AbstractAlthough studies of insect decline have recently dominated headlines worldwide, their interpretation requires caution since for most species, we lack long‐term population baselines. In the tropics, where most insect species thrive, our knowledge is even more limited and so reliable insect assessments must originate from well‐established long‐term monitoring efforts. Combining the extensive monitoring data from the Arthropod Program of the Smithsonian Tropical Research Institute (STRI) on Barro Colorado Island (BCI), Panama, we compare whether known arthropod diversity can be detected through metabarcoding of bulk insect samples obtained through automatic light‐trapping. Our study detected 4402 species based on Barcode Index Numbers (BIN) and detected fine‐scale differences between wet and dry seasons and sampling localities. We further refined our analysis to indicate which families and genera explained seasonal turnover. Using samples collected in parallel, but sorted manually as part of the ongoing arthropod monitoring program, we compared these methods. Out of 538 BINs recovered through manual sorting, there was a 70% overlap with the metabarcoding data; however, it represented 30% of the total BINs detected through metabarcoding. Expecting higher detection through metabarcoding, we also compare the results with the 14 years of sampling in BCI to better understand how well the monitoring program has captured the diversity of focal groups. Our results revealed a ~50% overlap between both methods and similar total catch. Barcode Index Numbers manually detected but not recovered by metabarcoding highlight some of the limitations of molecular detection methods such as primer bias. Contrastingly, BINs detected with metabarcoding, but not recovered by the traditional monitoring scheme, highlight the importance of local and regional barcode reference libraries.

The population dynamics of most tropical insects are unknown and long‐term monitoring programmes are urgently needed to evaluate a possible insect decline in the tropics. In this context, functional groups can be used effectively to summarise time‐series for species‐rich taxa. Neotropical dung beetles have often been catalogued into functional groups, but close relatives also of ecological significance, the Dynastinae, are awaiting such a classification. Here, we examine the functional groups of Dynastinae at the regional (Panama: 147 species) and local (Barro Colorado Island, BCI: 56 species) scales. Our optimum classification of Panamanian species distinguished five groups, one of which is probably artificial and accounts for species ecologically poorly known. Ecological attributes or species traits mainly influencing the delineation of groups were geographical distribution, body length, seasonal aggregation, larval food and whether the adult may be present in decaying wood. Our analyses indicated that (1) missing trait values and the high percentage of ‘cryptic’ species (25%) influenced the delineation of groups; (2) the dendrogram similarity of functional groups versus phylogenetic tree was low, although some traits were phylogenetically conserved; and (3) the overall structure of functional groups was conserved when comparing regional and local data, suggesting no drastic loss of functional groups locally. To proceed with the functional classification of poorly known tropical insects, we recommend a cautious selection of traits a priori, inclusion of ‘cryptic’ species recognised by DNA barcoding, and building phylogenies, which may allow a careful taxonomic imputation to complete species‐traits matrices.

In the tropics, antagonistic seed predation networks may have different properties than mutualistic pollination and seed dispersal networks, but the former have been considerably less studied. We tested whether the structure of antagonistic tripartite networks composed of host plants, insects developing within seeds and fruits, and their insect parasitoids could be predicted from plant phylogenetic distance and plant traits. We considered subsets of the networks ('subnetworks') at three rainforest locations (Panama, Thailand, Papua New Guinea), based on insect families, plant families or plant functional groups. We recorded 3197 interactions and observed a low percentage of realized interactions, especially in Panama, where insect host specificity was higher than in Thailand or New Guinea. Several factors may explain this, including insect faunal composition, incidence of dry fruits, high fruit production and high occurrence of Fabaceae at the Panamanian site. Host specificity was greater among seed-eaters than pulp-eaters and for insects feeding on dry fruits as opposed to insects feeding on fleshy fruits. Plant species richness within plant families did not influence insect host specificity, but site characteristics may be important in this regard. Most subnetworks were extremely specialized, such as those including Tortricidae and Bruchinae in Panama. Plant phylogenetic distance, plant basal area and plant traits (fruit length, number of seeds per fruit) had important effects on several network statistics in regressions weighted by sampling effort. A path analysis revealed a weak direct influence of plant phylogenetic distance on parasitoid richness, indicating limited support for the 'nasty host hypothesis'. Our study emphasizes the duality between seed dispersal and seed predation networks in the tropics, as key plant species differ and host specificity tends to be low in the former and higher in the latter. This underlines the need to study both types of networks for sound practices of forest regeneration and conservation.

Insect seed predators are important agents of mortality for tropical trees, but little is known about the impact of these herbivores in rainforests. During 3 years at Khao Chong (KHC) in southern Thailand we reared 17,555 insects from 343.2 kg or 39,252 seeds/fruits representing 357 liana and tree species. A commented list of the 243 insect species identified is provided, with details about their host plants. We observed the following. (i) Approximately 43% of identified species can be considered pests. Most were seed eaters, particularly on dry fruits. (ii) Approximately 19% of parasitoid species (all Opiinae) for which we could determine whether their primary insect host was a pest or not (all Bactrocera spp. breeding in fruits) can be considered beneficials. (iii) The seeds/fruits of approximately 28% of the plant species in this forest were free of attack. Phyllanthaceae, Rubiaceae and Meliaceae were attacked relatively infrequently; in contrast, Annonaceae, Fabaceae, Sapindaceae and Myristicaceae were more heavily attacked. There was no apparent effect of plant phylogeny on rates of attack but heavily attacked tree species had larger basal area in the KHC plot than rarely attacked tree species. (iv) Insects reared from fleshy fruits were more likely to show relatively stable populations compared to insects reared from dry fruits, but this was not true of insects reared from dipterocarps, which appeared to have relatively stable populations throughout the study period. We tentatively conclude that insects feeding on seeds and fruits have little effect on observed levels of host abundance in this forest.

A significant proportion of the mortality of rainforest trees occurs during early life stages (seeds and seedlings), but mortality agents are often elusive. Our study investigated the role of herbivorous insects and pathogens in the early regeneration dynamics of Guazuma ulmifolia (Malvaceae), an important tree species in agroforestry in Central America. We reared pre-dispersal insect seed predators from G. ulmifolia seeds in Panama. We also carried out an experiment, controlling insects and pathogens using insecticide and/or fungicide treatments, as well as seed density, and compared survivorship of G. ulmifolia seeds and seedlings among treatments and relative to untreated control plots. We observed (1) high pre-dispersal attack (92%) of the fruits of G. ulmifolia, mostly by anobiine and bruchine beetles; (2) negligible post-dispersal attack of isolated seeds by insects and pathogens; (3) slow growth and high mortality (> 95%) of seedlings after 14 weeks; (4) low insect damage on seedlings; and (5) a strong positive correlation between seedling mortality and rainfall. We conclude that for G. ulmifolia at our study site the pre-dispersal seed stage is by far the most sensitive stage to insects and that their influence on seedling mortality appears to be slight as compared to that of inclement weather. Thus, the regeneration of this important tree species may depend on effective primary dispersal of seeds by vertebrates (before most of the seed crop is lost to insects), conditioned by suitable conditions in which the seedlings can grow.

In 1987, in the first issue of Conservation Biology, Edward O. Wilson wrote about the "little things that run the world" – the importance and conservation of insects (Wilson, 1987). Readers of Insect Conservation and Diversity will no doubt be very familiar with the concept. Sadly, however, this perception is not as widely shared among the rest of the scientific community as it should be, and insects are still comparatively neglected as a prime focus of scientific investigations. For instance, if we look at the Thompson-Reuter impact factors (IF) of specialised scientific journals for 2017 (http://jcr.incites.thomsonreuters.com/JCRJournalHomeAction.action?year=&edition=&journal=#), the highest ranked journal dedicated to entomology, Annual Review of Entomology (IF = 13.860), is ranked 139th out of 122 271 journals. In comparison, our botanical colleagues fare somewhat better, with the highest ranked journal in plant sciences, Annual Review of Plant Biology (IF = 18.172), ranked 83rd overall. Insect Conservation and Diversity continues to be among the top journals in entomology (IF = 2.091; ranked 14th), but overall is ranked 4549th among the journals evaluated by Thompson-Reuter. There is certainly room for improvement, of course, but in general this reflects the large difference in the scale of endeavour across different scientific disciplines. Part of this challenge may be related to an imbalance in the ratio of funding afforded to invertebrate studies (Leather, 2009). We entomologists are acutely aware of inherent biases in conservation research. Vertebrate studies dominate the field (69% of papers versus 3% of described species) while invertebrate studies lag far behind (11% of papers versus 79% of species: Clark & May, 2002). This taxonomic chauvinism has been commented on and lamented upon many times (e.g. Leather, 2009 and references therein), including in one of our previous editorials (Leather et al., 2008). Moreover, current trends show no signs of improvement (Titley et al., 2017), and the imbalance against insect studies is becoming even more pronounced in tropical countries (Titley et al., 2017), where recent estimates suggest over 25 000 arthropod species occurring in just a few hectares of tropical rainforest (Basset et al., 2012). But these issues may not even be the most serious cause for concern. We argue here that the neglect of insects as study organisms has led to serious bias in our understanding of the functional ecology of ecosystems. In other words, ignorance of the identity and role of insects in ecosystems may seriously impede conclusions related to the true contribution that insects make to ecosystem functionality (Weisser & Siemann, 2008). We may be able to estimate indirectly the role of insects in ecological processes, but without a good knowledge of the identity and life history of the species responsible for these processes, our conclusions may be rather subjective. "Knowing the players" is therefore crucial for sound studies of the effects of insects on ecosystem functioning (Schmitz, 2008). This situation is particularly obvious in studies of insect-plant interactions (or should we say in this instance "plant-insect interactions"?), which represent a significant field of ecological research in its own right (Calatayud et al., 2018). Many plant science researchers in this field simply seem to ignore the identity and diversity of the types of insect species doing the work. For instance, given the difficulty in evaluating damage caused by sap-sucking insects, most studies of herbivory (leaf damage) only focus on the action of leaf-chewing insects. This is very evident in studies on herbivory carried out in tropical forests (e.g. Coley & Barone, 1996). Nevertheless, detailed studies have shown that the occurrence of sap-sucking insects on rainforest plants is by no means trivial (Novotny & Basset, 1998; Dem et al., 2013). Since these insects can be vectors of important plant diseases (Denno & Perfect, 2012), they could have a significant effect on rates of mortality of their hosts. In addition, most of the "plant-insect" literature has focused on insects feeding on leaves. Much less is known about the identities and roles of insects attacking other plant parts (e.g., flowers, fruits, roots, stems). Another important issue is the estimation of herbivory caused by leaf-chewing insects in tropical rainforests. Botanists have been keen to measure the area of holes in leaves (review in Coley & Barone, 1996) but few, if any, discuss the interpretation of their findings with regard to the identities and life histories of the main species responsible for leaf damage. Total leaf damage rates are often assumed to be correlated with insect species richness, abundance or biomass (e.g., Coley, 1983, discussing the spatial distribution of herbivory). The handful of studies that have, however, considered insect identity and associated variables (abundance, species richness, biomass) all concluded that leaf damage is likely to depend on the feeding behaviour of a few dominant leaf-chewing species and this may complicate the interpretation of results obtained in herbivory studies focusing on community-level patterns (e.g., Marquis, 1991; Basset & Höft, 1994). We know that the major impact of herbivores on plants, particularly in rainforests, is driven by relatively few insect species, because most of the rest are relatively rare and their action restricted in time (Owen, 1983; Bernays & Graham, 1988). Thus, while overall herbivory rates may be an important correlate of plant fitness, it gives us few clues about the distribution and feeding preferences of the species responsible for the leaf damage. In this essay, we briefly explore the implications of ignoring the identity and traits of insects in the context of another research topic popular among our botanical colleagues, the Janzen–Connell hypothesis, JCH (Janzen, 1970; Connell, 1971). The JCH proposes an explanation for the coexistence of tree species in diverse tropical forests. Seeds are most likely to disperse to sites close to their parent trees, but this is also where they are likely to be most frequently attacked by host-specific enemies such as insects and pathogens that might aggregate near the parent trees. By contrast, seeds and seedlings that do manage to disperse further away from the parent tree are more likely to survive due to escape from enemies. In other words, conspecific negative density-dependent survival results from the proliferation of species-specific herbivores and pathogens on hosts in areas of high conspecific plant densities, giving a negative correlation between relative pest attack rate and distance from parent trees to their nearby offspring (Janzen, 1970; Connell, 1971; Comita et al., 2010; Bagchi et al., 2014). In the seminal paper by Janzen (1970), few examples of insect species responsible for negative density dependence among rainforest plants are provided, but this information may be gathered from subsequent papers, along with more recent studies (Table 1). Most of the studies concerned with Janzen–Connell effects pay little attention to the identity of insects potentially able to induce such effects (reviews in Clark & Clark, 1984; Hammond & Brown, 1998; Carson et al., 2008; Comita et al., 2014: 63 studies considered). The compilation in Table 1 indicates that most studies that have assessed the role of specific insect species in causing patterns consistent with the predictions of the JCH were performed in the Neotropics (only one study originated from the Old World tropics), in rather open forests, savanna or even open pastures, targeted seeds over seedlings, often included palm or leguminous trees (64% of cases) and the main species responsible for Janzen–Connell effects were often bruchine beetles. One might be tempted to think that many of these study systems were perhaps selected for the ease of studying large seed crops attacked by noticeable seed predators. What is clear, is that more studies targeting closed tall forests, and trees from other plant families and their seedlings are urgently needed before we can make sweeping conclusions about the generality of Janzen–Connell effects induced specifically by insects. Another bias that is obvious from the studies listed in Table 1 is the almost exclusive focus on chewing insects attacking either seeds or seedlings. The only exception is an influential paper by Janzen in which he reports on the effects of an external-feeding sap-sucking bug on seeds of Sterculia apetala (Janzen, 1972a). Seed bugs (Lygaeidae and related families) are renowned as potentially important seed predators in the tropics (Slater, 1972 and references therein). Hence, it is also clear that if we are serious about evaluating potential Janzen–Connell effects induced by insects, it is imperative to pay more attention to the guild of externally seed- and fruit-sucking insects in rainforests. Janzen's study on seed mortality by seed-sucking bugs on Sterculia apetala also illustrates another potentially important point. Since the externally sap-sucking bug studied by Janzen may transmit a pathogenic fungus to the host tree (Janzen, 1972a), the ultimate cause of seed mortality might appear to be caused by a seed pathogen rather than by an insect. This illustrates the need to consider the synergy between insects and pathogens. As discussed by Carson et al. (2008), the JCH is ultimately a plant community-level hypothesis, but all the studies reported in Table 1 targeted a single plant species. While research within the framework of the JCH has mostly been conducted on enemies that attack seeds and seedlings that have already dispersed from the mother plant, Janzen (1970) also suggested that coexistence of plant species in tropical forests could also be promoted by pre-dispersal seed enemies (i.e., enemies attacking developing or mature seeds in the canopy). Gripenberg (2018), in stressing the need to pay attention to attack by pre-dispersal seed enemies, reviewed the studies that have assessed the pattern of insect seed predation in tropical forest plant communities. To date, this includes only 15 studies world-wide, from which just two thirds provide hard data about insects. Again, currently available data are so limited that we lack the necessary insect background to discuss adequately the contribution of insects to Janzen–Connell effects in tropical rainforests. What can we gain from knowing the identity and ecology of insects in studies of negative-density dependence in tropical rainforests? Primarily this includes information on patterns of host use (specificity) by specific insect species; information on whether the same insect species tend to feed on adult foliage and seedlings; and spatial patterns of foraging by insects. To address some of these issues briefly, we need to consider the separate effects of insects feeding on seeds versus seedlings. We know that most insects attacking seeds in rainforests are highly host specific (Janzen, 1980; Ctvrtecka et al., 2014; Gripenberg, 2018), in accordance with the expectations of the JCH. What is less well known is the degree of spatial contagion of seed predators near parent trees, which may depend on the ecology of species considered. For example, Janzen (1975b) reported that two species of bruchine beetles are host specific to the seeds of Guazuma ulmifolia in Costa Rica, with one being a pre-dispersal seed predator attacking the seeds on the tree, while the other exclusively attacks the mature seeds after they have fallen to the ground. Hence, the identity and ecology of insect species is crucial to fully understand patterns of pre- and post-dispersal seed attack and any resulting effects on plant fitness and patterns of recruitment. Even if the assumptions of host specificity and contagion near the parent trees are met, this does not imply that Janzen–Connell effects related to seeds may be pervasive. Insects need to subsist at minimum densities on their hosts in order to induce significant plant mortality. For example, in the forests of New Guinea 95% of the woody plant species sampled for seed-eating weevil and lepidopteran assemblages had low rates of seed infestation (Ctvrtecka et al., 2014; Sam et al., 2017). Here, a recognition of the main insect species and estimation of their infestation rates in seeds are needed before assessing possible Janzen–Connell effects induced by insects. Overlooking even the higher taxa of insects responsible for seed damage may lead to ambiguous interpretation of results. For example, Bruchinae are often host-specific on seeds of Fabaceae in the Neotropics (Janzen, 1980), whereas they are almost totally replaced by several less host-specific weevil subfamilies in the Old World (Ctvrtecka et al., 2014; Basset et al., 2018). The potential for Bruchinae to induce Janzen–Connell on their fabaceaous hosts is thus much higher than for weevils of the Old World, as suggested by Table 1. Furthermore, botanists pay considerable attention to plant phylogeny in studies of JCH, but they should also take note of plant traits that may explain oviposition patterns of insects attacking seeds, which are not necessarily related to plant phylogeny. One of the most important traits in this regard may be the degree of fleshiness of the fruit (Sam et al., 2017; Basset et al., 2018; C. Dahl et al., unpubl. data). When assessing the contributions of insects to Janzen–Connell effects, it is also important to have good insights into the feeding ecology of different taxa. Even in relatively well-known Lepidoptera, it can be difficult to separate the seed predator species from pulp eaters or scavengers. Several taxa that are often considered to be scavengers also contain lineages with other life history strategies, such as in the Tineidae (Robinson, 2009), so precise identification of insects reared from seeds or fruits is crucial. If we now turn our attention to seedlings, there are very few community-wide studies of insect herbivores attacking seedlings in tropical rainforests. Twenty years ago, one study in Guyana concluded that free living species attacking seedlings persisted at very low densities, were often generalists, and that Janzen–Connell effects mediated by insects feeding on seedlings were, consequently, unlikely to exist in the system studied (Basset, 1999). We now know that the lack of host specificity (particularly for insects feeding on seedlings) does not necessarily invalidate their potential contribution to plant species coexistence, as negative density dependence may also be generated by the action of generalist herbivores if they tend to be attracted to areas of high conspecific plant density (Lewis & Gripenberg, 2008). Regarding contagion from parent trees, we have noted that insect species responsible for Janzen–Connell effects were often studied in rather open forest or pastures (Table 1), and less so in closed tall forests. In fact, in these forests, where presumably Janzen–Connell effects induce high local diversity of trees (Janzen, 1970; Connell, 1971), contagion of insect herbivores from the parent trees to seedlings has rarely been demonstrated. This may be because the biotic and abiotic conditions experienced in the canopy versus understorey of forests are strikingly different, resulting in different suites of free-living herbivores attacking plants in these two strata. These differences have been observed both at the level of host plant species (e.g., Basset, 2001) and the plant community as a whole (Basset et al., 2015). There may of course be exceptions and they are more likely to involve endophagous insects (stem borers, gallers, miners) than ectophagous insects, because external conditions induced by the forest strata may be buffered to some extent by microclimatic conditions inside the host tissues. Nevertheless, the proportion of host tree species studied that supported the same insect species of either gallers or miners in both the canopy and understorey in one Panamanian wet forest was low and amounted to only 6% (out of 18 species: Medianero et al., 2003). Under these conditions, contagion of insect herbivores from parent trees to seedlings is likely to be rather uncommon in closed tall rainforests. Despite claims that in some instances signs of leaf damage can be unequivocally assigned to particular insect species (Barone, 2000; Downey et al., 2018), in our experience it is nearly impossible to do so for the vast majority of the diverse insect species feeding on the leaves of tropical trees and seedlings, particularly in the case of generalist species. This greatly impedes our ability to investigate the causal mechanisms of negative density dependence in seedlings of tropical rainforests. Moreover, one recent study suggested that the amount and categories of herbivore damage on rainforest seedlings may even differ between continents. For example, the percentage of damage on seedlings that could be assigned to insects represented 56%, 78%, and 85% of observations in rainforests in Panama, Thailand, and Papua New Guinea, respectively (Y. Basset et al., unpubl. data). Identifying the main herbivore species responsible for such variation in herbivory (at least leaf-chewing herbivory) is crucial. And, of course, the degree to which seedlings of different plant species can tolerate differing levels of herbivory before Janzen–Connell effects are triggered is an open question. If we do entertain the idea that at least some insect species are responsible for some examples of negative-density dependence observed in rainforests (review in Comita et al., 2010), then which taxa are most likely to be responsible for these effects? If we consider post-dispersal attack of seeds fallen on the ground, then highly host-specific Bruchinae (Janzen, 1980) and perhaps certain Curculionidae (Pinzón-Navarro et al., 2010) may fit the bill, although many species may only be involved in pre-dispersal attack. We should also not underestimate ants as seed removers in rainforests (Ruzi et al., 2017), and therefore as possible engineers of Janzen–Connell effects. Insect herbivores attacking seedlings in rainforests involve many taxa (Basset & Charles, 2000). Leaf-chewing insects are often represented by Chrysomelidae, leaf-feeding weevils (Entiminae), but Lepidoptera larvae are relatively rare on seedlings (e.g., 6% of the total insect individuals collected in Basset & Charles, 2000). Orthoptera and Phasmatodea are also rather infrequent, at least during day-time censuses (Basset & Charles, 2000). The low incidence of most of these insects on seedlings (Basset, 1999) makes them unlikely candidates to successfully induce Janzen–Connell effects, but exceptions may exist. Further cases of insects notoriously dangerous for the survival of seedlings are worth discussing briefly. First, the action of potential vectors of phytopathogens needs to be quantified and understood. This includes, for example, xylem-feeding and generalist Cicadellinae, which are common as nymphs and adults in the understorey of tropical rainforests, and are able to transmit phytopathogenic viruses (Nielson, 1968). Additionally, this may involve adult weevils (for example Conotrachelus spp.) or bark beetles, which attack seeds at the larval stage and perform maturation feeding on seedlings as adults (Basset & Charles, 2000). In this situation, they may transmit pathogenic fungi, as for example in the case of Dutch elm disease (Martín et al., 2018). Second, insects damaging meristems may be particularly threatening, such as one erebid moth decapitating seedlings in Costa Rica (Janzen, 1971b). In Panama, this category of damage represents nearly 20% of all observations of seedlings damaged in a community study (Y. Basset et al., unpubl. data). Lepidopterous stem borers may also damage meristems but this group is far less diverse than free-feeding caterpillars, so it may be relatively easy to quantify their effects on particular host species (e.g., Sullivan, 2003). Last, insects able to completely defoliate seedlings are also of concern. This may include outbreaks of host-specific Lepidoptera (Barone, 2000), but this situation is rather rare in tropical rainforests. Large generalist caterpillars such as Saturniidae (Hartnett et al., 2012) may be worth investigating in this context. In conclusion, Janzen–Connell effects mediated by insects in tropical rainforests appear to be less likely by contagion of host-specific species from parent trees to seedlings, but more likely via a combination of escape of seeds from pre-dispersal attack (Lawson et al., 2012), and attack of seedlings by generalist herbivores in the forest understorey, possibly aggravated by transmission of diseases by insect vectors. To collect and identify the culprits of damage is challenging, particularly on seedlings, because generalists may subsist at low densities (Basset, 1999) or specialists may have elusive behaviours. For example, Janzen (1971b), estimated that on average just 10 minutes were necessary for an erebid moth to decapitate one seedling before walking off, rendering any direct census of caterpillars in this study system very difficult. Elegant experiments with insecticide or exclusion of insect herbivores may help us to quantify the action of insect herbivores more effectively (e.g., Bagchi et al., 2014) and those results should be coupled with good old-fashioned natural history observations, or with observations acquired with new technologies. For example, the metabarcoding of the gut of potential insect herbivores (e.g., García-Robledo et al., 2013) or automatic detection of insect activity (e.g., Reynolds & Riley, 2002) on seedlings, particularly at night, appear to be promising opportunities in this context. Further, such studies may be performed at locations where extensive vegetation data, including the basal area, spatial location, and seed production of parent trees, may be available, such as in the ForestGEO network of permanent forest plots (Anderson-Teixeira et al., 2015; Basset et al., 2018). New tools, such as DNA barcoding, are now available to assist with rapid and accurate identification of insect species (Miller, 2014), including the BIN clustering algorithm and interim nomenclature system, which facilitates forming putative species concepts and communicating about them (Schindel & Miller, 2010; Ratnasingham & Hebert, 2013). We hope that we may have convinced our non-entomologist readers, perhaps curious about the title of this essay, of the value of paying attention to the identity of insects potentially responsible for Janzen–Connell effects in rainforests, and, to this effect, to collaborate with entomologists. Hopefully, some of our regular readers may also see better scope for collaboration with botanists or forest ecologists regarding this fascinating topic. The ideas advanced in this essay were shaped by a project supported by the Czech Science Foundation (GAČR 16-20825S) and a grant from the US National Science Foundation (DEB 0841885).

We propose a new classification of rain forest plants into eight fruit syndromes, based on fruit morphology and other traits relevant to fruit-feeding insects. This classification is compared with other systems based on plant morphology or traits relevant to vertebrate fruit dispersers. Our syndromes are based on fruits sampled from 1,192 plant species at three Forest Global Earth Observatory plots: Barro Colorado Island (Panama), Khao Chong (Thailand), and Wanang (Papua New Guinea). The three plots differed widely in fruit syndrome composition. Plant species with fleshy, indehiscent fruits containing multiple seeds were important at all three sites. However, in Panama, a high proportion of species had dry fruits, while in New Guinea and Thailand, species with fleshy drupes and thin mesocarps were dominant. Species with dry, winged seeds that do not develop as capsules were important in Thailand, reflecting the local importance of Dipterocarpaceae. These differences can also determine differences among frugivorous insect communities. Fruit syndromes and colors were phylogenetically flexible traits at the scale studied, as only three of the eight seed syndromes, and one of the 10 colors, showed significant phylogenetic clustering at either genus or family levels. Plant phylogeny was, however, the most important factor explaining differences in overall fruit syndrome composition among individual plant families or genera across the three study sites.

Aim: Insects feeding on seeds and fruits represent interesting study systems, potentially able to lower the fitness of their host plants. In addition to true seed eaters, a suite of insects feed on the fleshy parts of fruits. We examined the likelihood of community convergence in whole insect assemblages attacking seeds/fruits in three tropical rain forests. Location: Three ForestGEO permanent forest plots within different biogeographical regions: Barro Colorado Island (Panama), Khao Chong (Thailand) and Wanang (Papua New Guinea). Methods: We surveyed 1,186 plant species and reared 1.1 ton of seeds/fruits that yielded 80,600 insects representing at least 1,678 species. We assigned seeds/fruits to predation syndromes on the basis of plant traits relevant to insects, seed/fruit appearance and mesocarp thickness. Results: We observed large differences in insect faunal composition, species richness and guild structure between our three study sites. We hypothesize that the high species richness of insect feeding on seeds/fruits in Panama may result from a conjunction of low plant species richness and high availability of dry fruits. Insect assemblages were weakly influenced by seed predation syndromes, both at the local and regional scale, and the effect of host phylogeny varied also among sites. At the driest site (Panama), the probability of seeds of a plant species being attacked depended more on seed availability than on the measured seed traits of that plant species. However, when seeds were attacked, plant traits shaping insect assemblages were difficult to identify and not related to seed availability. Main conclusions: We observed only weak evidence of community convergence at the intercontinental scale among these assemblages. Our study suggests that seed eaters may be most commonly associated with dry fruits at relatively dry tropical sites where fleshy fruits may be less prevalent.

During an investigation of the insect food web in Papua New Guinea several specimens of a new genus and species of large, black and orange braconine braconid wasp were reared from fruits of Rubiaceae. These are described here as Karposibracon papuensis Quicke & Butcher gen. et sp. nov. Karposibracon gen. nov. appears to belong to the tribe Braconini and is the largest known species in this group, with body length up to 12 mm. The new genus is illustrated photographically, distinguished from other genera, and comments are on its likely biology provided.

We studied a community of frugivorous Lepidoptera in the lowland rainforest of Papua New Guinea. Rearing revealed 122 species represented by 1,720 individuals from 326 woody plant species. Only fruits from 52% (171) of the plant species sampled were attacked. On average, Lepidoptera were reared from 1 in 89 fruits and a kilogram of fruit was attacked by 1.01 individuals. Host specificity of Lepidoptera was notably low: 69% (33) of species attacked plants from >1 family, 8% (4) fed on single family, 6% (3) on single genus and 17% (8) were monophagous. The average kilogram of fruits was infested by 0.81 individual from generalist species (defined here as feeding on >1 plant genus) and 0.07 individual from specialist species (feeding on a single host or congeneric hosts). Lepidoptera preferred smaller fruits with both smaller mesocarp and seeds. Large-seeded fruits with thin mesocarp tended to host specialist species whereas those with thick, fleshy mesocarp were often infested with both specialist and generalist species. The very low incidence of seed damage suggests that pre-dispersal seed predation by Lepidoptera does not play a major role in regulating plant populations via density-dependent mortality processes outlined by the Janzen-Connell hypothesis.

A community of frugivorous insects was studied by rearing of 25 565 individual insects representing three orders (Coleoptera, Lepidoptera and Diptera except Drosophilidae) from 326 woody plant species in a lowland rainforest in Papua New Guinea. Fruits from 19.3% of plant species were not attacked by any insect order, 33.4% of plant species were attacked by a single order, 30% by two orders and 17.2% by all three orders. The likelihood of attack by individual orders was positively correlated so that a higher proportion of plant species than expected suffered either no attack at all or was attacked by all three insect orders. Fruits from most of the plant species exhibited low rates of attack and low densities of insects. One kilogram of fruit was attacked on average by 11 insects, including three to four Coleoptera, six Diptera and one Lepidoptera. Thus, we reared on average one insect from 10 fruits, including one Diptera from 14 fruits, one Coleoptera from 22 fruits and one Lepidoptera from 100 fruits. Only 72 out of the 326 plant species hosted more than one insect per 10 fruits, and only seven species supported a density of greater than one insect per fruit. Our results suggest that specialized insect seed predators are probably too rare to maintain the diversity of vegetation by density-dependent mortality of seeds as suggested by the Janzen–Connell hypothesis. Fruit weight, fruit volume, mesocarp volume, seed volume and fleshiness had no significant effect on the probability that a fruit would be attacked by an insect frugivore. However, fruits attacked by Diptera were significantly larger and had larger volume of both mesocarp and seeds than fruits attacked by Coleoptera and Lepidoptera.

Abstract:A community of frugivorous weevils was studied by quantitative rearing of 57 weevil species represented by 10485 individuals from 326 woody plant species in lowland rain forest in Papua New Guinea. Only fruits from 35% of plant species were attacked by weevils. On average, weevils were reared from only 1 in 33 fruits and 1 kg of fruit was attacked by 2.51 individuals. Weevil host specificity was relatively high: 42% of weevil species fed on a single plant genus, 19% on a single plant family and only 16% were reared from more than one family. However, monophagous specialists represented only 23% of all reared individuals. The average 1 kg of fruits was infested by 1.84 individuals of generalist weevils (feeding on allogeneric or allofamilial host species), 0.52 individual of specialists (feeding on a single or several congeneric species), and 0.15 individual of unknown host specificity. Large-seeded fruits with thin mesocarp tended to host specialist species whereas those with thick, fleshy mesocarp were often infested with both specialists and generalists. Weevils tended to avoid small-seeded, fleshy fruits. The low incidence of seed damage (3% of seeds) suggests that weevils are unlikely to play a major role in regulating plant populations via density-dependent mortality processes outlined by the Janzen–Connell hypothesis.

The post-hibernating adults of the apple blossom weevil, Anthonomus pomorum (L.), show preferences for certain cultivars in mixed apple tree orchards. The degree of infestation of various cultivars was positively correlated with the density of flower buds at a comparable phenological stage, but the numbers of collected beetles were not linearly proportional to the bud density of different cultivars. Hence other possible factors, namely chemical ones, were investigated. Chromatographic analysis of apple tree bud emanations showed that volatiles from two different apple cultivars that show a different attractiveness to the beetles, differed in chemical composition. Several less volatile components of the bud emanation bouquet elicited antennographic responses in both male and female antennae. Four terpene hydrocarbons, namely 3-carene, perillene, caryophyllene and (E,E)-alpha-farnesene, were identified among the components that produced distinct electrophysiological responses in the antennae. These findings support a hypothesis that the adult weevils use chemical cues for olfactory discrimination during host-searching behaviour.

A possibility of using synthetic analogues of juvenile hormone (juvenoids) to disrupt imaginal diapause of the apple blossom weevil, Anthonomus pomorum females was demonstrated. Out of three preparations tested (methoprene, fenoxycarb and W-328) methoprene and fenoxycarb appeared to be effective. Sensitivity to juvenile hormone analogues develops early after imaginal emergence (even before the female starts to feed) and lasts throughout the whole aestivo-hibernation dormancy. Although the juvenoids could stimulate the onset of oogenesis at any time during diapause, the propensity of the ovaries to form normal eggs developed only during hibernation part of the dormancy; in earlier stages of diapause accumulation of yolk was observed but matured eggs were not produced. Methoprene treatment caused marked increase of locomotory activity accompanied with decrease of dry weight, increase of water content, depletion of trehalose resources, decrease of cold hardiness and, finally, 100% mortality within four weeks in the weevils treated during their feeding or aestivation stages. Although similar changes were observed in the treated pre-feeding weevils, they later recovered and survived until next spring without apparent loss of cold hardiness. A possibility of designing a control method based on this principle is discussed and the results of small-scale field trials that support its plausibility are reported.

The apple blossom weevil (Anthonomus pomorum) is a univoltine species with a reproductive diapause in both sexes that covers both aestivation and hibernation periods. It is manifested by the lack of mating behaviour and the arrest of gonadal development. The diapause in females can be terminated after exposure to field conditions by transferring the weevils to warm environment. The photoperiods tested (18L:6D and 12L:12D) had no apparent effect on speed and degree of diapause and postdiapause development, but availability of suitable food (sprouting apple tree buds) was a necessary prerequisite for initiation of gonadal development in the females. Under laboratory conditions the females became receptive and mated immediately after initiation of ovarian development, rather than after a prolonged feeding and egg maturation period as observed earlier in the field. Males acquire sexual maturity earlier than females, and initiation of their postdiapause development does not require food intake.