Rednecked Peanutworm: New Guide Examines Management Options for Peanut Pest

By Odair Aparecido Fernandes, Ph.D.

The rednecked peanutworm (Stegasta bosqueella) is the main lepidopteran pest in South and Central American peanut fields. It can be differentiated from S. capitella, another caterpillar pest of peanut plants, by dark brown coloration of its head and thorax, which is descriptive of its common name. On the topic of names, the species name was misspelled for years in the literature, at times both as basqueella and bosquella, and the latter of those incorrect names is still more cited that the now agreed-upon bosqueella.

In a new profile published this month in the open-access Journal of Integrated Pest Management, my colleagues and I revisit the history of classification, life history, biology, ecology, management options, and need for enhancing the current control strategies of S. bosqueella.

The rednecked peanutworm adult can lay up to 230 eggs singly or in small groups on the peanut plant stem. After hatching, the larva moves toward the closed leaflets, where it remains sheltered as it feeds through five instars until it either pupates on the plant or falls into the soil to pupate. Damage to peanut plants by larvae affects the production of new shoots, pegs, and pods and reduces the overall development of plants, which may lead to yield loss when population densities are high. Although it is an important defoliator in some peanut producing countries, there is scarce information on some aspects of the biology as well as plant response to this insect species.

At this time, chemical control is the main tool used to control larval infestations. In some countries the use of insecticides is associated with fungicides due to susceptibility of peanut varieties to several phytopathogens. Calendar-based applications of products to control insects, including the rednecked peanutworm, are very frequently adopted under these circumstances. Some of the issues with chemical reliance include insecticide resistance.

The rednecked peanutworm (Stegasta bosqueella) is the main lepidopteran pest in South and Central American peanut fields. The rednecked peanutworm adult (such as shown here) can lay up to 230 eggs singly or in small groups on the peanut plant stem. (Photo by José Ricardo Lima Pinto)

These damaged peanut leaves show typical injury caused by the rednecked peanutworm (Stegasta bosqueella). The larvae feed the leaflets while they are still closed. After the leaflets open, they commonly present a symmetrical injury pattern. (Photo by Odair Aparecido Fernandes, Ph.D.)

Our research explores different types of host-plant resistance including antixenosis, antibiosis, and tolerance, which may help reduce pressure on peanut plants. We also discuss biological control tactics (using natural enemies such as parasitoids and entomopathogenic microorganisms) as well as attract-and kill strategies to reduce the reliance on chemical control. These tactics were promising and may be useful to enhance a peanut integrated pest management program for regions struggling to control rednecked peanutworm in peanut production. If resistant peanut varieties to fungi diseases are developed, reducing the need to regularly apply fungicide and subsequently insecticides, IPM would be more easily adopted.

Economic threshold levels are not yet well established and, consequently, decision making is compromised. Therefore, a better understanding of population dynamics and peanut response to injury caused by rednecked peanutworm are necessary next steps to protect peanut plants in high pest prevalent regions.

Odair Aparecido Fernandes, Ph.D., is a professor in the Department of Agricultural Production Sciences at São Paulo State University in Brazil. Email: odair.fernandes@unesp.br.