Alligatorweed Thrips for Alligatorweed Control

— Written By

There is a new to North Carolina management strategy for alligatorweed control. Alligatorweed (Alternanthera philoxeroides) is an invasive aquatic weed native to Brazil that arrived in the southeastern US in the early 1900s. The plant has opposite leaves, a hollow stem, and a white clover-like flower. It grows very well in our ditches, ponds, and waterways.

alligatorweed

Healthy alligatorweed with distinctive white clover-like flowers. Photo by D. Rashash

The plant spreads through fragmentation, with each node capable of forming a new plant. So, weed whacking ditches with alligatorweed is NOT recommended! Typical chemical control measures have included the use of glyphosate applied at regular intervals throughout the growing season.

From 2006-2015, several counties in eastern NC received Alligatorweed flea beetles (Agasicles hygrophila) in hopes that they would be a useful integrated pest management (IPM) practice. Unfortunately, NC is at the northern edge of their cold tolerance. Despite repeated attempts, strong colonies of the alligatorweed flea beetles were not attained.

In August 2018, a sample of “sick” alligatorweed from a pond in Onslow County was sent to the NC State University Plant Disease & Insect Clinic (PDIC) and the Army Corps of Engineers lab in Vicksburg, MS. Both laboratories confirmed the presence of alligatorweed thrips (Amynothrips andersoni O’Neill). The adult a. thrips is approximately 2 mm in size, and the larvae are roughly 1.5 mm.

Image of alligatorweed thrips

Adult alligatorweed thrips, Amynothrips andersoni O’Neill. Photo by D. Rashash

Immature alligatorweed thrips image

Closeup of immature alligatorweed thrips. Photo by D. Rashash

This was the first confirmed sighting of alligatorweed thrips in NC. The a. thrips has a broader cold tolerance than the flea beetle. The a. thrips at the Onslow site easily survived the 10-day freezing spell during Winter 2018. This gives us hope that a. thrips will be a good IPM agent. The a. thrips juveniles and adults only eat alligatorweed, so there is no risk to other plants or crops.

Early damage appears as discolored and curled leaves. A high level of predation can completely defoliate a patch of alligatorweed. These are tiny, yet mighty!

Alligatorweed leaf damage caused by alligatorweed thrips

Alligatorweed leaf damage caused by alligatorweed thrips. Photo by D. Rashash

Patch of alligatorweed impacted by alligatorweed thrips.

Patch of alligatorweed impacted by alligatorweed thrips. Photo by D. Rashash

Since their discovery in NC, the alligatorweed thrips have been provided to N.C. Department of Agriculture and Consumer Services, Beneficial Insect Lab. NCDA&CS is establishing a breeding population. N.C. Cooperative Extension Service has placed a. thrips at alligatorweed locations in Brunswick, New Hanover, Onslow, Craven, Hyde, and Camden counties. Steven Turner at NCDA&CS’s Beneficial Insect Lab has placed a. thrips at Apex Lake. Happy alligatorweed munching little guys!

If you see signs of thrips damage to alligatorweed, please contact me at diana_rashash@ncsu.edu. We are trying to determine if there are other locations where these beneficial insects are active.