The extraordinary abundance of ants in tropical rainforest canopies has led to speculation that numerous arboreal ant taxa feed principally as "herbivores" of plant and insect exudates. Based on nitrogen (N) isotope ratios of plants, known herbivores, arthropod predators, and ants from Amazonia and Borneo, we find that many arboreal ant species obtain little N through predation and scavenging. Microsymbionts of ants and their hemipteran trophobionts might play key roles in the nutrition of taxa specializing on N-poor exudates. For plants, the combined costs of biotic defenses and herbivory by ants and tended Hemiptera are substantial, and forest losses to insect herbivores vastly exceed current estimates.

Feeding extensively on plant exudates and honeydews, many tropical arboreal ant species exhibit δ 15 N values characteristic of herbivores. Consistent with hypothesized herbivory, these taxa behave in feeding assays as though more N-deprived than are strictly carnivorous ants. However, to an as yet uncertain degree, relationships with N-upgrading and/or recycling microsymbionts may lower isotopic ratios, making ants appear to be more herbivorous than they actually are. Nutritional (N) contributions from microsymbionts have been inferred for a variety of ant taxa based on intracellular or extracellular associations between ants and bacteria. However, stronger and more specific inferences are possible when variability in microsymbiont locations within the digestive system is considered in the context of taxonomic variability in ant diets and digestive anatomy. Diets of exudate feeders may vary predictably in ratios of usable carbohydrates (CHOs) to N, depending on the extent to which they tend melezitose-producing Homoptera. Status of the peritrophic membrane, proventricular structure, and number and placement of Malpighian tubules can be interpreted as traits contributing to supply of N and/or CHOs to microsymbionts. In general, a more integrative understanding of ant diets, digestive anatomy, and associated microsymbionts helps to set out specific hypotheses to be tested experimentally and (where possible) in a phylogenetic context.

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Disparities in liquid-feeding performances of major ant taxa have likely been important to resource partitioning among ants, to the nature and composition of ant partnerships with plants and sap-feeding trophobionts, and to ecological and evolutionary diversification of ant taxa. We measured performance volumetrically for individual workers of 77 ant species from lowland rain forests of Amazonia and Borneo and three key North American taxa. In trials with 9% sucrose solution, performances were strongly related to body size (and alitrunk length) and to proventricular structure at generic to subfamilial levels. Highly modified proventriculi were associated with disproportionately large load sizes in Formicinae and certain small-bodied Dolichoderinae. These same taxa also ingested liquids more rapidly during foraging than did similar-sized species with plesiomorphic proventriculi. Secondarily reduced foraging performances of several formicines likely reflect ecological or evolutionary trade-offs related to dietary specialization or anti-predator defenses. Across formicines and dolichoderines, performances differed by functional group. Relatively small loads and slow uptake characterized species tending trophobionts (mainly Hemiptera) day and night in large worker aggregations. Large loads and rapid uptake typified solitary, diurnal "leaf-foragers." Intermediate feeding performances characterized a few species that both tended trophobionts in small aggregates and frequently foraged alone.

Honey bees, the primary managed insect pollinator, suffer considerable losses due to Deformed wing virus (DWV), an RNA virus vectored by the mite Varroa destructor . Mite vectoring has resulted in the emergence of virulent DWV variants. The basis for such changes in DWV is poorly understood. Most importantly, it remains unclear whether replication of DWV occurs in the mite. In this study, we exposed Varroa mites to DWV type A via feeding on artificially infected honey bees. A significant, 357-fold increase in DWV load was observed in these mites after 2 days. However, after 8 additional days of passage on honey bee pupae with low viral loads, the DWV load dropped by 29-fold. This decrease significantly reduced the mites’ ability to transmit DWV to honey bees. Notably, negative-strand DWV RNA, which could indicate viral replication, was detected only in mites collected from pupae with high DWV levels but not in the passaged mites. We also found that Varroa mites contain honey bee mRNAs, consistent with the acquisition of honey bee cells which would additionally contain DWV replication complexes with negative-strand DWV RNA. We propose that transmission of DWV type A by Varroa mites occurs in a non-propagative manner.

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In primary lowland rain forest in Brunei Darussalam, we studied arboreal ant communities to evaluate whether densities and spacing of spatially territorial taxa along 2.9 km of well‐studied trails are consistent with existence of a continuous mosaic of dominant ants. A median intercolony distance of 24.5 m, about twice or less distances over which colonies of most included species regularly ranged, suggested a relatively continuous mosaic. Despite relying on nesting sites in preformed plant cavities, carpenter ants contributed > 70 percent of mapped colonies. Most belonged to the Camponotus (Colobopsis) cylindricus (COCY) complex, including SE Asia's ‘exploding’ ants. Their lack of aggression against certain Polyrhachis species was associated with interspecific territory sharing by members of the two groups, and with a dominance‐discovery trade‐off. Experimental approaches yielded evidence for two putative contributors to positive association. Larger‐bodied Polyrhachis parasitize food‐finding abilities of smaller, more populous Camponotus workers, and the two taxa cooperate in territorial defense. Highly territorial and predatory weaver ants (Oecophylla smaragdina) were an important component of the ant mosaic in primary forest, second only to codominant COCY and Polyrhachis taxa. Members of the genus Crematogaster were significantly associated with Oecophylla in baiting censuses and regularly monopolized near‐nest baits to the exclusion of weaver ants. Litter ant abundances differed between territories of Oecophylla and less predatory COCY species, but direction of difference was inconsistent over time. The densely packed mosaic of spatially territorial, and differentially predatory, taxa in Bornean rain forest likely contributes to spatial variation in ant effects on plant and arthropod communities.

BackgroundThe small hive beetle (Aethina tumida; ATUMI) is an invasive parasite of bee colonies. ATUMI feeds on both fruits and bee nest products, facilitating its spread and increasing its impact on honey bees and other pollinators. We have sequenced and annotated the ATUMI genome, providing the first genomic resources for this species and for the Nitidulidae, a beetle family that is closely related to the extraordinarily species-rich clade of beetles known as the Phytophaga. ATUMI thus provides a contrasting view as a neighbor for one of the most successful known animal groups.ResultsWe present a robust genome assembly and a gene set possessing 97.5% of the core proteins known from the holometabolous insects. The ATUMI genome encodes fewer enzymes for plant digestion than the genomes of wood-feeding beetles but nonetheless shows signs of broad metabolic plasticity. Gustatory receptors are few in number compared to other beetles, especially receptors with known sensitivity (in other beetles) to bitter substances. In contrast, several gene families implicated in detoxification of insecticides and adaptation to diverse dietary resources show increased copy numbers. The presence and diversity of homologs involved in detoxification differ substantially from the bee hosts of ATUMI.ConclusionsOur results provide new insights into the genomic basis for local adaption and invasiveness in ATUMI and a blueprint for control strategies that target this pest without harming their honey bee hosts. A minimal set of gustatory receptors is consistent with the observation that, once a host colony is invaded, food resources are predictable. Unique detoxification pathways and pathway members can help identify which treatments might control this species even in the presence of honey bees, which are notoriously sensitive to pesticides.