Apple curculio: A lesser-known orchard pest

Madeline Wimmer- UMN Fruit Production Extension Educator

Images: Historical drawings of the apple curculio (Anthonomus quadrigibbus) that were incorporated into a 1928 article in the Journal of Agricultural Research, “The apple curculio and its control by hogs.” The left drawing was labeled, “Adult apple curculio,” showing adults feeding and ovipositing, or laying eggs during the spring; and the second image is labeled, “Fallen apple from which an adult apple curculio has escaped, and cut apple showing pupa,” because apple curculios pupate within apple fruits.

When thinking about curculios, the first pest that might come to mind is the plum curculio (Conotrachelus nenuphar). However, there is a second curculio pest that is lesser known and less commonly experienced as an orchard pest: the apple curculio (Anthonomus quadrigibbus). Apple curculios and plum curculios are both in the curculionidae family. While they share some similar characteristics and habits, the two pests are very different. In this article, we’ll review the apple curculio’s appearance, life cycle/habits, and management considerations, followed by a detailed chart at the end comparing apple and plum curculios. By the end of this article, you might be able to reflect on whether you've only seen plum curculios in your orchards or if perhaps the apple curculio has also been present.

Identification

Images: The apple curculio (left; photo by M.J. Hatfield, 2021) can be uniquely identified by its reddish brown colors and long snout, which differs from the appearance of the plum curculio (right; photo by John R. Maxwell, 2010).

Apple curculios are reddish-brown, about 5 mm in length, with two sets of knobs on their wing covers (i.e., elytra), and a long, protruding snout. This contrasts the plum curculio, which is known for having a shorter, drooping snout, four pairs of knobs on its wing covers, and exhibits a brown, black, and light gray mottling pattern.

Hosts, lifecycle, and damage

Images: Apple curculios can cause damage to apples when they pierce the fruit to lay eggs and fill the hole with frass. They additionally damage apples with early and late season feeding. Images originate from the British Columbia Ministry of Agriculture.

Apple curculios share many of the same hosts as plum curculios, but are less likely to affect stone fruits, except tart cherries. The top plants affected by apple curculio are crab and fresh eating apples, pears, quince, and hawthorn.

When apple curculios emerge in the spring, adults will usually travel by flying and can damage tender vegetative growth and blossoms. Similar to plum curculio, adult females oviposit, or lay eggs in developing fruitlets, but they do not leave the crescent-shaped scar signature to plum curculios. Instead, the apple curculio punctures the fruit, lays the egg, and seals the hole with frass. 

After the egg has been laid, affected apples may drop to the ground or remain on the tree. This is another point where the apple curculio’s life cycle differs from plum curculio: as larvae hatch out of eggs within dropped fruits, they will remain within the fruit, pupate, and emerge as adult curculios. Larvae embedded in fruits that remain on the tree are also less likely to be crushed and sometimes end up pupating within fruits on a tree. 

When adults emerge in the late summer they have the ability to continue to feed and cause damage to fruits and foliage. Post late-summer feeding, apple curculios are more likely to stay localized to orchard regions where damage has occurred. This contrasts the plum curculio, which can overwinter in low-managed, or abandoned orchards, but is more likely to seek deeper leaf cover when overwintering.

Management

Very little research has been done in the past on apple curculio and its management. Much of the literature reaches back as far as the early 1900s, including the 1928 paper “The apple curculio and its control by hogs” by B.B. Fulton from Iowa State University (previously named Iowa State College). Within this paper, encouraging hogs to eat apples from the ground between mid-June until mid-July showed some management for apple curculio populations. This likely worked because apple curculio not only feeds as a larva on dropped fruits, but spends extra time pupating within the fruit. Even without hogs, orchards dealing with apple curculio may want to harvest and destroy fruits from the orchard floor to remove pupating populations and disrupt the apple curculio life cycle.

In regards to chemical management, it is likely that there is some cross coverage between those insecticides that target plum curculio, or even other insect pests, and what controls apple curculio, but this presumption would likely vary depending on the insecticide and its mode of action.

Should you be concerned about apple curculio?

Apple curculio is considered an occasional pest of apples. Peter Werts, who specializes in specialty crop production for the IPM Institute, noted seeing apple curculio at three out of twenty orchards he visited in 2024. He additionally has mentioned that when he sees apple curculio, it is usually in orchards where there is a delay in applying insecticides after petal fall. Therefore, it is possible that many insecticides used for plum curculio and other insect pests after petal fall could also manage apple curculio. There are many valid reasons why growers may want to delay insecticide applications after petal fall; thus, finding alternative management methods that go beyond recommending earlier sprays would be beneficial.

One final note

While delta traps commonly used for plum curculio monitoring may end up catching some apple curculios, it is more likely that flying adults will be caught on yellow sticky cards. The next time you come across curculios in either trap, take a moment to look at them with a hand lens. Are you seeing apple curculios in your orchard?

 References:

1. British Columbia Ministry of Agriculture. 2020. Apple Curculio.
2. Brooks, Fred E., Three beetles that attack apples: Plum curculio, apple curculio, and apple weevil, 1936.
3. Deutsch, A. & Guedot, C., Plum Curculio, UW Extension, 2018.
4. Fulton, B.B. The apple curculio and its control by hogs, Journal of Agricultural Research, Volume 36, No. 3, 1 February 1928.
5. Jeger, M. et. al., Pest categorization of Anthonomus quadrigibbus. EFSA Panel on Plant Health. 12 April 2018.
6. Maier, Chris T., Native and Exotic Rosaceous Hosts of Apple, Plum, and Quince Curculio Larvae (Coleoptera: Curculionidae) in the Northeastern United States, Journal of Economic Entomology, Volume 83, Issue 4, 1 August 1990, Pages 1326–1332, https://doi.org/10.1093/jee/83.4.1326
7. Whalon, M. et al., Plum curculio management and spray timing, Michigan State University Extension, 2007.