Globally, 4 species of hazelnut-feeding weevils are recognized to exist: Curculio dieckmanni (A), Curculio nucum (B), Curculio obtusus (C), and Curculio occidentis (D). (Determine by Hailey Shanovich, initially printed in Shanovich and Aukema 2022, Journal of Built-in Pest Administration)
By Hailey Shanovich
Hailey Shanovich
Individuals across the globe are nuts about hazelnuts: In line with the Meals and Agriculture Group of the United Nations, the worldwide demand for hazelnuts is robust and rising. A lot in order that international locations akin to China and the US have been creating their very own hybrid hazelnut vegetation to extend yields and land space in manufacturing to get forward of the demand. Hazelnuts are more and more utilized in baked items and snack meals, and simply up to now few years Nutella has seen important will increase in gross sales.
Among the many most damaging insect pests of hazelnuts worldwide are weevils within the genus Curculio. Grownup feminine weevils lay eggs into creating hazelnuts, after which the newly hatched larvae feed on the kernel, the a part of the nut that people eat, till they attain maturity. They destroy the kernel, instantly impacting the yield of the crop. (See images.)
Grownup feminine Curculio weevils drill holes into creating hazelnuts to put eggs into them (left). Upon hatching, the larvae feed on the creating kernel till they attain maturity (proper). Grownup and larva proven listed here are each hazelnut weevil (Curculio obtusus). (Pictures by Hailey Shanovich)
In a new information printed in Could within the open-access Journal of Built-in Pest Administration, my colleague Brian Aukema, Ph.D., and I define the weevil species’ pure histories, and we offer an summary of what to anticipate over the approaching many years as hazelnut manufacturing expands. The prevailing literature on these species is essentially dated and in different languages, so a compilation of those works and a abstract of administration ways are indispensable for the rising business.
Biology
Worldwide, 4 species of hazelnut-feeding weevils are recognized, all inside the Curculio genus: C. dieckmanni in northeast Asia, C. nucum all through Europe, the hazelnut weevil (C. obtusus) in japanese North America, and the filbert weevil (C. occidentis) in western North America. All species injure hazelnuts in the identical method, they usually all have very related look as each larvae and adults, excluding C. dieckmanni adults, which differ in coloration. Curculio dieckmanni and C. nucum already are liable for devastating yield losses in untreated hazelnut orchards in China and Europe, respectively, whereas the hazelnut weevil stays essentially the most understudied, since industrial hazelnut manufacturing was not attainable in its geographic vary till the event of cold-hardy and disease-resistant hybrid vegetation.
Worldwide, 4 species of hazelnut-feeding weevils are recognized, all inside the Curculio genus, with distinct geographic ranges: C. dieckmanni (crimson), C. nucum (yellow), C. obtusus (inexperienced), and C. occidentis (blue). (Picture by Hailey Shanovich)
Administration
Administration of those weevils is mostly approached in a different way relying on the weevil species, area of hazelnut manufacturing, and even nation. Management strategies have been researched essentially the most in Europe and west Asia, as a result of nearly all of industrial hazelnut manufacturing has traditionally occurred there. Nonetheless, China has been making a lot headway in creating cultural and organic management methods for C. dieckmanni. The U.S. has carried out the least analysis and growth of management strategies for its weevil species, as hazelnut manufacturing has traditionally solely occurred within the Willamette Valley of Oregon, and C. occidentis, which happens there, usually prefers endemic oak species and barely causes financial injury to the crop.
Pesticides. The very best yield reductions in China and far of Europe are noticed when hazelnuts should not handled with pesticides. Nonetheless, many hazelnut growers all through Europe and Asia don’t use chemical substances for the management of insect pests, whereas some have resorted to 1 spray yearly to knock down the weevils throughout grownup emergence. In Turkey, the place nearly all of the world’s hazelnut manufacturing at present takes place, some natural pesticides choices have been explored and present promise for management of C. nucum.
Organic management. Naturally occurring insect-pathogenic fungi have been discovered to be extremely efficient, and insect-eating nematodes have been discovered to be efficient in controlling C. dieckmanni and C. nucum within the subject. Useful insect-eating nematodes have additionally confirmed profitable at killing C. nucum and C. occidentis within the subject. So far as insect pure enemies, they seem like far and few between for these weevils, because the larvae stay secure inside creating hazelnut shells or underground for many of their life cycle.
Cultural management. When it comes to cultural management methods, most within the toolbox are for C. dieckmanni in China. Newly developed hybrid hazelnuts, crosses from the European hazelnut (Corylus avellana) and the Asian hazelnut (Corylus mandshurica), are reportedly immune to C. dieckmanni. Cultivars of European hazelnut grown all through Europe are usually vulnerable to C. nucum, however a number of resistant ones have been recognized. Moreover, the enticing plant volatiles and the intercourse pheromone of C. dieckmanni have been recognized, which has led to the manufacturing of lures and traps for mating distribution of the species. In Turkey, bodily removing of grownup weevils, whether or not by hand or by shaking vegetation, is reportedly the preferred management methodology.
Outlook
The importance of hazelnut-feeding weevils will proceed to extend as manufacturing will increase globally. Importation of hazelnuts or motion of hazel vegetation between international locations may unfold these Curculio species to new areas, though the invasive potential of those species has but to be investigated. Additionally it is unknown if different Curculio species not talked about right here may emerge as pests of hazelnuts extra time as manufacturing is elevated. Future analysis is required on the biology, ecology, and administration of those weevils, particularly C. dieckmanni and the hazelnut weevil, that are every anticipated to pose financial considerations to China and the US’ rising hybrid hazelnut industries, respectively.
Hailey Shanovich is a Ph.D. candidate and analysis assistant on the College of Minnesota and present chair of the ESA North Central Department’s Pupil Affairs Committee. E-mail: shano004@umn.edu.
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