Kansas State University


Extension Entomology

Tag: instar larvae


–by Dr. Jeff Whitworth and Dr. Holly Schwarting

   Alfalfa weevils continue to be very active throughout NC KS. This past week the weevil populations were still plentiful and in all stages, including very small 1st instar larvae. This is really unusual, as we started finding 1st instar larvae back in the 1st part of March. This is really a testament to the fluctuating temperatures that we have seen over the last 2 months, with a relatively warm winter/early spring then a major cool down with several nights of freezing temperatures which have slowed down weevil development significantly. Please remember, if an insecticide application is still warranted, check the Pre Harvest Interval (PHI) for the product of choice.

Alfalfa Weevil Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are still very active throughout north central Kansas.  They also range in development from small 1st instar larvae to relatively mature 3rd instars.

Aw life stages

We have also had reports of pupae in south central and north central Kansas.  Many fields are still showing signs of freeze damage.

freeze damaged field

The freeze did seem to affect the weevils by slowing their development but did not kill them.  However, most larvae in freeze-damaged fields are more yellow than the usual greenish color.  Whether that means they are getting the proper nourishment from the yellowed, freeze-damaged alfalfa tissue or not is unknown.

larvae color difference

Weevil larvae in untreated, non-freeze-damaged fields seem mostly about to pupate within 7-10 days if temperatures stay between 45-80°F.  No other pests have been noted in alfalfa fields we visited over the past week.

Bagworms —- Current Status, and What to Do

–by Dr. Bob Bauernfeind

For the past several weeks, in Ward Upham’s compilation of Hot Topics, bagworms have been mentioned.  Last week, they were designated as Pest of the Week.   This is not a real surprise given the time of the year.  Why?  As pictured below, the colored time frames are indicative of bagworm feeding capabilities.  Smaller (generally overlooked) larvae in the green and yellow zones represent periods when larvae are small “nibblers” — negligible visible feeding damage.

The orangish/amberish represents “caution” — larger larvae becoming more destructive but not necessarily causing noticeable damage.  But now (August) is the red danger zone where (as is typical for all lepidopteran larvae) rapidly growing larvae in their last feeding stages consume the greatest amount of foliage (create the most noticeable damage) that has people reacting to the presence of bagworms.


The question now is, “Is it too late to spray for bagworms?”  Currently, it is not too late to spray!  Notwithstanding their size, as long as bagworms are actively foraging, they can be effectively controlled.  Those directly hit by an insecticide spray will be killed by contact action.  Those withdrawn into their bag at the time of the spray application will likely succumb after coming-in-contact with treated foliage, but most certainly after consuming treated foliage.

How does one determine if bagworms are actively feeding?  OBSERVATION!  “Active bags” can be identified by newly-clipped greenery at the bag opening.  Also, with a bit of patience, simply watch for a bagworm to reopen its bag, poke out its head, and resume feeding.


When is it too late to spray for bagworms?  That also is easily determined.  When a bagworm completes its feeding cycle, it anchors its bag to the host plant with a distinct, highly visible white silken “tie”, after which it permanently closes the “front door”.  Spraying at this point-in-time is futile because the thick leathery bag protects the bagworm within.


According to NPIRS (National Pesticide Information Retrieval System), currently in Kansas, there are 500 products registered for use against bagworms.  Some active ingredients currently contained in insecticides available for purchase and use by homeowners include acephate, Bacillus thuringiensis, bifenthrin, carbaryl, cyfluthrin, cyhalothrin (gamma and lambda), deltamethrin, malathion, permethrin and spinosad.  In various trials, I have used the bolded AIs and found them all to be effective against bagworms, even those considered large and close to the end of their feeding cycle.  Some homeowners may still be in possession of discontinued products with the active ingredients chlorpyrifos, dimethoate and/or diazinon.  All were effective against bagworms in trials.  Although it does not appear to have been written into any legalized directive (per personal communication with the KDA), discontinued products may still be used if done in accordance with the instructions appearing on the product label.  Residents may not share or give partial containers to neighbors as this would be considered distribution.

Excluding products containing Bacillus thuringiensis (minimal effectiveness against larger instar larvae), regardless of which product/AI is applied, the critical factor for successful bagworm population reduction is THOROUGH COVERAGE TOP-TO-BOTTOM!  Hastily applied light/misty sprays to tree and shrub peripheries will lead to disappointing results.


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