Kansas State University


Extension Entomology

Tag: insecticides


–by Dr. Raymond Cloyd

Now is the time to be on the lookout for the elm leaf beetle, Pyrrhalta luteola, which may feed on all elms; however, elm leaf beetle prefers Siberian and American elm, with Chinese elm being less susceptible. Adults are about 1/4-inch long, slender, and yellow-green in color, with black stripes extending down the entire length of the abdomen. Furthermore, there are distinct black spots on the head and thorax. Adults appear in spring and eat small holes in leaves. Females lay yellow-orange eggs in clusters on leaf undersides. A single female can lay between 600 to 800 eggs during her lifetime. Eggs hatch in 5 to 6 days into green larvae that look-like grubs. Larvae are approximately 3/8 to 1/2 inches in length. Initially, they are black, and then turn yellow in color with two black lateral stripes along the sides of the body. Larval feeding causes leaves to appear skeletonized because they scrape the leaf tissue from the upper surface with their chewing mouthparts; leaving the veins intact. The tissue between the veins eventually turns brown. Larvae, which are the major source of damage to plants, feed for about 3 weeks.





The last larval instar crawls down tree trunks, where they pupate at the base of trees in and on the ground. They may also pupate in the cracks and crevices of the trunk or in large branches. In about two-weeks, adults emerge and start feeding on plant leaves. They normally feed on the same trees that larvae fed upon. Adults may be a nuisance pest in late summer and early fall when they migrate from trees and enter homes to overwinter. They will also overwinter in protected places outdoors. It is interesting to note that both adults and larvae may be present simultaneously. There are two generations per year in Kansas with the second generation causing the most damage.



Insecticides should be applied at the first appearance of both adults and larvae, and routinely throughout the summer and early fall in order to protect elm trees. This is especially the case if extensive feeding by elm leaf beetles will impact the aesthetic appearance of elm trees. When using contact insecticides, it is important to obtain thorough coverage of both the underside and upper side of plant leaves. However, avoid applying acephate (Orthene) on American elms as this may cause plant injury. If elm leaf beetle populations are minimal, then insecticide applications may not be warranted. Always read the insecticide label prior to making any applications.

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.


Rose Sawflies

–by Raymond Cloyd

There are at least two species of sawflies that attack roses during this time of year; the rose slug (Endelomyia aethiops) and bristly rose slug (Cladius difformis). Rose slugs are the immature (larval) stage of sawflies, which are black to yellow-colored wasps.

Rose sawfly females make pockets or slits along the edges of rose leaves using their saw-like ovipositor (egg-laying devise), and insert individual eggs. Eggs hatch into larvae that look-like a slug. Larvae are 1.2 cm in length when fully grown and yellow-green in color, with an orange head (Figure 1). The larvae eventually fall on the soil surface to


pupate. Rose slugs overwinter as pupae in earthen cells created by the larvae. There is usually one generation per year in Kansas. Bristly rose slug larvae are pale-green in color and 1.5 to nearly 2.0 cm long. The body is covered with numerous bristle-like hairs (Figure 2). There is generally one generation per year in Kansas.



Rose slug larvae feed on the underside of the leaf resulting in the leaves having a skeletonized appearance (Figure 3), eventually they create notches or holes on the leaf margins. Bristly rose slug larvae feed on the leaf undersides and also cause leaves to appear skeletonized (Figure 4). However, the larvae may chew larger holes than the rose slug.


Small infestations of either the rose sawfly or bristly rose slug can be removed by hand and subsequently placed into a container of soapy water. A forceful water spray will quickly dislodge sawfly larvae from rose plants; consequently, sawfly larvae are not able to crawl back onto rose plants. A number of contact insecticides (various active ingredients) may be effective in suppressing populations of both sawflies. However, the bacterium, Bacillus thuringiensis subsp. kurstaki (sold as Dipel or Thuricide) will have no activity on sawflies as this compound only works on caterpillars.




Feeding Capabilities/Capacities of Caterpillars – Useful Information for Bagworm Control

–by Dr. Bob Bauernfeind

The following basic developmental sequence is applicable to caterpillars regardless their species.

Beginning at egg hatch as a 1st instar larva, a caterpillar progresses through a series of developmental instars until such time it has matured, after which it ceases feeding when ready to transform into its pupal stage. In this sequence as determined under controlled conditions, the variegated cutworm consumed 442.2 mg of artificial diet. Only a small portion (27%) of the diet was consumed through the first 6 instars. In real situations where larvae feed on plant foliage, “nibblings” go unnoticed and are inconsequential. People usually first become aware of the presence of foraging caterpillars as foliage rapidly disappears when caterpillars ravenously feed midway-towards-the-end of their final “chow hound” instar. The last instar consumed 73% of the total diet.

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How can this information be applied to bagworm control? In the following sequence, in Weeks 1 – 5, under the green “safe” line, bags and bagworms are small. At 6 and 7 weeks, they become larger but remain under the yellow “still safe” line. Beginning at weeks 8 and 9, we have the orangish “amber alert” line. To this point, ALL ARE NIBBLERS! In weeks 10 and 11, we are under the red “danger” line as the bagworms now are into their “CHOWHOUND MODE”!

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When bagworms hatch in any given year, the hatching period occurs over a 4 to 5 week period typically beginning in mid-to late May. While it is informative to know when bagworm activities begin, that should not signal the beginning of automatic weekly spray treatments. Rather, a single thorough treatment (with a contact insecticide) applied at the end of June into the first 10-14 days of July should suffice. I enlarged and bolded thorough to emphasize the importance of not merely hastily-applying a light spritzy/misty spray treatment. While such might eliminate bagworms on the periphery of a tree/shrub, bagworm populations located in the more dense inner regions will be least affected. And as insecticide residues dissipate/degrade on the outer foliage, the unaffected bagworms will eventually move out and feed unfettered.

Comes the question regarding product/insecticide-of-choice. Currently in Kansas, there are 400+ products registered for use on bagworms. I personally do not recommend any one product over another. Use any contact insecticide (locally available through retail outlets) with bagworms listed on the product label. Based upon my experiences/trials (the first dating back to 1989), I achieved near-equally effective kill against late-instar bagworms using discontinued active ingredients (chlorpyrifos, diazinon, dimethoate, parathion) as well as currently available acephate, bifenthrin, carbaryl, cyfluthrin, gamma-cyhalothrin, malathion, permethrin, spinosad and trichlorfon. Reemphasizing: what is critical/key is not the active ingredient but rather (again) THOROUGH COVERAGE of the ENTIRE tree/shrub!






Brownheaded Ash Sawfly

–Dr. Raymond Cloyd

We continue to receive inquires throughout the state regarding green ash (Fraxinus pennsylvanica) trees being fed upon by populations of the brownheaded ash sawfly, Tomostethus multicinctus. This is a sporadic, early season, defoliating insect pest that appeared in Manhattan, KS in 2013. Populations feed extensively causing noticeable foliar damage and producing lots of frass (sawfly poop).

Brownheaded ash sawfly larvae, which resemble caterpillars, are 15 to 20 mm long and yellow-green in color with white and green stripes extending the length of the abdomen or back (Figures 1 and 2). They possess a brown head, and have prolegs on every abdominal

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segment with no crochets or hairs on the feet, which distinguishes them from caterpillars. Brownheaded ash sawfly larvae feed primarily on ash trees (green and white) (Figure 3).

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Brownheaded ash sawfly pupates in the spring, with adults, which are wasp-like in appearance, emerging and females laying eggs inside leaves. Eggs hatch into larvae that congregate into massive groups at the base of trees (Figures 4 through 6), and feed from May through June. The larvae create shot-hole or pin-hole damage on leaves when young (Figure 7), but as they increase in size, the larvae consume entire leaves, especially terminal leaves (except the main veins), resulting in almost complete defoliation. The larvae are full-grown by June and shed a paper-like skin that is attached to the leaf (Figure 8). Larvae then migrate toward the base of the tree, enter the soil, and form a protective cocoon. Brownheaded ash sawfly overwinters as a full-grown larvae or pre-pupae within silken-lined cells located in the top portion of the soil at the base of previously infested trees. High numbers may congregate at the base of trees. There is one generation per year.

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In general, it is not warranted to spray an insecticide unless populations of brownheaded ash sawfly larvae are excessive and causing substantial damage to ash trees, which is contingent on the size or age of the tree. It is interesting to note that rainfall will quickly remove larvae from trees. In fact, a forceful water spray will dislodge larvae, which fall to the ground, and then are subsequently consumed by birds. If necessary, insecticides may be applied that contain the following active ingredients: acephate, bifenthrin, carbaryl, cyfluthrin, lambda-cyhalothrin, permethrin, petroleum oil (horticultural oil), potassium salts of fatty acids (insecticidal soap), and pyrethrins. These are all contact insecticides so thorough coverage of the tree canopy is important. Since this insect is a sawfly, insecticides such as Dipel or Thuricide that contain the active ingredient, Bacillus thuringiensis subsp. kurstaki will not be effective (refer to the previous issue of the newsletter). Be sure to assess the numbers of larvae present in order to determine if sufficient damage is occurring to justify the application of an insecticide.





Caterpillars and Sawflies

—Dr. Raymond Cloyd

Caterpillars are the larval stage of butterflies and moths; whereas the larval stage of sawflies is greasy looking and slug-like with the adults resembling wasps. Remember, caterpillars are in the insect order Lepidoptera (butterflies and moths) whereas sawflies are in the order Hymenoptera (ants, bees, and wasps). There are a number of caterpillars and sawflies that feed on horticultural crops. Common caterpillar pests include bagworms, eastern tent caterpillar, fall webworm, mimosa webworm, yellownecked caterpillar, walnut caterpillar, cutworms, European corn borer, and tomato/tobacco hornworms. Sawflies that feed on plants include the European pine sawfly, brownheaded ash sawfly, rose sawfly, and scarlet oak sawfly. Sawfly larvae resemble caterpillars; however, there is a difference.


There are two ways to distinguish between caterpillars and sawflies. First, sawfly larvae have prolegs (stubby-looking legs) on every segment of the abdomen whereas caterpillars are typically missing prolegs. In Figure 1, a caterpillar is on the top and sawfly on the bottom. Second, caterpillar larvae have hairs or crochets on their feet while sawfly larva do not have hairs or crochets on their feet, which is shown in Figure 2, with the caterpillar prolegs on the top and sawfly prolegs on the bottom. Why is it important to know the difference between caterpillars and sawflies? Well, one of the common insecticides recommended for use against young caterpillars is Bacillus thuringiensis subsp. kurstaki that is sold under many trade names including Dipel and Thuricide. This is a bacterium that must be ingested or consumed by the target insect pest, in this case, caterpillars, in order for death to occur. However, the insecticide has no direct effect on sawfly larvae. Therefore, it is important to correctly identify the “caterpillar-like” insect before selecting an insecticide. Specimens may be sent to Kansas State University, Department of Entomology (Manhattan, KS) or the Kansas State University Diagnostic Clinic in the Department of Plant Pathology (Manhattan, KS).