Amauromyza karli

Order: Diptera
Family: Agromyzidae

Description

Adults of A. karli are approximately 3 mm in length, have a dark brown thorax and abdomen and distinct yellow heads. The flies also have light-yellow halteres (reduced hindwings) and dark brown legs with narrow, yellow ends of the femur and tibia.

Larvae are white and measure around 4.5 mm when fully grown.

Pupae are brown and approximately 2.5 mm in length.

The eggs of A. karli have not yet been observed, but the eggs of other closely related species are white, oval shaped and laid in clusters.

Quick Facts

• This stem-boring fly was recently (2021) discovered in quinoa in the United States.
• In 2021, infestations were present in 100% of quinoa grown in San Luis Valley in Colorado, and either caused severe yield loss or destroyed the crop entirely.
• There are no management recommendations for this pest, however, there are monitoring protocols that can help growers determine whether an infestation is present.

A. karli fly

Adult A. karli
Tim McNary, Colorado State University

Adult A. karli collected from quinoa grown in Alamosa, Colorado. Distinguishing features include a yellow head and dark brown body with light-yellow halteres. The legs are dark brown with yellow ends of the femur and tibia.

A. karli larva

Larva of A. karli collected from quinoa stems grown in Colorado. These larvae feed within the plant stem of quinoa and cause plant death or severe yield losses.
Tim McNary, Colorado State University

A. karli pupa

Ventral view of an A. karli pupa. Most other stem-boring agromyzids pupate outside of the stems, and while pupation habits have not yet been observed in A. karli it is likely that the larvae exit the stems before pupating in the soil as well.
Tim McNary, Colorado State University

Exit hole in quinoa stem

Exit hole in quinoa stem likely caused by larvae of A. karli.
Adrianna Szczepaniec, Colorado State University

Field damage to quinoa

Examples of field damage to quinoa resulting from an outbreak of A. karli.
Patrick O’Neil, San Luis Valley, Colorado

Life History

Little is known about the natural history and habits of A. karli. Many closely related species lay eggs by repeatedly thrusting an egg-laying structure, called an ovipositor, into plant tissue until the eggs are deposited. After hatching, A. karli larvae feed within the stems of quinoa and exit the stems to pupate outside of the plant in the soil. The flies likely have several generations each year.

Injury

Extensive feeding of A. karli larvae destroys the pith and disrupts nutrient transport which causes lodging, reduced yield, and death of the plant. This feeding injury has caused significant declines in quinoa production in Colorado. Upon exit, the larvae create exit holes in the stems.

Monitoring

Monitoring populations of A. karli in quinoa is effectively accomplished through several techniques that help determine the onset of an infestation and the extent of an infestation after A. karli is confirmed. To monitor the adults, yellow sticky traps can be used to capture flies and then identify and count them using a hand lens or a dissecting microscope. Fields can also be surveyed using a sweep net. Once A. karli adults are detected using sticky traps or sweep netting, quinoa stems can be destructively sampled by cutting plants at the base and splitting the stems to examine for the presence of larvae in the pith.

Management

This is an emerging pest, and there are no research-supported recommendations for suppression of A. karli. However, host plant resistance and biological control are likely to emerge as the most effective management tactics. Stem boring insects are difficult to control using insecticides, and combining chemical control with other integrated pest management tactics is likely to be key to suppressing the impact of A. karli on quinoa.