Sesame Leafroller / Sesame Webworm

For a few years Sesame grown in the Valley had few insect pests and populations typically stayed well below management thresholds.  Unfortunately, this has been changing over the past few years and we are starting to see several insects cause significant problems here and there. 

One of these is the sesame leafroller, also called the sesame webworm or sesame capsule borer, Antigastra catalaunalis.  It is a type of Crambid or snout moth.  The adults are a cream to brownish moth with a wingspan of a little over ½ inch.  Forewings have  zigzag lines while the hind wings are solid pale yellow.  Adults feed on plant nectar, live around 1 week and spend this time mating and locating host plants where the female will oviposit, or deposit eggs, singly on the underside of sesame leaves. 

Sesame leafroller adult

Eggs hatch in 2-3 days and larvae immediately begin feeding.  These tiny larvae (0.1 cm long) will feed for 10-12 days, going through five instars, or molts, before reaching larval maturity.  As larvae grow, they become yellowish to green with black spots and have a dark brown to black head capsule.  Mature larvae will reach 1 to 1.5 cm in length.

Showing two instars of leafroller larvae

Sesame leafroller larvae (Photo by Danielle Sekula)

Larvae are the damaging stage and feed on tender foliage, pods, and shoots.  As their name suggests, they web the top leaves and terminal portion of the plant to provide a protected location where they will feed, often destroying the apical meristem of the plant. 

The damage is easy to detect and is often full of little black balls of frass, or excrement.  If you pull this webbing apart, you will find one or more larvae feeding.  In many cases they can be seen between the stem and pods where they bore holes into the developing pods and destroy the seeds inside. 

Showing webbing and feeding damage by sesame leafroller

Feeding damage to seed pod/capsule

Once larval feeding is complete, they will pupate inside webbed leaves, or may drop to the ground and pupate in the soil.  Pupation lasts 5-6 days when adults will emerge and begin the cycle again.  It is likely there will be at least several generations in the Valley so sesame developing at different times can be infested.

Sesame leafroller pupa between stem and capsule

We do not have a lot of information on control of this pest in Texas.  Studies done worldwide have suggested that earlier planted sesame may not experience as high of levels of infestation as later planted sesame.  This may be because several generations have built up resulting in larger populations later in the season.  However, we have no data to show that this is the case in South Texas.  This insect does have other reported hosts including Amarathus species meaning it will have alternative hosts when sesame is not available, and thus weed control may aid in keeping webworm populations down.

We do not have established thresholds for this pest.  However, because they are feeding directly on flowers and pods, relatively low populations can likely cause significant yield loss. 

Insecticide applications are currently the best recommendation for control.  There are relatively few insecticides labelled for use in sesame at this time. When spraying for this pest, keep in mind that while they are often on the tip of the plant, they are also protected in webbing.  For this reason, contact insecticides will require plenty of carrier and good pressure to penetrate webbing and get the insecticides to where larvae are feeding. Growers and consultants have reported that an application of Chlorantaniliprole has provided good control of this pest.