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Japanese Beetle News

Current information for homeowners and agricultural producers

Japanese Beetle Look Alikes


For pictures, go to this Minnesota Extension Factsheet
PLEASE NOTE: Control recommendations for Illinois may vary than those given for Minnesota.

ANNUAL WHITE GRUBS

Annual white grubs, the larvae of the southern masked chafer (Cyclocephala lurida) pass through one generation each year. The adult beetles tend to flit about at dusk during the early summer. Adult southern masked chafers do not feed, and seemingly have one purpose – to generate progeny (Masked Chafers HYG 2505-91, Ohio State University). The eggs, resulting from this "progeny fervor," are deposited in the soil and hatch within the span of a couple weeks. The larvae or grubs feed on roots and organic matter until fall when they migrate down in the soil profile. Spring temperatures draw the grubs back up into more shallow regions of the soil profile where they feed until about mid-late May. They pupate, at that time, resulting in another batch of southern masked chafer adults. Since planting in our area historically did not begin until May and annual white grubs pupated soon after, specialists typically termed annual white grubs "insignificant" to corn. However, our shift toward late March/early April planting has seemingly created a niche for this pest that once synchronized poorly with our growing season.

TRUE WHITE GRUBS

The term "true white grub" actually refers to a genus of grub-producing beetles rather than a distinct species. True white grubs are the immature stage of what many term May/June Beetles (genus Phyllophaga). Species belonging to this genus have a three year lifecycle. Adult beetles also appear in the spring, depositing eggs 1-8 inches deep in the soil. Those eggs hatch in a few weeks - later resulting in the small, cream colored, C-shaped larvae that we commonly refer to as "grubs." The individual grub molts once during that first growing season and then migrates deep into the soil profile (much like the annual grub). The following year, spring temperatures draw the grub back into more shallow regions of the soil profile initiating a second season of root feeding that tends to be the most destructive of the three feeding years. Fall again drives those grubs down, spring again draws them up, and the grubs feed into the late summer of the third growing season. They then pupate and later emerge as adults that begin the process anew the following spring. The extended nature of the Phyllophaga grub stage has typically cause entomologists to deem Phyllophaga species the more significant stand threat in central Illinois. However, we again mention that times have changed and that May/June Beetle grubs likely face stiff competition for the title of "most significant grub species."

FALSE JAPANESE BEETLE REMINDER

Local Master Gardeners and some area Extension educators noticed the first few Japanese beetles in our area, but they have also noticed a Japanese beetle look-a-like. The insect is known as the False Japanese Beetle and has been observed in area fields and yards. About one-half inch long and brown in color, False Japanese Beetles are a very common pest of roses in Mason and Tazewell Counties. They usually hide under the flower. As they hide, they feed on the petals devouring them and are often accompanied by about 2-3 identical feeding companions. Most homeowners notice these insects clinging to the plant only after the petals have been stripped away. The False Japanese Beetle becomes active in May (slightly early for the Japanese Beetle during most growing seasons) and remains in our area up to/slightly after the time of corn silk emergence.

The name, particularly the term "false," describes the False Japanese Beetle to a "T". This species is a convincing copy of the true Japanese Beetle. The only real differences between the two are tufts of hair that line the sides and back of the abdomen. In the true Japanese Beetle, these small, stubby "tufts" resemble a series of distinct white dots. However, the False Japanese Beetle has much longer scraggly masses of white hair around the posterior of the abdomen. In other words, it lacks these distinct white dots. Needless to say, the difference is subtle – but a trained eye can detect that feature and use it to distinguish between the genuine article and this convincing forgery. The wing covers of the "False" version are also rather dull while the wing covers of the "true" version are shiny/metallic bronze.

Adult False Japanese Beetles lay their eggs in sandy soil. The larva is a "C-shaped" white grub that feeds upon the roots of vegetation much like the larva of the Japanese Beetle.

So why mention them? People hate Japanese Beetles and get "trigger happy" when using insecticide against them. Individuals may panic and decide to start spraying for what is typically a "non-pest." While the False Japanese Beetle can play havoc with rose petals, it has not historically caused much damage in cornfields/other crops. Its identification in a field may allow producers to breathe a little easier, and its presence reiterates the importance of correct identification which can sometimes allow the grower or gardener to save a few dollars.

On a related note, some area growers and gardeners are noticing False Japanese Beetles, but they may soon see the "real deal." The first few "true" Japanese Beetles will probably make a noticeable central Illinois appearance by early to mid-June (we are almost there) as opposed to mid to late-June. The "crest" of the seasonal wave (i.e. the really rough populations that tend to strip away foliage) may appear in central Illinois about mid to late-June (again a couple/few weeks early). Populations will probably drop off by about mid-July, but the pest will still be observed in fields and yards well into August.

GREEN JUNE BEETLES

Fortune telling is a dangerous practice to get into when it comes to agriculture. Will it be a dry year? What type of yield will we have? Will prices go up? If one tries to answer any of these questions, he or she is more likely to be embarrassed than vindicated. However, when it comes to insects, a little bit more success may be dealt when one peers into the future. For instance, one can say with much certainty that within a little over two months, calls will start to come into the Extension office regarding the Green June Beetle.

Green June Beetles are usually regarded as a turf insect, but every now and then, the larval stage of this insect injures corn and sorghum.

At the time of this article, most Green June Beetles are overwintering as grub-like larvae several inches deep in the soil. With the onset of warmer weather, the grubs will migrate upward in the soil profile and begin to feed upon root tissue. If the unfortunate roots happen to be those corn or sorghum, grub damage, patchy wilting of young plants, will begin to appear in those fields.

The adults usually result in the calls made to the Extension office each year because homeowners note large numbers of the metallic, green beetles buzzing loudly around the yard. In most cases, those adults "buzz" around so fast and those adults are similar enough in size that they are misidentified as "hundreds of bumblebees" invading an area. The adults are about an inch long.

Are they dangerous to those observing? The simple answer is not really. However, venturing into the area does put one at risk of being hit by these beetles, which are in a fevered race to mate and lay eggs. As a matter of fact, one will note that these beetles suddenly appear from beneath the ground during sunny weather and then "dive bomb" back to the soil surface several times as they attempt to lay pearly white eggs in underground chambers. The adults cause minor feeding damage to some plant foliage.

For the producer, identifying this grub is a lot easier than identifying other grub larvae. With many other larvae, those scouting must closely examine the posterior underside of the grub to note the arrangement of small hairs. Green June Beetle grubs are easily distinguished from others because they crawl on their backs. Their six legs are much too short for these grubs to use effectively, and they, therefore, use hairs located on their back to provide traction for crawling. Often this crawling action will be noticed from May to July as the grubs come to the surface in theevening in search of food. By late June to early July, the two-inch long grubs pupate within the ground and emerge about two week later as the adult beetle stage.

Green June Beetles complete their lifecycle in one year, and as is the case with most larvae, they can not be treated for after damage is observed. During spring tillage or scouting tours, the producer should note the presence of any of these gray colored larvae, the population of these larvae, and proceed accordingly.



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