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How the Beet (Armyworm) Goes On

Agricultural Research Service scientists in Weslaco, Texas, are researching what the beet armyworm prefers when it comes to picking a host plant for its offspring.

Entomologists Shoil Greenberg, Allan Showler and Thomas Sappington have spent the past several years determining the factors behind beet armyworms' decisions. They're based at the ARS Kika de la Garza Subtropical Agricultural Research Center in Weslaco.

According to Sappington, it is well documented in literature that pigweed, cotton, peppers, sunflowers and cabbage, among other species, are used as host plants by beet armyworms. But the pests have their preferences, even among these host plants, the scientists report.

During lab experiments on individual leaves and in greenhouse studies using potted plants, female beet armyworms laid eggs four to five times more often on pigweed than on sunflower or cabbage, according to Sappington. Cotton and peppers were an intermediate choice, receiving only half as many eggs as pigweed.

Greenberg and Sappington, in parallel studies, found that beet armyworm larvae thrived better on pigweed. The insects grew faster and larger than larvae from eggs laid on cotton or peppers.

Showler looked at egg-laying choices when the insects were limited to using their sense of smell to identify a preferred host plant. Working on smell alone, the females laid more than three times more eggs on pigweed than on cotton plants.

Showler knew from other studies that pigweed provides a nutritional advantage to beet armyworm larvae. He found that pigweed has much higher free amino acids levels than other host plants and a more diverse array of them. Unlike proteins, free amino acids don't have to be broken down before they can be used by the insect.

Showler has found in pigweed nine of the 10 free amino acids that can provide a nutritional advantage to insects, and the tenth one may be there as well.

ARS is the Department of Agriculture's primary scientific research agency.