Japanese Beetle Adults Continue to Emerge Across Missouri

Published: July 17, 2013

During the past two to three weeks Japanese beetle adults have been emerging in many Missouri counties. Although beetle numbers remain high in some regions of Missouri, in general numbers emerging statewide in 2013 are reduced from numbers observed in years 2011 and 2012. Although the exact cause for reduced Japanese beetle adult numbers remains unknown, the drought of 2012 may be a factor. Female adult Japanese beetles generally lay about 40 to 60 eggs in groups of 1 to 8 eggs during each egg laying event. Typically the female will feed prior to each egg laying session. After feeding, females will fly to the soil surface close to their feeding site, burrow 2-4 inches into the soil, and deposit eggs. Researchers have speculated that very dry soils may inhibit the ability of the female beetles to efficiently complete egg laying activities. In contrast, lighter soils or soils with elevated sand content may be more optimal egg laying sites and often support heavier beetle populations. Another factor that has been suggested is a shorter survival time of Japanese beetle adults when exposed to severe drought conditions. Hot dry conditions reduce the quanity and quality of many host plants resulting in increased beetle completion for limited resources. Similarly, much of the growth of the three white grub Japanese beetle stages takes place during summer into fall following egg hatch. If drought conditions exist during this time, survivorship of these grub stages also may be decreased. As in most biological systems, numerous factors interact to regulate insect populations. The importance of drought conditions in regulating populations of Japanese beetle adults and grubs remain to be determined.

Beetles often gather and feed high (often in full sunlight) on host plants which exude strong odors. Several tree species such as linden, many flowering shrubs, roses, and mature fruit are all favored hosts of this pest. In the United States the Japanese beetle is known to feed on over 400 plant species. Some soybean and corn fields have been sprayed during the past three weeks for this pest. Due to late planting of corn fields in several areas of the state, silks and to a lesser extent tassels have not been available as feeding sites. If beetles emerge into corn fields prior to silk emergence, adult beetles will often feed on corn leaves. Unless infestations are extremely high or silks production will occur within the next few days, this minor defoliation of corn leaves is generally considered non-economic. In contrast, Japanese beetle adult feeding on emerging and recently emerged green corn silks can reduced pollination and subsequent production of kernels. In field corn, an insecticidal treatment is justified if during the silking period an average of 3 or more beetles are present per ear tip, silks have been clipped to ½ inch or less in length from the ear tip, and pollination is less than 50% complete. Beetles often move as a group from ear to ear as they feed. It is common for some ears to exhibit major feeding damage whereas other nearby ears may not be damaged by Japanese beetle adults. If beetle infestations are intense, then most ears in an area will exhibit feeding damage. It is common to find 25 to 30 beetles feeding on silks of individual ears when pest infestations are high.

In soybean, feeding damage of adult Japanese beetle is often observed on the tallest soybean plants as a lace-like pattern of defoliation which avoids leaf veins. Foliage feeding on soybean may exceed economic threshold levels, especially on late planted or double-crop soybean. The grub stage of this pest will feed on plant roots of both corn and soybean with most feeding occurring after egg hatch into fall. Damage to plant root hairs may result in poor uptake of water and nutrients or be more severe and cause reduced stands through plant mortality. Limited information is available concerning the impact of root feeding by Japanese beetle grubs under summer and fall field conditions. Cool soil temperatures during spring of 2013 slowed grub development and pupation resulting in later than normal emergence of adult beetles. In the past two to three weeks foliar damage to soybean (greater than 20% defoliation) has forced the application of insecticides on some Missouri soybean fields in order to control damage from this pest. For soybean, an insecticide treatment is justified if foliage feeding exceeds 20% - 30% prior to bloom and 10% - 20% from bloom through pod fill. Use the lower threshold numbers if soybean plants are under drought stress. Numerous insecticides are labeled for control of Japanese beetle adults on corn and soybean crops.

Historically, the Japanese beetle was first found in the United States in Riverton, New Jersey in 1916, following its accidental introduction from its native country of Japan. It is thought that grubs of this pest were introduced in pots of exotic iris plants imported into the US prior to the initiation of federal plant and animal inspections in 1918. In Missouri, infestations of Japanese beetles were first found in the southern portion of the City of St. Louis in 1934. A Missouri Department of Agriculture bulletin list 51 different tree, shrub, vegetable, and field crop species being damaged by Japanese beetles in St. Louis by the summer of 1936. For many years the Japanese beetle infestation stayed in the St. Louis area although by the early 1960’s infestations were reported in the urban centers of Kansas City, Columbia, and Springfield. These urban infestations were initially associated with golf courses and plant nurseries where grubs of this pest were again introduced in soil and plants imported from states with earlier Japanese beetle infestations. Populations of this pest remained mainly in these urban area until the late 1990’s when this pest began spreading mainly west and south into more rural areas of the state. The Japanese beetle in Missouri is still in a colonization stage of population growth with continued dispersal in most counties of the state. At present, most rural areas of Missouri will experience increasing populations of this pest for the next 7 -10 years and maybe beyond. Beneficial biological pathogens and agents will eventually slow these expanding populations, resulting in annual population fluctuations at levels below peak populations experienced in earlier years.

Japanese beetle adults are approximately 1/2–inch in length, metallic green in color with bronze or copper colored wing covers. An excellent diagnostic characteristic for the adult of this insect is the presence of twelve white tufts of hair or bristles located around the edge of the shell (five running down each side and two located at the very back end). Without magnification, these structures are seen as white dots. Japanese beetles can be confused with adult green June beetle, but are smaller in size. Adult beetles typically begin emerging from the soil in early June, reach peak numbers in late June into early July and then diminish during late July into August. Adults emerge, mate and feed for approximately 45 days with some individual beetles living for up to 60 days. During this time each beetle female typically lays 40 to 60 eggs in groups of 1 to 8 into the soil with larvae emerging in about 2 weeks. Larvae will feed on plant roots and decaying material and grow through 3 larval instars (worm or grub stages) before overwintering in the soil. Following increases in soil temperature in spring, larvae quickly finish development, pupate, and usually begin emerging as beetles in early June in most years. Peak emergence in Missouri generally occurs during the first two weeks of July in most years. Wayne Bailey 573 864-9905 (cell)

Potato Leafhopper in Alfalfa. Potato leafhopper adults are greenish-yellow in color, wedge shaped and about 1/8-inch in length. Adult leafhoppers are very mobile and quickly move sideways, jump, or fly when disturbed. This is a native insect which migrates into Missouri each spring from more southern states and Mexico. The potato leafhopper is often transported into the state by early spring storms, especially those that contain hail. Migrating leafhoppers are thought to actively fly into storm fronts and be carried great distances by low level winds (jets) which approach 100 mph in speed. After a storm passes, high numbers of leafhoppers often can be found in the trail of the storms. In Missouri, the potato leafhopper adults generally arrive in early May of each year, but may also arrive with storms occurring in June and July. The arriving adults typically feed initially on several tree species before moving to alfalfa to feed and reproduce. Two to three generations of potato leafhopper are often produced with economic damage generally occurring on alfalfa following removal of first and possible second harvests.

Damage is caused when both adult and nymphal (immature) leafhoppers use their piercing-sucking mouthparts to penetrate alfalfa leaflets and stems. They remove plant juices and often cause yellowing “hopperburn” of established plants, stunted plant growth, and sometimes mortality of seedling alfalfa. Both forage quality and quantity are reduced by this alfalfa pest. Potato leafhoppers typically arrive in Missouri about May 5th each year, although their arrival in Missouri was delayed in 2013 with peak arrival occurring around the last week of June. Populations of this pest have exceeded the threshold level in many central Missouri fields during the past two weeks. Many fields were harvested to reduce pest numbers with others receiving insecticide applications. Fields most at risk are fields seeded to alfalfa during spring 2013, although all ages of plants can be severely affected by potato leafhoppers. Scouting is best accomplished using a 15-inch diameter sweep net. Take 10 pendulum sweeps at five random locations in the field. If the average number of potato leafhopper adult + nymphs per sweep reach or exceed the threshold numbers listed below, treatment is justified. Adults PLH have wings with nymphs similar in appearance, but without fully developed wings. The economic threshold for potato leafhopper in alfalfa depends on the height of the alfalfa and whether the alfalfa is a potato leafhopper resistant variety or a traditional alfalfa variety. Second and third cutting alfalfa crops are most at risk. Leafhoppers often cause severe plant loss to newly seeded alfalfa stands so monitor these fields often to determine potato leafhopper numbers and/or the presence of “hopperburn”. Traditional alfalfa varieties are more susceptible to damage from PLH adults and nymphs than newer PLH resistant varieties. See economic threshold table.

Insecticides labeled for control of potato leafhoppers in alfalfa include the following: