Curculio elephas

Chestnut weevil
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Family:	Curculionidae
Subfamily:	Curculioninae
Genus:	Curculio
Species:	C. elephas
Binomial name
Curculio elephas (Gyllenhal 1836)

Curculio elephas is a species of beetle in the family Curculionidae, the true weevils. It is known commonly as the chestnut weevil. It is a serious pest of chestnut (Castanea sativa) in Europe.^[1]

Curculio elephas are similar to Curculio sayi and in the United States. 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. ^[2] The adult female weevil drills a hole in a chestnut fruit and deposits one egg inside. The eggs are laid into the cupules or around the peduncle joints. Eggs hatch in five to seven days producing large, legless grubs. When the larva 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. Larvae may pupate in the soil for one season or for several years. The following July, they turn into pupae. The adult emerges and lives in the canopy of the chestnut tree.^[1]

Infestation[]

Curculio elephas

The adult weevils can be scouted and monitored for their presence by jarring the tree and counting fallen weevils. ^[2] In some chestnut-growing regions, infestation of the fruit by weevil larvae can reach 90%.^[1] Annually, about 20–30% of harvested chestnuts in China are wasted and spoiled by insect infestation and mildew. ^[3] In Hungary, Curculio elephas swarms in chestnut orchards around August 20, particularly strongly around noon and in sunny weather.
The larvae of the chestnut weevil can only chew their way out of a fallen nut, so breeding 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.

Curculio elephas is not limited to the chestnut. It is also a main predator of the seeds of holm oak (Quercus ilex). The larvae feed and develop inside the acorns.^[4] Planting chestnut orchards beside turkey oak forests is not advised in Europe, because both trees are susceptible to the chestnut weevil (which also uses the turkey oak acorn to develop), and the turkey oak trees can pass it on to the chestnut trees.^[5]

Controls[]

Timing the harvests to pick up the chestnuts as soon as they fall reduces the numbers of the overwintering 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. ^[2] Other suggested control methods include the use of biological pest control agents, such as fungi and physical controls such as radio waves and heat.^{[6] [7]}

A warm, aerosol-based protection has been developed for older trees, by Sifter and Bürgés in 1971.

Most insects in postharvested fruits and nuts can be controlled by thermal treatments over a temperature range of 46-56 °C. ^{[8] [9] [10] [11]} Weevil damage can be reduced by gathering nuts daily, and heating them to 120ºF (49C) for 20 to 30 minutes to kill larvae in the nuts. ^[2]

References[]

Media related to Curculio elephas at Wikimedia Commons