Time and again, over hundreds of millions of years, environmental disturbances have caused mass extinctions of animals ranging from reptiles to corals. The anthropogenic loss of species diversity happening now is often discussed as the ‘sixth mass extinction' in light of the ‘Big Five' mass extinctions in the fossil record. But insects, whose taxonomic diversity now appears to be threatened by human activity, have a unique extinction history. Prehistoric losses of insect diversity at the levels of order and family appear to have been driven by competition among insect lineages, with biotic replacement ensuring minimal net losses in taxonomic diversity. The end-Permian extinction, the ‘mother of mass extinctions' in the seas, was more of a faunal turnover than a mass extinction for insects. Insects' current biotic crisis has been measured in terms of the loss of abundance and biomass (rather than the loss of species, genera, or families) and these are essentially impossible to measure in the fossil record. However, should the ongoing loss of insect abundance and biomass cause the demise of many insect families, the current extinction event may well be the first sudden loss of higher-level insect diversity in our planet's history. This is not insects’ sixth mass extinction—in fact, it may become their first.

Over the past 30 yr, multiple species of predatory Coccinellidae, prominently Coccinella septempunctata L. and Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) have spread to new continents, influencing biodiversity and biological control. Here we review the mechanisms underlying these ecological interactions, focusing on multi-year field studies of native and non-native coccinellids and those using molecular and quantitative ecological methods. Field data from Asia show that H. axyridis, C. septempunctata, and Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) are regularly among the most abundant predatory species but their rank varies by habitat. Studies of these species in their native Asian range, primarily related to their range in mainland China, document different patterns of seasonal abundance, species specific associations with prey, and habitat separation. Intraguild predation is well documented both in Asia and in newly invaded areas, and H. axyridis benefits most from this interaction. Harmonia axyridis also seems to rely more on cannibalism in times of prey scarcity than other species, and relatively sparse data indicate a lower predation pressure on it from natural enemies of coccinellids. Declines in the abundance of native coccinellids following the spread and increase of non-native species, documented in several multi-year studies on several continents, is a major concern for native biodiversity and the persistence of native coccinellid species. We suggest that future studies focus more attention on the community ecology of these invasive species in their native habitats.

The association between insect herbivores and vascular plants represents one of the greatest success stories in terrestrial evolution. Specific mechanisms generating diversity in the association remain poorly understood, but it has become increasingly clear that microbes play important roles in mediating plant–insect interactions. Previous research on phytoplasmas (Acholeplasmatales: Acholeplasmataceae), a diverse group of plant-pathogenic bacteria, and their hemipteran insect vectors suggests that this system provides a new model for understanding how interactions among distantly related but ecologically associated groups of organisms can drive evolutionary diversification. Phytoplasma infections affect the phenotypes of both plants and vectors, altering functional traits (e.g., diet breadth) and mediating host shifts which may, in turn, alter genetic and phylogenetic patterns. This review highlights previous research on the functional ecology and phylogenetic components of phytoplasma-plant-vector (PPV) associations relevant to the evolutionary diversification of this system. Although phytoplasmas and their hosts occur in most terrestrial biomes and have evolved together over the past 300+ million years, major gaps in knowledge of PPV associations remain because most prior research on the system focused on strategies for mitigating effects of phytoplasma diseases in agroecosystems. Study of this system within a broader evolutionary context could help elucidate mechanisms by which interactions between insect herbivores, microbes, and plants drive biological diversification and also help predict the emergence of diseases affecting agriculture. Future research should more thoroughly document PPV associations in natural habitats, examine the relative prevalence of cospeciation versus host shifts in this system, and test possible macroevolutionary consequences of host manipulation by phytoplasmas.

Cover crops (CC) support populations of pest and beneficial arthropods. The status of these arthropods in the subsequent cash crop depends on several factors such as CC species, management, biomass production, and weather conditions. A systematic review was performed to identify how CC management influences pest and beneficial arthropods and to identify knowledge gaps for the future research efforts. Eight studies included in this review indicated that CC increase beneficial arthropods or some beneficial arthropods compared with the CC managed fields. A minority of the studies indicated an increase in pest presence when using CC. Cover crop species, termination time and methods, and CC management had variable responses on arthropod activity-density. The variable responses, differences on study designs, and complexity of CC management influence arthropod activity in a CC-corn [Zea mays L. (Poaceae)]/soybean [Glycine max L. (Fabaceae)] system, limiting our ability to draw a broad and effective conclusion about the CC management impact on arthropods. Local research studies are needed to identify the impact of CC biomass quality and quantity, CC biomass thresholds for pest and beneficial arthropods, and cash crop yield impact of CC management-arthropod-related studies. Studies using the standard farming practices of each U.S. region and using standard measurements are needed to guide farmers that use cover crops. This systematic review aims to provide a better understanding of how the complexity of management in cover crop-corn/soybean management affects arthropod activity-density and to identify potential gaps in research and address future research needs.

To control non-native species, resource managers may import and introduce biocontrol agents. Like accidentally introduced insects, biocontrol agents must overcome several abiotic and biotic obstacles to establish successfully. They can also have varying efficacy and negative or positive impacts on native species and ecosystems. Given the similarities between accidentally introduced insects and biocontrol agents, researchers studying these organisms can more effectively communicate and actively link data to improve overall understanding and management of non-native species within the framework(s) of invasion theory. To assess interdisciplinarity between invasion ecologists and biocontrol practitioners that study insects in forests, we identified 102 invasion ecology and 90 biocontrol articles published from 2006 to 2018. These articles helped us determine which broad disciplines (invasion ecology, biocontrol, other control, other ecological, and nonecological) and publication formats (e.g., journals and books) the authors cited most. We found 1) invasion ecologists primarily cite other invasion ecology research; 2) biocontrol researchers cite biocontrol and invasion ecology research; 3) both disciplines primarily cited peer-reviewed journal articles; and 4) there was 65–70% overlap in the top 20 journals cited in primary invasion ecology and biocontrol literature. Though we found some cross-communication, it is currently mostly unidirectional, whereby invasion ecology informs biocontrol. We identify and discuss three areas—1) ecological principles governing success or failure of introduced species, 2) the invasion process, and 3) negative impacts on native species—for which the disciplines possess substantial overlap to demonstrate that biocontrol agents can provide invasion ecologists with an unconventional model to study the mechanisms of species invasion.

The well-diversified Latin American agriculture plays an essential role in the economy of that region, through the export of food and agricultural commodities. The region is expected to continue playing a significant role in world agricultural production and trade. Carabid beetles are efficient consumers of arthropod pests and weed seeds on agricultural land, which makes them a target for studies by entomologists aiming to determine whether predatory carabids are capable of suppressing pest populations. However, carabids have been mostly studied in temperate regions of the Northern Hemisphere. Here, evidence for carabids as biocontrol agents of agricultural pests in Latin America is examined, aiming to improve understanding of this predator group in Latin American agroecosystems. The records found were organized into the following subject areas: conservation tactics, biocontrol agents, agricultural practices, and population survey. The literature review identified several gaps in knowledge of these topics, which made it possible to indicate potential research projects related to noncrop habitats, population studies, and consumption of weed seeds. Laboratory investigations of carabids' predatory capacity indicated that they have the potential to control pests. However, field studies have failed to demonstrate that carabids significantly decreased pest densities. Although polyculture is a traditional practice of smallholder farmers in Latin America, the literature involving carabids and this sustainable agriculture practice is sparse. Looking forward, the utilization of polyculture and the existing no-till system in large fields provide opportunities for future research on ground beetles in Latin America.

Invasive plant introductions are increasing globally, and trends in human activity suggest these increases will continue. Although we know much about interactions between invasive herbaceous plants and arthropod communities, there is a dearth of knowledge examining interactions between invasive woody plants and arthropod communities. What information does exist shows that invasive woody plant relationships with mutualists (e.g., pollinators), herbivores, twig- and stem-borers, leaf-litter and soil-dwelling arthropods, and other arthropod groups are complex and hint at multiple factors influencing effects. These relationships warrant additional attention to allow better prioritization of species for research and regulatory review. Chinese tallow tree, e.g., is renowned for its attractiveness to honeybees, whereas reduced pollinator populations are found among other invasive woody plants such as privet. The unknown driving mechanisms and interactions that create these differences represent a substantial gap in knowledge and warrant additional research. Our objectives are to review current knowledge regarding invasive woody plants and their interactions with various arthropod groups in the United States, outline future research needs, and present a call to action regarding invasive woody plant research.

Wolbachia is one of the most common intracellular symbionts among insects, but the function of this infection and its effects on the host still remain largely unknown for many taxa. In the case of many social insects, living in colonies results in close interactions, facilitating the dispersion of the symbiont. However, having only one caste responsible for reproduction (queens) could restrict infections. Several groups of social insects have been reported to be highly infected with these symbionts. However, Wolbachia associations across social and closely related non-social insects in a comparative framework has not been examined to date, which may help us understand the role social behavior, geography, and ecology plays in structuring this association. Since 2006 the Multi-Locus Sequencing Type (MLST) approach has been shown to be appropriate for diversity studies, which consists of sequencing five genes spread across the Wolbachia genome. Over the past 15 yr, studies using this approach have been conducted worldwide and have generated large volumes of data. In this review article, we intend to produce a meta-analysis by combining MLST data from across social insects (ants, bees, termites, wasps) and beyond, together with their closest relatives to better elucidate the patterns behind the diversity of this symbiotic interaction. Our main findings reveal that the diversity of Wolbachia (supergroups) is correlated with the host insect taxonomy, biogeography, and social/solitary behavior. In addition, solitary insects such as bees and wasps can interact with a greater diversity of Wolbachia supergroup compared to their social representatives.

Cohesion in social insect colonies is maintained by use of chemical signals produced by the queen, workers, and brood. In honey bees in particular, signals from the queen and brood are crucial for the regulation of reproductive division of labor, ensuring that the only reproductive female individual in the colony is the queen, whereas the workers remain reproductively sterile. However, even given this strict level of control, workers can, in principle, activate their ovaries and lay eggs. Although much is known about the behavioral and physiological traits that accompany the switch from worker sterility to being reproductively active, much less is known regarding the molecular changes that accompany this switch. This review will explore what is known about the genes and molecular pathways involved in the making of laying workers/false queens in the Cape honey bee, Apis mellifera capensis Eschscholtz, through an analysis of the basis for thelytoky in this subspecies, the exocrine glandular chemistry of reproductively dominant workers and what is known about the biosynthesis of their pheromone components. This review will contribute to our understanding of the genetic regulation of thelytoky and the molecular mechanisms that govern reproductive division of labor in honey bees and provide generalizations that may be applicable to other social hymenoptera using this evolutionary fascinating example of worker reproduction.

Evidence synthesis and knowledge translation are scientific methodological approaches used across different disciplines for combining results from individual studies, interpreting them based on the body of evidence and with the objective of supporting decision-making. Systematic, rapid, and scoping reviews have a direct application in human health and social care, but also in veterinary medicine, which are areas that can overlap with medical and veterinary entomology. As a scientific field, the objective of medical and veterinary entomology is to identify and quantify the role of insects as transmitters of important arthropod-borne pathogens, thus contributing to the study of human and veterinary issues of public health importance. The main objectives of this review are to introduce to entomologists the most common knowledge translation and synthesis methods described in the literature, to then review the use of systematic, rapid, and scoping reviews applied in the medical and veterinary entomology field, using a systematized review approach. We found 120 relevant articles in the literature addressing topics related to medical and veterinary entomology and using systematic reviews of the literature or other evidence synthesis methods, which is concurrent with the ongoing trend towards the use of these methodologies. The application of unbiased approaches to entomology in general, and to medical and veterinary entomology in particular, will strengthen science- and evidence-based conclusions to be used as a tool for informing policy, decisions, and interventions.

The coconut rhinoceros beetle (CRB: Oryctes rhinoceros Linnaeus) is one of the most damaging pests to coconut and oil palms in Asia and the Pacific Islands. Adults bore into the crown and damage developing fronds, which affects tree development and yield. The insect is native to South and Southeast Asia and was inadvertently introduced into the Pacific in 1909. It has since spread to several Pacific island nations and territories, causing significant economic impact on these important coconut and palm-growing regions. In the 1950s and 1960s, an international biological control effort was initiated to search for and release natural enemy species. Release of the Oryctes rhinoceros nudivirus Huger (OrNV) and the species complex of Metarhizium Sorokin (Hypocreales: Clavicipitaceae) was successful in controlling CRB in its invaded range. Recently a new biotype of the beetle, known as CRB-G, has spread into the Pacific Islands causing unprecedented levels of damage due to the failure of previously successful biological control agents (BCAs) to suppress this biotype. The re-emergence of CRB as a serious pest warrants a rigorous re-evaluation of potential BCAs and a new search for effective natural enemies if necessary. In this article, we review literature on CRB to 1) analyze past introductions of BCAs and their effectiveness; 2) identify potentially important natural enemies and their geographical origins; and 3) assess possible approaches for utilization of BCAs against the new wave of CRB invasion. Research gaps and directions deserving future attention are highlighted and a strategy for renovation of biological controls for CRB suggested.

The diversity and abundance of native bees (Hymenoptera: Anthophila) are important in providing pollination services to a diverse array of crops. An extensive literature base is available on the contributions of bees as crop pollinators. The focus of the majority of these studies are on honey bees (Apis spp.) pollinating crops that depend on cross-pollination to produce a yield. Self-pollinating crop species, including cotton, soybeans, coffee, and canola, can self-pollinate but there is increasing evidence that they can also benefit from cross-pollination by insects. These crops can see a considerable benefit when visited by bees in general, but contradictory evidence is not fully understood in some systems. For example, recent studies have shown that bee visitation to cotton blooms can increase yield up to 15%. Including nesting habitat for non-Apis bees within soybean dominated landscapes increases in-field yields. However, in these same systems, some studies show none or minimal yield increases. Additional literature (both recent and historical) of non-Apis bees in mass-flowering self-pollinating crops and their potential benefits to the crops also exists but is previously unsynthesized in cotton and soybeans in particular. In our review of literature on these select self-pollinating crops, there appears to be apparent gaps in the literature base on these and other understudied cropping systems. With the exception of graminaceous and cereal crops, all the crops discussed herein seem to have all have benefited from visitation by both Apis and non-Apis bees. Some provide known resource benefits to native bee pollinators like canola, but others like cotton and soybean are not well understood. Further, with an apparent yet small literature base in cotton and soybean there are many facets between the native bee pollinators and crop such as nutritional benefits of nectar and pollen to the bees themselves that still need to be addressed. To examine these underlying mechanisms, additional studies into the basic biology and natural history, including nesting habitats and preferences along with foraging preferences of abundant bee species will help understand how these bees seem to persist and possibly thrive in intensified agricultural systems.

Global biodiversity declines are attributed to many factors, including landscape fragmentation and vegetation homogenization. These patterns may be exacerbated by the intensification of management in agroecosystems, as management to meet the increasing demand for food, fuel, and fiber often comes at the cost of biodiversity and subsequent ecosystem functions and services. Conserving biodiversity will be necessary to create sustainable agroecosystems capable of optimizing both production and services such as pollination. We conducted a meta-analysis with 109 studies to examine the relationship between plant species richness and pollinator species richness to determine whether higher plant species richness supports higher pollinator species richness, especially in areas prone to biodiversity losses. We found most groups of insect pollinators, including bees, butterflies, flies, moths, and wasps, responded positively to increasing plant species richness, irrespective of location or land use, suggesting the capacity to increase pollinator richness through management strategies that increase plant species richness. However, we found pollinators in manipulated studies did not consistently respond to increasing plant species richness despite the overall positive relationships in observational and experimental studies, highlighting the importance of plant selection when making management decisions aiming to improve pollinator richness. Additional studies in regions such as Africa and South America will help fill in latitudinal gradients and provide greater coverage necessary to refine patterns. Increasing plant species richness through management changes or restorations will likely increase pollinator richness and be beneficial in agroecosystems to support biodiversity.

Agricultural production is increasingly viewed as more than a source of food, feed, fiber and fuel, but also as a system of interdependent biotic and abiotic components that interact to produce ecosystem services and disservices. Weeds and insects are commonly viewed as non-desirable components of agroecosystems that should be managed. However, weeds can also provide benefits to cropping systems, such as providing resources and habitat to pollinators and other beneficial arthropods. This review on weed–insect interactions in annual cropping systems focuses on functional interactions within the context of regulating and supporting ecosystem services and disservices. Regulating services are those that act as regulators of the environment, such as weed–insect interactions that contribute to the regulating services of pollination and biological control, but also contribute to the disservices of crop and cover crop seed predation, and maintenance of insect pests and insect-transmitted phytopathogens. Supporting services include habitat and biodiversity that are necessary for the production and maintenance of the other types of ecosystem services. Here we review the impacts of weed–insect interactions as a component of biodiversity.We conclude by identifying some knowledge gaps that hinder our understanding of trade-offs when seeking to improve net positive ecosystem services in annual cropping systems.

Graphical Abstract

Positive and negative interactions among insects and weeds. Credit: Nick Sloff.