Kansas State University


Extension Entomology

Month: June 2019

Soybean Update – Bean Leaf Beetles and Webworms

— by Dr. Jeff Whitworth and Dr. Holly Davis


Adult bean leaf beetles (BLB) are still causing some concern for soybean producers throughout north central Kansas.  These adults have been chewing round or oval holes in the leaves of seedling plants.  However, it seems much of their leaf feeding has slowed and the females are now mostly on the ground around the base of plants depositing eggs.  These eggs will hatch in a few days and the larvae will start feeding on soybean roots/root hairs.  These larvae resemble corn rootworm larvae but BLB larvae do not feed on corn roots just as corn rootworm larvae do not feed on soybean roots.  One other major difference is that the corn rootworms eggs were deposited in fields planted to corn last year whereas the overwintering adult female BLB deposited these eggs after finding seedling soybean plants this season.

Garden webworms have been causing concern because of visible defoliation over the last couple of weeks.  However, most of these webworms, plus thistle caterpillars, have ceased leaf feeding and are in the process of pupating.  The adults will be emerging over the next couple of weeks and the females will be depositing eggs to initiate the next generation.  Thus, this first infestation of larvae of both species was just a “springboard” generation for the next one or two generations to come.

For more information relative to soybean insect management, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

Mosquitoes: How to Avoid Being “Bitten” by This “Sucking” Insect

–by Dr. Raymond Cloyd

The current wet weather and standing water has provided “perfect” conditions for mosquitoes (Figures 1 and 2). The three primary strategies that must be implemented to avoid mosquito problems and bites are: 1) source reduction, 2) personnel protection, and 3) insecticides.

Fig 1. Mosquito Sucking Blood (Author–Inverse

Fig 2. Mosquito Magnet Sign (Auth–Raymond Cloyd, KSU)

1) Source Reduction
It is important to routinely eliminate or reduce all mosquito breeding sites, which will effectively decrease mosquito populations, by removing stagnant or standing water from items or areas that may collect water. These include the following:
* Wheelbarrows
* Pet food or water dishes
* Saucers/dishes underneath flower pots
* Empty buckets
* Tires
* Toys
* Wading pools
* Birdbaths
* Ditches
* Equipment
* In addition, check gutters regularly to ensure they are draining properly and are not
collecting water

2) Personnel Protection
Protect yourself from mosquito bites by delaying or avoiding being outdoors during dawn or dusk when most mosquitoes are active. Use repellents that contain the following active ingredients: DEET (Figures 3 and 4) or picaridin (Figure 5). Generally, DEET provides up to 10 hours of protection whereas picaridin provides up to 8 hours of protection. A product with a higher percentage of active ingredient will result in longer residual activity or repellency. For children, do not use any more than 30% active ingredient. Furthermore, do not use any repellents on infants less than two months old. Clothing can be sprayed with DEET or permethrin (pyrethroid insecticide). However, be sure to wash clothing separately afterward. Before applying any repellent, always read the label carefully.

Fig 3. DEET Repellents (Auth–Raymond Cloyd, KSU)

Fig 4. DEET Repellent (Auth–Raymond Cloyd, KSU)

Fig 5. Repellent With Picaridin (Auth–Raymond Cloyd, KSU)

3) Insecticides

For stationary ponds, there are several products that may be used, such as; Mosquito Dunks and/or Mosquito Bits (Figure 6). Both contain the active ingredient, Bacillus thuringiensis subsp. israelensis, which is a bacterium ingested by mosquito larvae that results in death. The bacterium only kills mosquito larvae with no direct effects to fish or other vertebrates. Avoid making area-wide applications of contact insecticides because these are generally not effective, and may potentially kill many more beneficial insects and pollinators (e.g. bees) than mosquitoes.

Fig 6. Mosquito Dunks and Mosquito Bits (Auth–Raymond Cloyd, KSU)

What Does Not Work Against Mosquitoes 

The following items will not control mosquitoes:

* Mosquito repellent plants (citronella plants)

* Bug zappers

* Electronic emitters

* Light traps/carbon dioxide traps.

If anyone has questions or comments regarding mosquito control please contact your county extension office or Department of Entomology at Kansas State University (Manhattan, KS).

Special Note: Insect Diagnostician

–by Extension Entomology Team

The Department of Entomology at Kansas State University (Manhattan, KS), currently, does not have an insect diagnostician. Therefore, all physical samples, phone calls, and emails (containing images) regarding arthropods (insects and mites) should initially be handled by the county extension offices. If the agriculture or horticulture agent is unable to identify a specific arthropod, then the agent will contact an extension entomologist at Kansas State University. This process will help expedite identifying samples and addressing inquires.

We sincerely appreciate your cooperation regarding this matter.


Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Davis

Potato leafhoppers are rapidly increasing throughout alfalfa fields in north central Kansas for two reasons:  1) potato leafhopper adults are still migrating in and 2) the eggs are hatching and nymphs seem to be everywhere.  These nymphs are very small and very shy – which means they are easily under counted as they hop to the underside of leaves, or even off the leaves, at the least disturbance.

Alfalfa weevils mating—(photo by T. Sexton)

Parasitized Alfalfa Caterpillar

Alfalfa weevil adults have mostly migrated out of alfalfa fields in north central Kansas, however there are a few that pupated late and that are just emerging out of their pupal cells.  Interesting, at least to us, was that some of these adults were mating (see picture).  Most of the literature reports alfalfa weevils mating in the late summer, fall/winter  —  not soon after becoming adults.

Alfalfa or garden webworms are also relatively common in alfalfa, where they may cause a problem in new alfalfa, and soybeans.  The next generation will probably be more problematic in small soybeans because there will probably be more webworms as this generation is more of a “spring board” generation.

Alfalfa caterpillars (see picture of larva with attached parasitoid eggs) are also quite common in alfalfa fields as are the white and/or yellow butterflies that they develop into.  However, they have not ever been found in densities great enough to cause any negative impact on yield.


Fall Webworm

–by Dr. Raymond Cloyd

The first generation of fall webworm (Hyphantria cunea) is now prevalent in most of Kansas with webs present on certain trees. Fall webworm nests are very noticeable, with silk webbing enclosing the ends of branches and foliage or leaves (Figures 1 and 2).

Fig 1. Fall webworm nest on walnut tree (Auth–Raymond Cloyd, KSU

Fig 2. Fall webworm nest on birch tree (Auth–Raymond Cloyd, KSU

Fall webworm larvae or caterpillars are pale-green, yellow to nearly white, with two black spots on each abdominal segment. Caterpillars are covered with long, white hairs (Figure 3).

Fig 3. Close-up of fall webworm larvae (Auth–Raymond Cloyd, KSU)


Fall webworm caterpillars feed on a wide range of trees, including: birch, crabapple, maples, hickory, pecan, mulberry, and walnut. Fall webworm caterpillars, unlike eastern tent caterpillars, remain within the enclosed webbing and do not venture out to feed. Caterpillars consume leaves, resulting in naked branches with webbing attached that contains fecal deposits or ‘caterpillar poop.’ These nests will eventually dry-up as the caterpillars pupate, with adults’ eclosing (emerging) from pupae later on.


Feeding by fall webworm caterpillars may ruin the aesthetic appeal of infested trees; however, the damage is typically not directly harmful to trees—especially larger trees. The most effective method of dealing with fall webworm infestations is to simply prune-out the webs that enclose the caterpillars, place into a plastic bag, and dispose of immediately. Insecticide sprays may not be effective because the caterpillars remain in the webbing while feeding; thus reducing exposure to spray residues. If insecticides are used, be sure to use high-volume spray applications that penetrate the protective webbing, or use a rake to disrupt or open-up the webbing so that the insecticide spray contacts the caterpillars.



Soybean Update – Thistle Caterpillars and Bean Leaf Beetles

–by Dr. Jeff Whitworth and Dr. Holly Davis

                Thistle caterpillars are becoming more evident around north central Kansas as they increase in size and their feeding becomes more visible.  These larvae are the result of eggs deposited by painted lady butterflies that migrated back into the state about two weeks ago.  These larvae will pupate in a couple of weeks and the adults will emerge soon after.  There will probably be even more in the next generation.



Round and/or oblong holes in seedling soybeans are indicative of adult bean leaf beetle (BLB) feeding.  Remember, these young plants are very resilient at overcoming up to about 50% defoliation in these early vegetative stages.  It takes approximately seven adult BLB/row ft. to achieve that level of defoliation.  However, adult BLB usually don’t feed for more than a few days after locating the seedling soybeans.  While this feeding can cause considerable concern because of the highly visual holes, it typically does not result in much stress to the plants, especially under good growing conditions.


For more information on bean leaf beetle biology and management, please see Bean Leaf Beetle:  https://www.bookstore.ksre.ksu.edu/pubs/MF2824.pdf

For more information relative to all soybean pests, please see the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf


Corn Update – Corn Rootworms and “Ragworms”

–by Dr. Jeff Whitworth and Dr. Holly Davis

Corn rootworm larvae continue to be very active in fields of continuous corn that have been planted to susceptible varieties.

Corn earworms have been feeding in north central Kansas corn for about a week now and signs of this feeding are now becoming visible as the leave start growing out of the whorl.  The small larvae may consist of corn earworms, fall armyworms, and/or armyworms, but all may cause the same type of ragged looking leaves, earning them the name “ragworms”.



This type of leaf feeding can be highly visible, and many plants can be impacted, but the data has always indicated there is little to no effect on yield.  In addition, the larvae are well sheltered within the whorl and thus insecticides only impact them when they exit the whorls to pupate in the soil.  And, by that time, all the feeding is completed anyway.

Alfalfa Update – Potato Leafhoppers and Pea Aphids

–by Dr. Jeff Whitworth and Dr. Holly Davis

Alfalfa seems to be growing very well and many fields around north central Kansas have finally dried out enough to swath and remove the hay from the field.  However, potato leafhoppers continue to migrate into the state and will continue to for about another month.  Most are still adults and have been/are now depositing eggs in stems and the tiny nymphs are just starting to emerge.  Thus, potato leafhopper feeding will become more evident as “hopper burn”, the yellowing of leaves which can reduce the health of the plants and the nutritive value of the foliage.  Therefore, if fields were just recently cut, or will be in the near future, while potato leafhoppers are still migrating into the state, they will be very vulnerable to potato leafhopper feeding damage.

Pea aphids are still plentiful throughout alfalfa fields in north central Kansas.  Populations should not reach treatable levels this late in the year, and they are a good host for many beneficial insects.

For more information regarding these and other alfalfa pests, please see the KSU Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf