Kansas State University

search

Extension Entomology

Tag: feeding

Bagworms are Here!

–by Dr. Raymond Cloyd

Bagworms are Here!

Now is the time to start taking action against that “infamous” insect pest known as the bagworm (Thyridopteryx ephemeraeformis). Throughout Kansas, bagworm eggs have hatched and the young caterpillars are feeding on both broadleaf and evergreen trees and shrubs. Bagworms are primarily a pest of conifers but have expanded their host range to include a number of broadleaf plants, including: rose, honeylocust, and flowering plum. Hand-picking small caterpillars (along with their accompanying bag) and placing them into a container of soapy water will kill them directly. This practice, if feasible, will quickly remove populations before they can cause substantial plant damage.

For those not interested in hand-picking, a number of insecticides are labeled for use against bagworms including those with the following active ingredients (trade name in parentheses): acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel/Thuricide), cyfluthrin (Tempo), lambda-cyhalothrin (Scimitar), trichlorfon (Dylox), indoxacarb (Provaunt), chlorantraniliprole (Acelepryn), and spinosad (Conserve). Many of these active ingredients are commercially available and sold under different trade names or as generic products. However, several insecticides may not be directly available to homeowners. The key to managing bagworms with insecticides is to apply early and frequently enough in order to kill the highly susceptible young caterpillars that are feeding aggressively on plant foliage (Figure 1). Older caterpillars that develop

 

Figure 1. Young Bagworm Feeding On Conifer (Author-Raymond Cloyd, Kansas State University)

 

later in the season (Figure 2) are typically more difficult to kill with insecticides. Furthermore, females feed less as they prepare for reproduction, which reduces their susceptibility to spray applications and any residues. The bacterium Bacillus thuringiensis subsp. kurstaki is active on young caterpillars; however, the active ingredient must be consumed to be effective, so thorough coverage of all plant parts and frequent applications are required. This compound is sensitive to ultra-violet light degradation and rainfall, which reduces residual activity. Spinosad is the active ingredient in a number of homeowner products, including: Borer, Bagworm, Tent Caterpillar and Leafminer Spray; Captain Jack’s DeadBug Brew; and Monterey Garden Insect Spray. These products work by contact and ingestion (stomach poison) although they are most

 

Figure 2. Older Bagworms (Author-Raymond Cloyd, Kansas State University)

 

 

effective when ingested and can be used against older or larger bagworm caterpillars (Figure 3). Cyfluthrin, lambda-cyhalothrin, trichlorfon, chlorantraniliprole, and indoxacarb may be used against both the young and the older caterpillars. However, thorough coverage of all plant parts, especially the tops of trees and shrubs, where bagworms commonly initiate feeding, and frequent applications are required. The reason multiple applications are needed when bagworms are first detected is because young bagworms “blow in” (called ‘ballooning’) from neighboring plants on silken threads. If left unchecked, bagworms can cause significant damage, and ruin the aesthetic quality of plants. In addition, bagworms may actually kill plants, especially newly transplanted small evergreens, since evergreens do not usually produce another flush of growth.

 

Figure 3. Captain Jack’s DeadBug Brew (Author-Raymond Cloyd, Kansas State University)

If you have any questions regarding the management bagworms contact your county horticultural agent, or university-based or state extension entomologist.

 

 

European Pine Sawfly

–Dr. Raymond Cloyd

Yesterday (April 17, 2017) European pine sawfly, Neodiprion sertifer larvae were detected feeding on my “indicator pine” in Manhattan, KS (I was totally excited!). Young caterpillar-looking larvae are 1/4 inch in length and olive-green in color with a black head (Figures 1). Mature larvae are >1.0 inch long with green stripes. The larvae are gregarious or feed in groups on needles of a variety of pines, especially Scotch, red, and mugo pine. When disturbed, each individual larva will arch their head and abdomen (last segment of an insect body) back, forming a “C-shape” (Figure 2), which is a defensive posture to ward-off predators.

Figure 1. Young European Pine Sawfly Larvae

Eventually, larvae will strip the needles of mature foliage, leaving only the central core, which is white and then turns brown (Figure 3). In general, larvae complete feeding by the time needles emerge from the candelabra. Therefore, those really is only a minor threat of branch or tree death resulting from sawfly larval feeding. However, the loss of second- and third-year needles will be noticeable in landscape trees; thus ruining their aesthetic appearance. In late spring, larvae drop to the ground and pupate in brown, leathery cocoons located at the base of trees. Adults, which are wasp-like, emerge in fall and lay eggs in needles prior to the onset of winter. There is one generation per year in Kansas.

Figure 2. European Sawfly Larvae In A Defensive Posture (Arching Head And Abdomen Back)

Sawfly larvae look-like caterpillars; but, they are not caterpillars (Order: Lepidoptera). Sawflies are related to ants, bees, and wasps (Order: Hymenoptera). The primary way to distinguish a sawfly larva from a caterpillar is by the following: 1) sawfly larva have prolegs (fleshy abdominal legs) on every abdominal segment whereas caterpillars are missing prolegs on the abdomen and 2) caterpillar larva have hairs or crochets on their feet whereas sawfly larva do not have hairs or crochets on their feet.

Figure 3. Feeding Damage To Pine Caused By European Pine Sawfly Larvae

Sawfly larvae are not caterpillars, therefore, the bacterial insecticide, Bacillus thuringiensis subsp. kurstaki (sold as Dipel) will not directly kill sawfly larvae. Dealing with sawfly larvae involves hand-picking (you can wear gloves if you wish) or dislodging larvae from plants by means of a forceful water spray. If necessary, there are a number of insecticides that may be applied to suppress European pine sawfly populations including: acephate (Orthene), azadirachtin, carbaryl (Sevin), spinosad (Captain Jack’s DeadBug Brew and Conserve), and any pyrethroid insecticide (e.g., bifenthrin, cyfluthrin, and lambda-cyhalothrin). Be sure to read the insecticide label to make sure that sawflies are listed. For more information regarding European pine sawfly management contact your county or state extension specialist.

 

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevil feeding activity has slowed significantly in north central Kansas, at least south of I-70.  North of I-70, larvae are still developing and thus feeding, but even in the northern counties this feeding and resultant damage should be significantly reduced by the end of the next week.  There are still some small larvae but the majority of populations are pupating or have pupated.  Adult weevils are still hanging out in alfalfa fields and probably will until that 1st cutting, or temperatures get into the mid-80’s or warmer.

Alfalfa Update

–by Dr. Jeff Whitworth, Dr. Holly Schwarting & JR Ewing

Alfalfa weevil larvae have been hatching throughout north central and south central Kansas for the last couple of weeks.  However, as of 9 March, there doesn’t seem to be much feeding or development yet (Photo1).  There are also a few of these tiny larvae that are dead (Photo2).  Because these larvae are so small and vulnerable it is difficult to determine the cause of death.  At least some of the mortality could be related to weather fluctuations that have reached mid 70’s for several days but also dropping into the mid to low 20’s some nights.

 

 

 

Most of these larvae are so small that they are well enclosed within the plant terminals to the point that they cannot be dislodged by shaking the stems into a bucket, as the most accurate sampling method specifies.  This can definitely cause you to underestimate larval populations.  Probably the easiest solution is to hold off sampling until the middle of next week, if the weather turns cooler as predicted.  There are a few more mature larvae present, along with adult weevils (Photos 3, 4). Adults will probably continue depositing eggs for a few more weeks, thus extending the period of larval hatching.

 

 

There are also a few pea aphids present.  Populations do not seem to be increasing now, and there are lady beetles and parasitoid wasps actively attacking these aphids.  Also, reports of cowpea aphids in south central Kansas bear watching.  These aphids are usually more numerous in warmer summer months.  They can add stress to plants by feeding, but they also produce copious quantities of honeydew which can become covered with sooty mold.  This may further stress alfalfa by interfering with photosynthesis, especially with small plants coming out of winter dormancy and experiencing dry conditions and fluctuating temperatures.

 

 

 

 

Alfalfa weevil status

–Jeff Whitworth, Extension Entomologist: Holly Schwarting, Entomology Research Assoc.; Steve Watson, Agronomy; Mary Knapp, Weather Data Library

Thanks to the unusually warm winter, alfalfa weevil larvae are already present in some areas. Many more will no doubt be hatching in the next few days to weeks. Alfalfa weevils will continue to hatch and larvae continue to develop any time temperatures exceed 48°F.

 

Thus, it looks like larvae will be emerging, and damage progressing, relatively quickly. Whether this warm weather will compress the alfalfa weevil larval feeding so that the period of damage is not as stretched out as usual remains to be seen. There are also lady beetles active in the alfalfa fields, as well as a few pea aphids. The treatment threshold we use for alfalfa weevil insecticide applications is 30-50% infestation, i.e. 1 larva/2-3 stems.

 

Alfalfa weevils are cool-weather insects. Adults lay eggs in alfalfa fields in the fall or even the winter. Most of these eggs survive the winter. Eggs hatch and larvae emerge after accumulating enough degree days or thermal units, normally in early spring. Alfalfa weevil adults also lay eggs in the spring, but in many cases the first larvae to emerge are from eggs that were laid in the fall and overwintered.

 

That said, an anomaly we encountered in the fall of 2016 was a significant infestation of relatively large (2nd and 3rd instar) larvae from mid-November to mid-December. Alfalfa weevils normally overwinter as eggs or adults – not larvae. In the last week we could find none of these more mature larvae, or any pupae. So, hopefully they perished in the colder weather.

Figure 1. Alfalfa weevil larvae collected Nov. 16, 2016 in Dickinson Co.

 

 

Figure 2. Alfalfa weevil larva collected Feb. 22, 2017 in Dickinson Co.

However, as of February 22 we did start finding newly hatched larvae in north central Kansas (Figure 2). Obviously the larvae hatching out now are coming from eggs deposited prior to Jan. 1, 2017. The return of below freezing temperatures may kill those very small, young larvae, especially if they stay in the plant terminals. But, they may survive if they crawl down the plant and get in the plant residue where they will be protected. So, scouting should continue as follows:

 

 

Early scouting for alfalfa weevil

 

Scouting for alfalfa weevil larvae should start after plants break dormancy – which means now. A degree day or thermal unit accumulation system can be used to predict when to initiate scouting. Insect development is controlled by temperature. This can be used to help manage these pests. Weevil activity has been tracked in Kansas for the past few years and has been used to generate recom­mendations (Table 1).

 

 

Table 1. Approximate degree days required for alfalfa weevil development

Degree Days or Thermal Units Stage Importance
25–300 Eggs develop and hatch In stems
301–450 1st and 2nd instars Leaf pinholing – start sampling
450–600 2nd and 3rd instars Defoliation
600–750 3rd and 4th instars Defoliation
750+ Pupa to adult Adults – some feeding – oversummering

 

To calculate a degree day, record the daily high tempera­ture anytime it exceeds 48ºF. For example, if there is only one day in January that the temperature exceeded 48ºF, take that temperature and add the lowest temperature for that day, or 48ºF, whichever is higher. Then divide by 2 to calculate the average tempera­ture for that day. Next, subtract 48ºF.

As an example, say there was one day in January when the high temperature was 60ºF and the low was 35ºF. You would use 48ºF as the default value for the low instead of 35ºF. The calculation in this case would be:

[(60 + 48)/2] – 48 = 54 – 48 = 6 degree days (or weevil development units)

 

The following chart from K-State’s Weather Data Library shows examples of the degree days that have accumulated for the period for Jan. 1 – Feb. 21, 2017 and for last fall:

 

 

Do not be too quick to treat for alfalfa weevil. Wait until the field reaches the treatment threshold. Treating too early is not only unnecessary, it can also have detrimental effects by killing beneficial insects.

 

For more details, see Alfalfa Weevils, K-State publication MF-2999, at your local county Extension office, or http://www.bookstore.ksre.ksu.edu/pubs/MF2999.pdf

 

 

Other early spring alfalfa insects

 

While scouting for alfalfa weevils, you will probably also notice a few pea aphids. These are also early season potential pests. However, in the past few years pea aphids have seemed to be adequately controlled by adult lady beetles. This year seems to be starting that way as well, with a few pea aphids, but also many adult lady beetles present.

Figure 3. Pea aphid on alfalfa leaf.

 

Also, producers need to keep an eye out for army cutworms as there were some reports of army cutworm activity last fall. Army cutworms start feeding again any time temperatures are above 50 degrees F. Armyworms are another potential problem, but probably a little later in the spring.

 

Those are the early season pests which have the most potential for damaging alfalfa prior to the first cutting. For more information on control, see K-State publication MF-809, Alfalfa Insect Management 2017, at: http://www.bookstore.ksre.ksu.edu/pubs/MF809.pdf

Soybean Pests Update

–by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

Green cloverworms have moved into the pupal stage, for the most part, and thus have finished feeding on leaves.  There will probably be another generation of green cloverworms so any late planted soybeans may be at risk for defoliation again although it probably not enough to warrant an insecticide application.  Adult bean leaf beetles and stink bugs may also still be present in soybean fields and feeding on beans as long as they are still filling inside the pods, so monitoring should continue until pods are mature.

Mimosa Webworm

— by Dr. Raymond Cloyd

Now is the time of year when mimosa webworm (Homadaula anisocentra) larvae (=caterpillars) are feeding and creating their protective habitat on honeylocust (Gleditsia triacanthos) and mimosa (Albizia julibrissin) trees. The larvae (=caterpillars) are 1/2 inch in length when fully-grown, and rapidly move backward when disturbed (Figure 1).

Figure 1. Mimosa Webworm Caterpillars Feeding On Leaves (Raymond Cloyd)

Fig 1. Mimosa Webworm Caterpillars Feeding On Leaves (Raymond Cloyd)

 

The caterpillar webs leaves together on the ends of branches (Figure 2).

Figure 2. Mimosa Webworm Webbing On Branch End (Raymond Cloyd)

Fig 2. Mimosa Webworm Webbing on Branch End (Raymond Cloyd)

Webbing typically starts at the tops of trees and serves to protect caterpillars from natural enemies (parasitoids and predators) and insecticide spray applications. Heavily-infested trees are brown or scorched in appearance (Figure 3) as the caterpillars skeletonize the leaf tissue. Caterpillars eventually fall from trees on a silken strand before pupating. Mimosa webworm pupates in bark crevices or pupae will be glued to structures (e.g. building). In regards to controlling mimosa webworm infestations, it may be too late although initial damage may be minimal. Insecticides that may be used to suppress mimosa webworm populations, in which the caterpillars are exposed, include: acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel), spinosad (Conserve), carbaryl (Sevin), and several pyrethroid-based insecticides (e.g. bifenthrin and cyfluthrin). Read the label of each product to ensure that “webworms” are listed on the label. High-volume spray applications are essential in order to contact the caterpillars inside the protective webbing. If trees are already heavily-infested with webbing then it may be too late to apply an insecticide. If possible, selective pruning can quickly remove isolated or localized infestations of mimosa webworm.

Figure 3. Mimosa Webworm Feeding Damage (Raymond Cloyd)

Fig 3. Mimosa Webworm Feeding Damage (Raymond Cloyd)

 

Sorghum

–by Dr.  Jeff Whitworth and Dr. Holly Schwarting

Sorghum is in various stages of development around NC Kansas. The late planted, which seems to be just in the whorl stage- to soft dough, or even farther along. Corn earworms (often called sorghum headworms/soybean podworms etc., depending upon the crop infested) are causing significant infestations and therefore concern because of the highly visible whorl feeding and subsequent “ragged”-looking leaves as they expand from the whorl. This feeding probably will have no effect on yield, and by the time the damage is noticed the worms are mostly finished feeding anyway. Therefore, treatment is rarely justified. Feeding on the kernels however which is the marketable product is a different story. Sampling for head-feeding worms is really relatively easy. Just take a small white bucket, bend the head over into the bucket and vigorously shake it against the sides of the bucket which dislodges the larvae. Then count the worms and divide into the number of heads sampled.

Sorghum headworms_small

Rule of thumb: kernel-feeding larvae cause 5% loss/worm/head. Sorghum heads are most vulnerable from flowering to soft dough. These larvae are relatively susceptible to insecticides so efficacy is usually pretty good. However, these insecticides will reduce beneficial insect populations which can help later if any aphid populations develop.

Sorghum hedworm_single

Sorghum Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Chinch bugs are really common in sorghum fields throughout north central Kansas.  Their feeding will weaken stalks if dry conditions are prevalent.

Green lacewing eggs were present, indicating the presence of future beneficials to help with control of potential future aphid populations.

lacewing egg

chinch bug nymps2

Geraniums and Petunias Beware of the Tobacco Budworm

By Dr. Raymond Cloyd

Have you noticed that your geraniums and petunias are not blooming (flowering)? Well, the “critter” or culprit causing the problem may be the caterpillar or larval stage of the tobacco budworm (Heliothis virescens). Adults are pale-green to light-brown with the forewing marked with four light wavy bands (Figure 1).

Figure 1: Tobacco budworm adult
Figure 1: Tobacco budworm adult

The wingspan is approximately 38.0 mm. Adult females can lay between 500 and 1,000 eggs within 2 to 3 days. Caterpillars are 38.0 mm in length when full-grown and vary in color depending on the host plants fed upon. The caterpillars (larvae) may be black, pale brown, yellow, green, and/or red. They may also possess stripes that extend the length of the body (Figure 2).

Figure 2: Mature larva (caterpillar) of tobacco budworm
Figure 2: Mature larva (caterpillar) of tobacco budworm

Furthermore, caterpillars may have small hairs or setae on localized sections of the body. The caterpillars tunnel into buds (Figure 3)

Figure 3: Tobacco budworm larva (caterpillar) tunneling into petunia flower bud
Figure 3: Tobacco budworm larva (caterpillar) tunneling into petunia flower bud

and feed from inside or chew flower petals, which appear ragged (Figure 4).

Figure 4: Tobacco budworm larva (caterpillar) feeding on petals of petunia flower
Figure 4: Tobacco budworm larva (caterpillar) feeding on petals of petunia flower

Damage usually increases during the growing season. Furthermore, caterpillars feeding inside flower buds on developing ovaries will destroy flowers. Be on the look-out for black fecal deposits (“caterpillar poop”) (Figure 5)

Figure 5: Black fecal deposits ("caterpillar poop") associated with tobacco budworm larva (caterpillar) feeding
Figure 5: Black fecal deposits (“caterpillar poop”) associated with tobacco budworm larva (caterpillar) feeding

on the flower petals or on leaves below the flowers, which is a clear indication that the caterpillars are feeding. Tobacco budworm caterpillars will feed on a number of annual bedding plants besides geraniums and petunias, including: ageratum, chrysanthemum, nicotiana, snapdragon, and strawflower. Ivy geraniums may be less susceptible than other geranium types. The way to deal with tobacco budworm populations is to apply insecticides before the caterpillars tunnel into the buds using materials containing the following active ingredients: spinosad, cyfluthrin, permethrin, or bifenthrin. Be sure to thoroughly cover all plant parts as tobacco budworm caterpillars will also feed on plant leaves.

 

You can find more information on tobacco budworm feeding on petunia in the following article:

Davidson, N. A., M. G. Kinsey, L. E. Ehler, and G. W. Frankie. 1992. Tobacco budworm, pest of petunias, can be managed with Bt. California Agriculture 46 (July-August): 79.

Subscribe

Follow this blog

Get every new post delivered right to your inbox.