidae)

Figure 2. Scanning electron microscopy of the penultimate instar of Pachythone xanthe. (a) Lateral view, arrow pointing the tentacle nectary organ (TNOs) openings; (b) semi-open prothoracic plates in frontal view showing the head; (c) head and thorax in lateroventral view; (d) prothoracic spiracle; (e) detail of head in frontal view; (f) cluster of perforated cupola organs (PCOs), glandular openings and arborescent setae on the prothorax; (g) detail of dorsal cluster of cone-like setae on the A3 abdominal segment; (h) detail of lateral fringe setae; (i) A4 abdominal spiracle; (j) TNO in lateral view, note opening surrounded by PCOs; (k) detail of specialised setae on TNO.

opennotspecifiedJul 2020View details →

Figure 1 in The tortoise caterpillar: carnivory and armoured larval morphology of the metalmark butterfly Pachythone xanthe (Lepidoptera: Riodinidae)

Figure 1. Natural history of Pachythone xanthe and symbiotic interactions with Azteca cf. chartifex ants and scale insects on a Miconia sp. tree. (a,b), penultimate instar in lateral (a) and dorsal (b) views, note the tentacle nectary organs (TNOs) openings (arrows); (c–f) last instar preying on ant-tended scale insects (yellow arrow) (c), resting posture (d), and frontal views showing the prothoracic plates closed (e) and open revealing the head (f); (g,h) pupa in lateral (g) and dorsal (h) views; (i) freshly emerged adult.