Ecology and Evolutionary History of Diabrotica Beetles—Overview and Update

Abstract

An overview is given on several aspects of evolutionary history, ecology, host plant use, and pharmacophagy of Diabrotica spp. with a focus on the evolution of host plant breadth and effects of plant compounds on natural enemies used for biocontrol of pest species in the group. Recent studies on each aspect are discussed, latest publications on taxonomic grouping of Diabrotica spp., and new findings on variations in the susceptibility of corn varieties to root feeding beetle larvae are presented. The further need for in-depth research on biology and ecology of the large number of non-pest species in the genus is pointed out.

Spotted cucumber beetle (Diabrotica undecimpunctata howardi) is attracted to vittatalactone, the pheromone of striped cucumber beetle (Acalymma vittatum)

“…Genetic analyses estimate that the genera Acalymma and Diabrotica diverged 45 (± 8, 95%CI) million years ago, and that the polyphagous fucata group of Diabrotica, of which D. u. howardi is a member, diverged from the oligophagous virgifera group 17 (± 4) Mya (Eben and Espinosa de los Monteros 2013). Although a D. u. howardi male-produced pheromone has not been identified, the continued affinity of D. u. howardi and other polyphagous Diabrotica species for cucurbitacin consumption and sequestration (Eben 2022) parallels with our findings of kairomonal attraction to the pheromone of the cucurbit specialist Acalymma. The eavesdropping kairomonal cross-attraction provides, through the related specialist beetles, a mechanism "tethering" the polyphagous beetles to their ancestral plant hosts.…”

“…The eavesdropping kairomonal cross-attraction provides, through the related specialist beetles, a mechanism "tethering" the polyphagous beetles to their ancestral plant hosts. Such eavesdropping is likely favored by natural selection given the value of cucurbitacins as defensive compounds against fungi, nematodes, and various other natural enemies to all life stages (e.g., Ferguson and Metcalf 1985;Tallamy et al 1998;Eben 2022).…”

“…We note that we have not yet determined the vittatalactone loading necessary to ensure that baits are more attractive than A. vittatum aggregations in the field, and this is worthy of future study. In addition, diversity and host affiliations among the many Diabrotica species are still not well-defined (Derunkov et al 2015;Eben 2022), and it remains to be determined whether there are other species with attraction to vittatalactone or other semiochemicals of Acalymma species. However, the discovery that two species of Anasa (squash bugs; Hemiptera: Coreidae) are also attracted to vittatalactone (Brzozowski et al 2022;Weber et al 2022), shows that cross-attraction to vittatalactone is not limited to the Chrysomelidae or even Coleoptera.…”

Undercover operation: Belowground insect herbivory modifies systemic plant defense and repels aboveground foraging insect herbivores

“…Cucumber beetles, in the genera Diabrotica and Acalymma, are important cucurbit herbivores, as larvae feed belowground on roots and adults feed aboveground on leaves, pollen, flowers, and fruits (Shapiro and Mauck, 2018). Cucumber beetles range from generalists that attack a wide variety of host plants, such as banded cucumber beetles (Diabrotica balteata LeConte), to specialists like the striped cucumber beetle (Acalymma vittatum F.) that exclusively feeds on cucurbits (Eben, 2022). For most cultivated cucurbits, crop breeding over evolutionary time resulted in an inability to produce defensive secondary metabolites called "cucurbitacins" (Theis et al, 2014;Brzozowski et al, 2019Brzozowski et al, , 2020b, raising intriguing questions about how cucurbitacin loss alters interactions with herbivores.…”

Host search behaviors of specialist and generalist root feeding herbivores (Diabrotica spp.) on host and non-host plants

“…Four Diabrotica species and subspecies including western corn rootworm (WCR), D. virgifera virgifera LeConte, northern corn rootworm (NCR), D. barberi Smith & Lawrence, southern corn rootworm (SCR), D. undecimpunctata howardi Barber, and Mexican corn rootworm (MCR), D. virgifera zeae Krysan & Smith, are economically important insect pests of corn ( Zea mays L.) in the United States 1 , 2 , costing over $2 billion annually in economic losses due to management costs and yield reductions 3 . These insect species are native to North America 1 and are commonly referred to as corn rootworms since their larvae primarily feed on the roots of corn 4 resulting in most of the damage caused by these pests (e.g., detrimental effects on nutrient and water uptake of corn plants, facilitation of pathogen infection, and reduced plant stability) 5 , 6 . Several management strategies (e.g., crop rotation, chemical insecticides, transgenic corn) have been developed to manage WCR and NCR; however, both these species have evolved adaptation to nearly all management tactics 7 – 12 .…”