Snout Beetles & Where to Find Them

Curculionidae contains greater than 60,000 species, and as such it is the largest of all insect families (Whitfield & Purcell, 2012). It is a highly diverse group of beetles whose members may be found throughout the world. Approximately 1000 documented representatives of this family can be found in North America (data.nal.usda.gov, 2017). Some distinctive characters of this group are an elongated snout and geniculate antennae protruding from it (CPHST, 2011). However, pigmentation and body morphology vary greatly. Weevils can be smaller than a grain of rice or the length of a human finger. Some individuals are dull colors of gray, black, and brown while others sport spots, stripes, and iridescent elytra. In fact, bark beetles, miniscule pill-shaped wood-boring insects, are also included in this family, despite their apparent lack of a snout.

Weevil in the genus Odontocorynus on a flower at Midewin National Tallgrass Prairie.

Curculionids may be found in a broad range of habitats, as these successful creatures have adapted to highly specific ecological niches. (Whitfield & Purcell, 2012). While most are terrestrial, some aquatic and marine species have been identified (Whitfield & Purcell, 2012). Weevils and bark beetles are found in sand dune, forest, prairie, and savannah habitats in the Midwest and across the globe; there are few places where these resourceful and intriguing insects cannot be found.

Generally phytophagous, many weevils are well known agricultural pests, and cause damage to both trees and forbs. An example of one such species is Dendroctonus ponderosae, a bark beetle found in the Western United States which attacks pine forests. An individual of this species, once it has found a suitable tree to feed upon, releases pheromones which draw numerous others to the location. This behavior is lethal to the tree due to consumption of its phloem by the beetles. Another example is the accidentally introduced Canada Thistle Bud Weevil, which feeds on the reproductive structures of an invasive plant, the Canada Thistle. Unfortunately, this Curculionid is not a specialist, and also damages closely related native plants (Graham & Johnson, 2007). Cotton, alfalfa, row crops, and orchards are all similarly plagued by species within Curculionidae. Weevils impact food production, economics, and health of natural areas in ways of which most people are unaware.

A Canada Thistle Bud Weevil (Larinus planus) in Bourbonnais, IL.

Curculionids also provide ecosystem services as pollinators and biological control agents. While Hymenopterans and Lepidopterans are more effective, Coleopterans like weevils also contribute to plant reproduction through transferal of pollen. As mentioned before, the evolutionary success of this group is tied to their ability to adapt and specialize. In light of this, it should come as no surprise that some flowering plants have Curculionids as their primary pollinators. They are also occasionally helpful in management of invasive species, when mechanical and chemical control methods are ineffective or inappropriate. A long-term invasive aquatic plant in the United States and Canada is Eurasian Watermilfoil (Myriophyllum spicatum). This plant thrives in bodies of freshwater and has become so pervasive due to its ability to re-establish from broken portions given suitable sediment and growing conditions.

Invasive M. spicatum in Dewart Lake (Indiana) where weevils have recently been introduced.

In recent years tens of thousands of Euhrychiopsis lecontei have been introduced to lakes and ponds in multiple states in an effort to combat it, but the effectiveness of this method is currently a topic of research (Frew, 2017). Hopefully these introductions benefit damaged systems with few future repercussions. The delicate balance of ecological systems is easily tilted, and Curculionids seem to be on both sides. Some species have caused issues, while others may be the means to restoring balance.

One thing is certain, these extraordinary beetles compose one of the most ubiquitous and diverse groups of organisms on Earth, and therefore are integral to proper functioning of the natural world.

Weevil in the genus Tychius in a wetland area at Midewin National Tallgrass Prairie.

So, where can snout beetles be found? The answer is: everywhere.

References

Center for Plant Health Science and Technology (CPHST). (2011). Curculionidae (including Scolytinae and Platypodinae). Retrieved from http://idtools.org/id/wbb/families/Wood_Boring_Beetle_Keys/Woodboring_Families/Media/Html/Fact_sheets/Cucurlionidae.html

Franz, N. M., Chamorro, M. L., Fleming, D., Setliff, G. P., O'Brien, C. W. (2017). Weevils of North America (WoNA). Ag Data Commons. Retrieved from https://data.nal.usda.gov/dataset/weevils-north-america-wona

Frew, C. (2017). EXPLORING THE POTENTIAL FOR CONTROL OF EURASIAN WATERMILFOIL BY THE MILFOIL WEEVIL IN CHRISTINA LAKE , BRITISH COLUMBIA Bachelor of Science , University of Lethbridge , 2003 A Thesis Submitted to the School of Graduate Studies of the University of Lethbri. University of Lethbridge.

Graham, J., & Johnson, W. S. (2007). Managing Canada Thistle: Fact Sheet. University of Nevada Cooperative Extension, 3(43), 3–6.

Whitfield, J.B. and Purcell, A. H. III (2012). Daly and Doyen’s introduction to insect biology and diversity (3^th ed.). Oxford, England: Oxford University Press.