Opposing deer and caterpillar foraging preferences may prevent reductions in songbird prey biomass in historically overbrowsed forests

Overbrowsing by ungulates decimates plant populations and reduces diversity in a variety of ecosystems, but the mechanisms by which changes to plant community composition influence other trophic levels are poorly understood. In addition to removal of avian nesting habitat, browsing is hypothesized to reduce bird density and diversity through reduction of insect prey on browse‐tolerant hosts left behind by deer. In this study, we excluded birds from branches of six tree species to quantify differences in songbird prey removal across trees that vary in deer browse preference. Early in the breeding season, birds preyed on caterpillars at levels proportional to their abundance on each host. Combining these data with tree species composition data from stands exposed to experimentally controlled deer densities over 30 years ago, we tested whether overbrowsing by white‐tailed deer reduces prey biomass long after deer densities are reduced. Our analysis predicts total prey availability in the canopy of regenerating forests is fairly robust to historic exposure to high deer densities, though distribution of prey available from host species changes dramatically. This predicted compensatory effect was unexpected and is driven by high prey abundance on a single host tree species avoided by browsing deer, Prunus serotina. Thus, while we confirm that prey abundance on host trees can act as a reliable predictor for relative prey availability, this study shows that quantifying prey abundance across host trees is essential to understanding how changes in tree species composition interact with ungulate browse preference to determine prey availability for songbirds.     

Ecological diversity of edible insects and their potential contribution to household food security in Haut‐Katanga Province,Democratic Republic of Congo

Democratic Republic of the Congo (DR Congo) has a wide diversity of edible insects making it one of the most important biodiversity hot spots in Africa. The aim of this study was to give the first insight into the food plant range, seasonal availability of edible insects, community preference and willingness to consume them. The study revealed a list of eleven edible insect species belonging to four families. Twenty‐six plant species were recorded as food plants of nine edible caterpillar species. Seasonal availability of these insects coincided with the rainy season and was strongly linked to relatively high level of consumption. The caterpillars Elaphrodes lactea Gaede, Lobobunaea saturnus Fabricius and Cinabra hyperbius (Westwood) as well as the termites Macrotermes falciger Gerstäcker were the most dominant species of edible insects preferred and consumed among the different communities. Our study demonstrates that entomophagy is a common practice among the ethnic populations with married, tertiary and university‐level individuals recording significantly higher consumption of edible caterpillars. Populations between the ages of 18 and 45 years as well as the Bemba tribe were also more actively involved in entomophagy. Further research would be necessary to exploit edible insect biodiversity and ethno‐entomophagy and initiate actions for food plant conservation in DR Congo.     

Traditional Regulation of Edible Caterpillar Exploitation in the Kopa Area of Mpika District in Northern Zambia

The Traditional Ecological Knowledge (TEK) of the Bisa people of northern Zambia on species, life cycles and host plants of the caterpillars they exploit for food and for household income generation, and the traditional control of caterpillar harvesting, were investigated through a household survey. The accessed indigenous knowledge on caterpillar biology was validated through a forest survey, caterpillar collections and identifications. Eight species of caterpillars were harvested from the surrounding miombo woodlands. Their life systems and host plants were well understood by members of local communities and this knoweldge was communicated amongst them orally. Popular commercial species were Gynanisa maya Strand and Gonimbrasia zambesina Walker. Over 20 miombo tree species hosted the two species but the mean numbers of the caterpillars on Julbernadia paniculata Troupin were significantly larger than those on other host plants (p < 0.05), indicating that J. paniculata was probably the main host plant of the two species. Traditional regulation of caterpillar harvesting involved: (i) monitoring for edible caterpillar development and abundance and for changes in caterpillar habitats, (ii) protection of host plants and moth eggs against late bush fires, through use of traditional fire technology, and (iii) temporal restriction of edible caterpillar harvesting. The possibility of the Zambian Government promoting caterpillar harvesting as an economic incentive to the Bisa people to conserve both this renewable edible caterpillar natural resource and their environment is discussed.     

Tree diversity and functional leaf traits drive herbivore‐associated microbiomes in subtropical China

Herbivorous insects acquire microorganisms from host plants or soil, but it remains unclear how the diversity and functional composition of host plants contribute to structuring herbivore microbiomes. Within a controlled tree diversity setting, we used DNA metabarcoding of 16S rRNA to assess the contribution of Lepidoptera species and their local environment (particularly, tree diversity, host tree species, and leaf traits) to the composition of associated bacterial communities. In total, we obtained 7,909 bacterial OTUs from 634 caterpillar individuals comprising 146 species. Tree diversity was found to drive the diversity of caterpillar‐associated bacteria both directly and indirectly via effects on caterpillar communities, and tree diversity was a stronger predictor of bacterial diversity than diversity of caterpillars. Leaf toughness and dry matter content were important traits of the host plant determining bacterial species composition, while leaf calcium and potassium concentration influenced bacterial richness. Our study reveals previously unknown linkages between trees and their characteristics, herbivore insects, and their associated microbes, which contributes to developing a more nuanced understanding of functional dependencies between herbivores and their environment, and has implications for the consequences of plant diversity loss for trophic interactions.     

Timing of breeding and nestling diet of Wood Warbler Phylloscopus sibilatrix in relation to changing food supply

Capsule Wood Warblers did not match their reproduction to the caterpillar peak

Aims To study the timing of Wood Warblers’ breeding and nestling diet in relation to caterpillar abundance under primeval conditions in the Bia?owie?a National Park, Poland.

Methods Observations of food brought by parents. Inter‐year and seasonal changes in availability of folivorous caterpillars were assessed by direct counts and caterpillar frass collection.

Results Maximum food requirements occurred two weeks after the peak of caterpillar abundance. The mismatch had no effect on nestlings’ development. Diet varied little across years and habitats, but varied strongly within a season. Following the decline of ‘green’ caterpillars, their proportion in the Wood Warbler diet strongly declined. Caterpillars were replaced by winged insects. Small nestlings received more spiders than older ones.

Conclusion Timing of Wood Warbler breeding in Bia?owie?a National Park was constrained by the females’ arrival time. Birds did not match their reproduction to the caterpillar peak. ‘Green’ caterpillars were the preferred food for nestlings; birds responded to the caterpillar decrease by feeding smaller proportions of them and switching to alternative prey, namely winged insects.     

The ecology of predispersal insect herbivory on tree reproductive structures in natural forest ecosystems

Plant-insect interactions are key model systems to assess how some species affect the distribution, the abundance, and the evolution of others. Tree reproductive structures represent a critical resource for many insect species, which can be likely drivers of demography, spatial distribution, and trait diversification of plants. In this review, we present the ecological implications of predispersal herbivory on tree reproductive structures by insects (PIHR) in forest ecosystems. Both insect's and tree's perspectives are addressed with an emphasis on how spatiotemporal variation and unpredictability in seed availability can shape such particular plant-animal interactions. Reproductive structure insects show strong trophic specialization and guild diversification. Insects evolved host selection and spatiotemporal dispersal strategies in response to variable and unpredictable abundance of reproductive structures in both space and time. If PIHR patterns have been well documented in numerous systems, evidences of the subsequent demographic and evolutionary impacts on tree populations are still constrained by time-scale challenges of experimenting on such long-lived organisms, and modeling approaches of tree dynamics rarely consider PIHR when including biotic interactions in their processes. We suggest that spatially explicit and mechanistic approaches of the interactions between individual tree fecundity and in sect dynamics will clarify predictions of the demogenetic implications of PIHR in tree populations. In a global change context, further experimental and theoretical contributions to the likelihood of life-cycle disruptions between plants and their specialized herbivores, and to how these changes may gen erate novel dynamic patterns in each partner of the interaction are increasingly critical.     

Abundance trumps quality: bi‐trophic performance and parasitism risk fail to explain host use in the fall webworm

Factors including host abundance, quality, and the degree to which hosts provide enemy‐free space (EFS) may drive host plant choice by phytophagous insects. Herbivores may also experience fitness tradeoffs among hosts, promoting polyphagy. The fall webworm Hyphantria cunea is a dietary generalist that feeds on a broad array of trees across its geographic range. Here, we investigate the drivers of host tree use by the fall webworm in Connecticut (CT) and Maryland (MD). Neither caterpillar performance nor EFS was associated with the frequency with which host trees were used, and no tradeoff between host quality and EFS was identified. Vegetation surveys adjacent to host trees showed that at both localities, host use was non‐random with respect to tree species, and that the main predictor of use among suitable host trees was host tree abundance. This suggests that webworms are under selection to reduce search time for oviposition sites. Although we did not detect a tradeoff between host plant quality and availability in MD, we did identify that tradeoff in CT. This disparity amid otherwise similar patterns of host use between CT and MD may be explained by the relative rarity of high quality hosts in CT compared to MD. Our results illustrate that geographic mosaics in patterns of host use may arise in the absence of local adaptation if host use is based upon availability rather than host plant attributes.     

Acquiring nutrients from tree leaves: effects of leaf maturity and development type on a generalist caterpillar

The rapid growth and prolific reproduction of many insect herbivores depend on the efficiencies and rates with which they acquire nutrients from their host plants. However, little is known about how nutrient assimilation efficiencies are affected by leaf maturation or how they vary between plant species. Recent work showed that leaf maturation can greatly decrease the protein assimilation efficiency (PAE) of Lymantria dispar caterpillars on some tree species, but not on species in the willow family (Salicaceae). One trait of many species in the Salicaceae that potentially affects PAE is the continuous (or “indeterminate”) development of leaves throughout the growing season. To improve our understanding of the temporal and developmental patterns of nutrient availability for tree-feeding insects, this study tested two hypotheses: nutrients (protein and carbohydrate) are more efficiently assimilated from immature than mature leaves, and, following leaf maturation, nutrients are more efficiently assimilated from indeterminate than determinate tree species. The nutritional physiology and growth of a generalist caterpillar (L. dispar) were measured on five determinate and five indeterminate tree species while their leaves were immature and again after they were mature. In support of the first hypothesis, caterpillars that fed on immature leaves had significantly higher PAE and carbohydrate assimilation efficiency (CAE), as well as higher protein assimilation rates and growth rates, than larvae that fed on mature leaves. Contrary to the second hypothesis, caterpillars that fed on mature indeterminate tree leaves did not have higher PAE than those that fed on mature determinate leaves, while CAE differed by only 3% between tree development types. Instead, “high-PAE” and “low-PAE” tree species were found across taxonomic and development categories. The results of this study emphasize the importance of physiological mechanisms, such as nutrient assimilation efficiency, to explain the large variation in host plant quality for insect herbivores.     

Fine spatial pattern of an epiphytic lichen species is affected by habitat conditions in two forest types in the Iberian Mediterranean region

Persistence and abundance of species is determined by habitat availability and the ability to disperse and colonize habitats at contrasting spatial scales. Favourable habitat fragments are also heterogeneous in quality, providing differing opportunities for establishment and affecting the population dynamics of a species. Based on these principles, we suggest that the presence and abundance of epiphytes may reflect their dispersal ability, which is primarily determined by the spatial structure of host trees, but also by host quality. To our knowledge there has been no explicit test of the importance of host tree spatial pattern for epiphytes in Mediterranean forests. We hypothesized that performance and host occupancy in a favourable habitat depend on the spatial pattern of host trees, because this pattern affects the dispersal ability of each epiphyte and it also determines the availability of suitable sites for establishment. We tested this hypothesis using new point pattern analysis tools and generalized linear mixed models to investigate the spatial distribution and performance of the epiphytic lichen Lobaria pulmonaria, which inhabits two types of host trees (beeches and Iberian oaks). We tested the effects on L. pulmonaria distribution of tree size, spatial configuration, and host tree identity. We built a model including tree size, stand structure, and several neighbourhood predictors to understand the effect of host tree on L. pulmonaria. We also investigated the relative importance of spatial patterning on the presence and abundance of the species, independently of the host tree configuration. L. pulmonaria distribution was highly dependent on habitat quality for successful establishment, i.e., tree species identity, tree diameter, and several forest stand structure surrogates. For beech trees, tree diameter was the main factor influencing presence and cover of the lichen, although larger lichen-colonized trees were located close to focal trees, i.e., young trees. However, oak diameter was not an important factor, suggesting that bark roughness at all diameters favoured lichen establishment. Our results indicate that L. pulmonaria dispersal is not spatially restricted, but it is dependent on habitat quality. Furthermore, new spatial analysis tools suggested that L. pulmonaria cover exhibits a distinct pattern, although the spatial pattern of tree position and size was random.     

Galling insects in a fragmented forest: incidence of habitat loss,edge effects and plant availability

Galling insects tend to be highly sensitive to changes in their host plants or their environment. Here we analyze the effects of Chaco Serrano forest fragmentation on gall inducing species associated with four native plants species, simultaneously examining area and edge effects as well as the role of host plant availability on such effects. At edge and interior locations in each of nine forest sites in an area gradient in Central Argentina, we estimated herbivory as (1) the proportion of galled plants and (2) the number of galls per plant. Herbivory variations in relation to forest area and edge/interior locations were analyzed with generalized linear models, whereas the influence of plant availability in mediating area and edge effects was assessed by Structural Equation Models. Different responses to fragmentation were observed, depending on the insect species and also on the chosen herbivory indicator. Significant edge and area effects were detected in four and two out of ten performed models, respectively. When significant, edge effects were mostly positive and consistently direct rather than mediated by plant availability; instead, area effects varied from positive and led by plant abundance, to negative and independent of plant availability. Our study provides new evidence of a tendency for galling insects to benefit from edge conditions, while showing less consistent effects regarding forest size. Our results also suggest a very limited role for plant availability as a mechanism mediating fragmentation effects on herbivory by galling insects.     

Phytophagous insect-woody sprout interactions in tropical eucalypt forest. II. Insect community structure

Abstract Sucking insects constituted 79% of all phytophagous insects collected from woody sprouts in the ground layer of a tropical eucalypt forest. Mobile insect groups such as non-psyllid Hemiptera and Orthoptera were relatively frequent in this environment compared to temperate, Eucalyptus-dominated vegetation. The high fire frequency of the tropical eucalypt forest may favour mobile insect groups. The capture of sucking insects and caterpillars peaked in dry season samples. Other patterns of abundance of phytophagous insect groups showed little consistency in their seasonal trends between host species or between vegetation types within host species. Disparities between chewing insect abundance in daytime samples and the damage chewing insects cause, may result from disproportionate consumption by large, mainly nocturnal insects, such as members of the Orthoptera. In this study, 21% of insect species were specialists on single plant species. This study suggested that insect abundance reflected the growth patterns of woody sprouts after regular burning, rather than that plant growth and development were tuned to the pressures of insect herbivory.     

Insect Herbivores and Leaf Damage along Successional and Vertical Gradients in a Tropical Dry Forest

The availability and quality of resources for herbivores in tropical dry forests (TDFs) vary in time and space, affecting herbivore guilds differently across spatial scales (both horizontally and vertically), with consequences to the distribution of leaf damage in these forests. We attempted to elucidate the distribution patterns of herbivorous insect guilds and leaf damage throughout the secondary succession and vertical stratification along the rainy season in a Brazilian TDF. With the advance of the succession, a greater richness and abundance of herbivorous insects were found, resulting in higher leaf damage in intermediate and late stages. This pattern, however, was not observed for the frequency of leaf miners. At a smaller spatial scale, the host tree height positively affected the richness and abundance of insects. The higher leaf damage was found in canopy, which also harbored a greater richness and abundance of chewing herbivores compared to the understory at both the beginning and the end of the rainy season. Although for sap‐sucking insects, this was only true at the beginning of the season. We detected a decrease in insect richness and abundance at the end of the rainy season, probably due to a synchronization of insect activity with the availability of young, highly nutritious plant tissues. These results are consistent with other studies that found a general trend of increasing richness and abundance of herbivorous insects and leaf damage throughout the secondary succession (early to late stages) and between vertical strata (understory to canopy), suggesting that forest complexity positively affects herbivores.     

Spillover of tent caterpillar (Malacosoma americanum) herbivory onto willow bioenergy crops in an agricultural landscape

The circumstances and potential for insects to damage perennial bioenergy crops is not well understood in the United States. In this study, we evaluated the spillover and herbivory of eastern tent caterpillars (Malacosoma americanum) from host trees onto short rotation coppice (SRC) willow bioenergy crops (Salix sp.). Host trees were all in the Rosaceae family and included Prunus americana, Prunus virginiana and Malus sp. Willow showed greater leaf herbivory with increasing proximity to a defoliated host tree, suggesting that tent caterpillars spilled‐over to willow after denuding their host. More tent caterpillar herbivory was associated with greater mortality of willow. This study suggests that landscape context and spatial position of host trees is important to the early establishment of a willow bioenergy crop.     

Testing the host‐finding ability of a monophagous caterpillar in the field

1. Relatively few studies of the host‐finding ability of specialised, phytophagous insects involve direct observations of individual insects moving among intact hosts and non‐hosts. Information from such studies can inform the design of restoration programmes for species of conservation concern. 2. The movement of caterpillars of the threatened Oregon silverspot butterfly, Speyeria zerene hippolyta (Edwards) (Lepidoptera: Nymphalidae) was studied in the field in cleared arenas with 10 cm radii. Caterpillars were placed in the centre, surrounded by three individuals of their host, Viola adunca, and three different non‐host individuals, separated by bare ground. In a second experiment, second instars were placed between a host and a non‐host, 3–6 cm away. Caterpillars were observed to determine if they walked to their host more often than expected by chance. 3. Caterpillars walked to vegetation significantly more often than expected by chance. They did not, however, reach their hosts more often than expected, based on plant availability. 4. It is concluded that S. z. hippolyta caterpillars can distinguish vegetation from bare ground from 10 cm away. There is no evidence that they can distinguish their host plant from other herbaceous species at distances of 3 cm.     

Day vs. night predation on artificial caterpillars in primary rainforest habitats – an experimental approach

The influence of natural enemies has led to the evolution of various predator avoidance strategies in herbivorous insects. Many caterpillars are exclusively active at night and rest during the day. It is widely assumed that nocturnal activity in caterpillars reduces their risk of falling prey to their natural enemies. To test this hypothesis, we compared predation pressure between day and night in tree‐fall gaps and closed‐canopy forest sites in an Amazonian primary lowland rainforest. Artificial clay caterpillars, showing camouflaged colouration (green), were exposed as potential prey to a natural predator community. Attacks were significantly more frequent during daytime and were reduced by about a quarter at night in tree‐fall gaps, and by a third in closed‐canopy forest sites. This supports the idea of time‐dependent activity in caterpillars as an antipredatory adaptation. Further, independent of the time of day, predation pressure on caterpillars was significantly higher in tree‐fall gaps compared to closed‐canopy forest habitats. Nearly all predation events were caused by arthropods, whereas birds played a negligible role. Across both habitat types and time scales, ants acted as major predator group, emphasising their important role in population control of herbivorous insects in lowland rainforest ecosystems. This is the first experimental study using artificial caterpillars to examine whether time‐scheduling of exposition might influence predation risk amongst undefended, solitary, free‐living lepidopteran larvae.     

Temporal differences in food abundance promote coexistence between two congeneric passerines

Many related species share the same environment and utilize similar resources. This is surprising because based on the principle of competitive exclusion one would predict that the superior competitor would drive the other species to extinction; coexistence is only predicted if interspecific competition is weaker than intraspecific competition. Interspecific competition is frequently reduced by differential resource use, resulting in habitat segregation. In this paper, we use the closely related collared and pied flycatcher to assess the potential of habitat differences to affect interspecific competition through a different mechanism, namely by generating temporal differences in availability of similar food resources between the two species. We found that the tree species composition of the breeding territories of the two species differed, mainly by a higher abundance of coniferous species around nest-boxes occupied by pied flycatchers. The temporal availability of caterpillars was measured using frass traps under four deciduous and two coniferous tree species. Deciduous tree species showed an early and narrow peak in abundance, which contrasted with the steady increase in caterpillar abundance in the coniferous tree species through the season. We subsequently calculated the predicted total caterpillar biomass available in each flycatcher territory. This differed between the species, with biomass decreasing more slowly in pied flycatcher territories. Caterpillar biomass is strongly correlated with the reproductive success of collared flycatchers, but much less so with pied flycatchers. However, caterpillar availability can only partly explain the differences in seasonal decline of reproductive success between the two species; we discuss additional factors that may contribute to this species difference. Overall, our results are consistent with the suggestion that minor habitat differences between these two species may contribute to promoting their coexistence.     

Temporal variation in different life stages of moths (Lepidoptera) from a southwestern temperate forest of Korea: A preliminary study

Two study sites in a temperate forest in Mt. Seungdal-san, Muan, Jeonnam in southwestern Korea were selected for the collection of caterpillars and adult moths (Lepidoptera). Here, we determined (1) the characteristics of moth fauna based on lepidopteran larvae and adults, and (2) the differences in temporal variation between these two developmental stages. In addition, we investigated the life history of moth species collected at the surveyed sites. Of the 206 caterpillars collected, 17 moth species from 9 families were successfully reared. A total of 342 adult moth species and 2108 individuals from 15 families were collected. Twenty-two plants were identified as host plants of 188 caterpillars. Two tree species, Prunus serrulata var. spontanea and Quercus serrata, were widely distributed in the study sites. Leaf water content (%) of Quercus serrata and Carpinus laxiflorawas the highest in June, whereas the leaf water content of Platycarya strobilacea was the highest in August. We postulated that many of the variables in the temperate forest, such as host plant availability, parasitoids, disease, and weather, affected the lepidopteran caterpillar populations. There were differences in species composition among the sampling methods which suggest the need for diverse methods to uncover total biodiversity. However, it should be noted that a long term and well-planned study with efficient rearing of caterpillars is needed to better understand these correlations.     

Insect herbivores foraging on seedlings in an unlogged rain forest in Guyana: spatial and temporal considerations

About 9,000 individuals of sap-sucking and leaf-chewing insects, representing 345 species, were collected from 10,000 seedlings belonging to 5 rainforest tree species in an unlogged forest in Guyana. For the 40 most common species, it was possible to estimate their host specificity, diurnal activity, seasonal distribution, spatial aggregation, abundance and body weight. Most species were generalists but more specialised species tended to show a higher spatial aggregation, a more restricted diurnal activity and a higher seasonality. Although insect abundance was highest at the onset of the long wet season in May, seasonal amplitude was not pronounced. The combined effects of host and rainfall explained 14.5% of the total variance in insect seasonality, which was poorly explained by the leaf production of seedlings. The spatial distribution of insects was often aggregated and, overall, explained by host effect, production of young foliage, number of conspecific trees within a radius of 50m, and number of dead seedlings at each collecting station. However, these variables explained only 7% of the variance in spatial distribution. The lack of notable influence of leaf production and other important variables recorded at the collecting stations suggests that the seedlings represent a marginal food resource for most of the insect species collected.     

Resource predictability and specialization in avian malaria parasites

We tested the hypothesis that avian haemosporidian (malaria) parasites specialize on hosts that can be characterized as predictable resources at a site in Amazonian Ecuador. We incorporated host phylogenetic relationship and relative abundance in assessing parasite specialization, and we examined associations between parasite specialization and three host characteristics – abundance, mass and longevity – using quantile regression, phylogenetic logistic regression and t‐tests. Hosts of specialist malaria parasite lineages were on average more abundant than hosts of generalist parasite lineages, but the relationship between host abundance and parasite specialization was not consistent across analyses. We also found support for a positive association between parasite specialization and host longevity, but this also was not consistent across analyses. Nonetheless, our findings suggest that the predictability of a host resource may play a role in the evolution of specialization. However, we also discuss two alternative explanations to the resource predictability hypothesis for specialization: (i) that interspecific interactions among the parasites themselves might constrain some parasites to a specialist strategy, and (ii) that frequent encounters with multiple host species, mediated by blood‐sucking insects, might promote generalization within this system.