Diabrotica speciosa

D. speciosa can move locally by adult flight, and by movement of eggs, larvae or pupae in soil contaminating vehicles or farm machinery. For long-distance spread, adults could be present on host plants for planting, but these are not of the kind normally moved in international trade, and the active adults will not necessarily remain on their hosts. Larvae could be associated with ground crops like groundnuts or potatoes, and the underground parts of maize, wheat or soybean because they are unlikely to be moved. It also is not likely that the larval hosts would be traded as plants with soil.[4]

In their native and newly acquired habitats, D. speciosa is an important pest throughout southern South America (except Chile), but, being highly polyphagous (feeds on various foods), qualitative reports of its impact on different crops vary in different regions. It is considered an important pest of maize, cucurbits, and orchard crops throughout its distribution.[7] Although it migrates as an adult, no information on observed distances has been found.[5]

There is evidence that D. speciosa is a viral vector for comoviruses, southern bean mosaic virus, mimosa mosaic virus, tymoviruses (such as passionfruit yellow mosaic virus), carmoviruses, and purple granadilla mosaic virus.  D. speciosa transmitted cowpea severe mosaic virus (CPSMV – comovirus) to bean. Eggplant mosaic virus (EMV – tymovirus) was transmitted to tobacco by D. speciosa may also transmit bacterial wilt, caused by Erwinia tracheiphila, in cucurbits.[8]

Predators of D. speciosa are infrequent in their new habitats. This likely aids in their establishment.[7] D. speciosa is cold-tolerant and overwinters as an adult. This positively impacts their success in colder climates. They hide in the crown or rosettes of winter-growing plants. In the spring, adults emerge to feed on the host plant. Adults like to feed on pollen-rich flowers such as cucurbits, thistle, and sunflower. Eggs are oviposited on the soil close to a host plant. Larvae complete three instars while feeding on the roots of the host plant and pupate in the soil. Multiple generations are possible. In tropical areas, the cucurbit beetle reproduces continuously.[9]

Plant protection products are widely used to control D. speciosa, either applied to the soil to control larvae or to the above-ground parts to control adults (according to the crop concerned). Intensive use of products is required to control larvae in soil. In southern Brazil, IPM programs combine no-till agriculture, rotation of soybeans with maize or wheat, and use of insecticides only when damage is evident. Using this system, wheat is produced with virtually no pesticides in this area. Adults can be lured to baits composed of insecticide on the cucurbitacin-rich roots of wild cucurbits. Although some natural enemies of D. speciosa are known there is no prospect of biological control of this species.[4]

D. speciosa was added in 2002 to the European Plant Protection Organization (EPPO) A1 action list of pests, and endangered EPPO member countries are thus recommended to regulate it as a quarantine pest. In general, most EPPO countries prohibit the import of soil, and restrict the import of plants with soil,[2] from other continents. This measure should be effective against D. speciosa. Host plants should be free from the pest.[4]

The larvae of D. speciosa feed on roots of maize, wheat, groundnut, soybean and potato, and various other crop and non-crop hosts. The adults are highly polyphagous, being recorded on over 60 species, mainly vegetables, but are particularly associated with Cucurbitaceae (e.g., Cucurbita maxima, Cucurbita pepo).[10] They feed on every part of the plant above ground. In maize, their feeding on newly emerging silks prior to pollination is most serious, resulting in sparsely filled ears. Serial reduction in the number of ripening kernels from the tip of the ear to the base can often be observed at harvest. Whilst the adults do feed on young maize leaves, this is of secondary importance.[10]

D. speciosa threaten the lives of many crops and they act as vectors for many viruses, which contributes to human/animal health if consuming infected crops. They not only feasts on cucurbits but on beans, grapes, and potatoes too.[10] The damage caused reduces the amount of food available to the plant for growth, consequently lowering the yield. They can transmit plant diseases. The most commonly-spread are bacterial wilt and the cucumber mosaic virus. D. speciosa (Germar) is one of the chrysomelid more widely distributed in crops of Argentina. They can move locally by adult flight, and probably by movement of eggs, larvae or pupae in soil contaminating vehicles or farm machinery.[10] For long-distance spread, adults could be present on host plants for planting, but these are not of the kind normally moved in international trade, and the active adults will not necessarily remain on their hosts. Larvae could be associated with groundnuts or potatoes, but the underground parts of maize, wheat or soybean are unlikely to be moved. Nor is it likely that the larval hosts would be traded as plants with soil. Accordingly, the main potential pathway is soil as such.[10]