''Curculio elephas'' is a species of

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

in the family

Curculionidae The Curculionidae are a family of weevils, commonly called snout beetles or true weevils. They are one of the largest animal families, with 6,800 genera and 83,000 species described worldwide. They are the sister group to the family Brentidae. T ...

, the true

weevil Weevils are beetles belonging to the Taxonomic rank, superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and Herbivore, herbivorous. Approximately 97,000 species of weevils are known. They b ...

s. It is known commonly as the chestnut weevil. It is a serious pest of

chestnut The chestnuts are the deciduous trees and shrubs in the genus ''Castanea'', in the beech family Fagaceae. They are native to temperate regions of the Northern Hemisphere. The name also refers to the edible nuts they produce. The unrelat ...

(''Castanea sativa'') in Europe.Paparatti, B. & Speranza, S. (1999)
Biological control of chestnut weevil (''Curculio elephas'' Gyll.; Coleoptera, Curculionidae) with the entomopathogens fungus ''Beauveria bassiana'' (Balsamo) Vuill.(Deuteromycotina, Hyphomycetes).
''In'': II International Symposium on Chestnut 1998. pp. 459-466. ''Curculio elephas'' are similar to '' Curculio sayi'' and '' Curculio caryatrypes'' in the United States.

Development

Adults feed on chestnut foliage until nut kernels enter the dough stage in mid to late August. Although they can lay eggs any time after kernel filling, most eggs are laid after the bur begins to open. The adult female weevil drills a hole in a chestnut fruit and deposits one egg inside. The eggs are laid into the

cupule A cupule is a small structure shaped like a cup, including: * In archeology, rock cupules are circular man-made hollows on the surface of a large rock or a rock slab ** On a smaller artifact they are called a cupstone. * In botany: the base of an ...

s or around the peduncle joints. Eggs hatch in five to seven days producing large, legless grubs. When the

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

emerges from the egg it feeds on the developing chestnut. The larvae leave behind frass and excrement. Infested nuts may contain several weevil larvae or weevil burrows filled with excreta. Upon chestnuts fall, the larvae chew their way out of the nuts and retreat into the ground. They immediately bury themselves several centimeters deep in the soil. The following July, the larvae turn into

pupa A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...

e. Pupae may be in the soil for one season or for several years due to prolonged larval diapause in some individuals. Adult weevils from an extended diapause, emerge, on the average, 1–10 days before those with a simple diapause. The emergence of adult weevils occur always from mid-August to early October. The emerged adults live in the canopy of the chestnut tree. When a summer is dry, some adults cannot emerge because of the hardness of the soil. Emergence success of females can be between 27–78% versus males. The result is that the sex ratio is female-biased before soil emergence and male-biased after. The year after a summer drought, many reproducing females may emerge from larvae with prolonged diapause.

Infestation

''Curculio elephas'' is not limited to the chestnut. It is also a main predator of the acorns of

holm oak Holm oak may refer to: * '' Quercus ilex'', tree native to South and Southeast Europe and parts of France * '' Quercus rotundifolia'', tree native to the Iberian Peninsula and Northwest Africa * ''Quercus agrifolia ''Quercus agrifolia'', the Cal ...

(''Quercus ilex'') and

turkey oak Turkey oak is a common name for several species of oaks and may refer to: *''Quercus cerris'', native to southeastern Europe and Asia Minor *''Quercus laevis ''Quercus laevis'', the turkey oak, is a member of the red oak group of oaks. It is nat ...

. The larvae feed and develop inside the

acorn The acorn, or oaknut, is the nut of the oaks and their close relatives (genera ''Quercus'' and '' Lithocarpus'', in the family Fagaceae). It usually contains one seed (occasionally two seeds), enclosed in a tough, leathery shell, and borne ...

s. Planting chestnut orchards beside turkey oak or holm oak stands is not advised in Europe, because both trees are susceptible to the chestnut weevil. Infested holm oak and turkey oak acorns can pass weevils on to chestnut trees.''The pest control of the Chestnut tree''
by Dr Péter Szentiványi. Chestnut – Agricultural Publisher. For Sarkpont Cc., Hungary. The adult weevils can be scouted and monitored for their presence by jarring the tree and counting fallen weevils on a white surface. The larvae of the chestnut weevil must chew their way out of a fallen nut. Increased orchard infestation occurs mostly where chestnuts lie on the ground for a sufficient length of time, or where the trees produce many small fruits which remain behind at the harvest. This allows many larvae to develop and burrow into the ground of an orchard. In some chestnut-growing regions, infestation of the fruit by weevil larvae can reach 90%. In China, in 2001, annually, about 20–30% of harvested chestnuts were wasted and spoiled by insect infestation and mildew. In Hungary, ''Curculio elephas'' swarms in chestnut

orchard An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit- or nut-producing trees which are generally grown for commercial production. Orchards are also sometimes a feature of larg ...

s around August 20, particularly strongly around noon and in sunny weather.

Controls

Timing the harvests to pick up the chestnuts as soon as they fall reduces the numbers of the

overwinter Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...

ing larvae. Regular soil work is also unfavourable to its life habits. Chemical control of the pest is difficult or unsustainable. Sevin is the only insecticide registered in the US for chestnuts. Applications have proven effective if applied during the mating and early egg-laying period, from early August to mid-September. Other suggested control methods include the use of

biological pest control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

agents, such as fungi and physical controls such as radio waves and heat. In Turkey, soil treatments underneath a gomu with

entomopathogenic Entomopathogens are pathogens that infect insects. Entomopathogens include: * Entomopathogenic fungus * Entomopathogenic nematode * Entomopathogenic virus * Entomopathogenic bacterium See also * Arbovirus * List of insect-borne diseases Thi ...

Metarhizium brunneum ''Metarhizium brunneum'', is the re-instated name of a group of reassigned ''Metarhizium'' isolates, previously grouped in the species "''Metarhizium anisopliae'' var. ''anisopliae''": based on a multigene phylogenetic approach using near-comple ...

strains ARSEF 4556 and V275 alone and in combination with the entomopathogenic nematodes

Heterorhabditis bacteriophora ''Heterorhabditis bacteriophora'' is a species of entomopathogenic nematode known commonly as beneficial nematodes. They are microscopic and are used in gardening as a form of biological pest control. They are used to control ants, fleas, moths, ...

have been successful. In Hungary, in 1971, a warm, aerosol-based protection was developed for older trees, by Sifter and Bürgés. Weevil damage can be reduced by gathering nuts daily to reduce development time before thermal treatment. Most insects in postharvested fruits and nuts can be controlled by thermal treatments over a temperature range of 46-56 °C. Mycoflora and market quality of chestnuts treated with hot water to control the chestnut weevil, JM Wells, JA Payne - Plant Disease, 1980 - apsnet.org Heating gathered chestnuts to 120ºF (49C) for 20 to 30 minutes kills developing eggs and larvae in the nuts. Bruce Bordelon, Department of Horticulture and Landscape Architecture,

Purdue University Purdue University is a public land-grant research university in West Lafayette, Indiana, and the flagship campus of the Purdue University system. The university was founded in 1869 after Lafayette businessman John Purdue donated land and money ...

, Chestnut Weevil

, 2016

References

Curculioninae Agricultural pest insects Beetles described in 1836 {{Curculioninae-stub