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Diabrotica

Genus of beetles

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There are an estimated 400 species grouped into the genus Diabrotica. Within Diabrotica there are 3 series: fucata, virgifera, and signifera groups. The fucata series contains the majority of Diabrotica diversity with 354 species. Fucata are characterized as multivoltine, producing two broods of offspring per year. The virgifera series comprises 24 species, and the signifera series contains 11. Additionally, virgifera and signifera are characterized as univoltine, and will only brood one set of offspring annually.

There is very limited information on most species of Diabrotica. Majority of the research conducted on the Diabrotica genus focuses on investigating species of consequential economic importance, such as D. balteata, D. barberi, D. undecimpunctata howardi, D. virgifera, D. speciosa. Multiple Diabrotica species are considered major agricultural pests, therefore the control and management of populations is of significant importance to farm management strategies.

Taxonomy and evolutionary history

The Diabrotica genus arose in the Cretaceous period and began to diversify and speciate ~60 million years ago, which culminated ~30-40 million years ago. Contrary to previous suggestions, Diabrotica speciation was not linked to the onset of corn and other crop cultivation. Gene sequencing has led to a phylogenetic reconstruction of the Diabrotica genus that indicates monophagy is the ancestral trait. The genus began to diversify when certain lineages expanded their diets to include a multitude of different types of plants, leading to a polyphagous trait. However, subsequent reversals back to monophagy or oligophagy have occurred in some evolutionary branches.

The diversification and evolution of Diabrotica species is closely linked to their relationship with wild plant species in the family Cucurbitaceae (cucurbits), which characteristically produce cucurbitacin secondary compounds. Cucurbitacins are bitter and toxic. While cucurbitacins deter most herbivores, Diabrotica beetles are attracted to cucurbitacins and compulsively feed on cucurbit species, especially the tissues that contain high concentrations of cucurbitacins, such as roots, seeds, and cotyledons. Diabrotica beetles favour cucurbitacin-containing plants to the extent that they will leave another nutritious plant host for a cucurbit plant. The mouthparts of Diabrotica beetles display receptors that bind cucurbitacins to stimulate this compulsive feeding behaviour. By feeding on cucurbit plants and sequestering cucurbitacin in their haemolymph, Diabrotica beetles are afforded some protective advantages, such as chemical defenses against natural predators. This is an example of pharmacophagy, in which insects consume plant metabolites for reasons besides nutrition. The aforementioned demonstrates a situation of chemically mediated coevolution between Diabrotica and cucurbit plants, and even Diabrotica species that have evolved to no longer rely on cucurbitacin-containing plants still demonstrate this compulsive feeding behavior in the presence of these plants.

Diabrotica species are separated into 3 groups: virgifera, fucata, and signifera. These are ‘groups of convenience’ as they are based on host range, diet, life history, and other ecological traits, rather than being supported by molecular and genetic data.

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Monotypic taxonTaxonomic group with only one subordinate taxonSpecies descriptionFormal description of a discovered speciesParaphylyType of taxonomic groupIUCN Red ListInventory of the global conservation status of biological speciesSubtropicsGeographic and climate zoneCommon nameName generally used for a taxon, group of taxa or organism(s)