Japanese Beetles (Popillia japonica) are a destructive pest of turf, landscape, agriculture, and ornamental plants. They were introduced into the United States sometime in the early 1900s on a shipment of iris bulbs. They were first identified in a nursery near Riverton, New Jersey in 1916 during a routine inspection. They are also found in their native Japan, China, Russia, Portugal, and Canada. They have become an important pest as both larvae and adults destroy roots and defoliate plants. The Japanese beetle easily established in the U.S. after its introduction. As with a lot of introduced pest they were lacking in natural enemies and found an abundant food source and favorable climate. Efforts have been made to control these invasive pests. In 1918, the USDA and New Jersey authorities attempted to eradicate the infestation. But after only two years the populations were so well established the efforts were deemed unproductive and were stopped. The best strategy for eradication is early detection, isolation and the total elimination of populations. The annual cost of control in the U.S. exceeds $460 Million (Shetlar 2008).
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What are the implications of the introduction of Japanese beetles? And how can their spread across the United States be stopped in their tracks? This paper will be a thorough look into how Japanese beetles have spread across the U.S. and how to cope with this pesky pest.
Description of Japanese Beetles Life Cycle
Japanese beetles are polyphagous generalists and have a wide range of over 300 hosts. They are important pests of fruit, vegetables and field crops. Japanese beetles have one generation per year. A percent of the grubs may take two years to mature based on the soil conditions if they are cold and wet. The larvae are white colored grubs and are typically C Shaped around 1 inch in length. The third instar larvae overwinter in the soil below the frost line. The grubs develop in the soil feeding on the roots of plants. They can destroy lawns and turf grass. They are considered the most destructive pest of turf-grass in the United States. The adults are gregarious and collect together on a single plant. Single plants and trees may be completely defoliated. The adults are Â½ inch in length and are metallic green with bronze-colored elytra. The males are typically smaller in size than the females. The adults skeletonize the leaves of their hosts by eating the material between the veins. The veins are often left untouched after feeding and the leaves will crumple and die. They feed on the upper and outermost parts of the plants and work their way down the plant (Cook and Gray 2010).
Japanese beetles are found throughout the Midwest and eastern United States and are spreading west ward. The furthest west they are expected to reach on their own is central Nebraska because of the unfavorable climatic conditions. There are areas in Western states that are suitable for their survival if they hitchhike to the area. The movement of these pests is a major concern to horticulture and farmers. They have been introduced into California three times and successfully eradicated. Material such as nursery commodities, sod, soil, compost and manure from infected states are now prohibited without a PPQ inspection. The USDA closely monitors the movement of cargo planes into the unaffected areas. The beetles are known to fly onto the cargo plane when the doors are open during times of adult beetle flight (Hamilton et al. 2007).
Airports are potential vectors for Japanese beetle infestation. A State Plant Health Director which is an APHIS employee arranges a monitoring survey to determine the risk status of an airport. Inspectors survey the airport to determine the potential risk. Monitoring surveys will determine the threat of entry into the aircraft and the population level in surrounding areas. The Indianapolis Airport is one of many airports where Japanese beetles pose a threat. Traps around the airport over a 4 year period showed that the relative distribution of adult beetles along the trap line were stable and at the same level in the same areas. Conclusions were drawn that the environment around the airport has considerable influence on the distribution of beetles and potential threat of a hijacker flying on board. The soil type, land use, location of host and nonhost plants, soil moisture all effected the movement of the Japanese beetles. A change in the environment such as land use and irrigation could affect the Japanese beetle distribution and be a viable practice to decrease the Japanese beetles' opportunities to fly onto open airplanes (Hamilton et al. 2007). By manipulating the land around the airport the risk could be minimized.
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In 1917 the former U.S. Bureau of Entomology established the Japanese Beetle Laboratory in 1917. They studied the biology of the pest in its new environment and worked on developing methods for control (Potter and Held 2002). They studied the pest-host interaction attempting to gain an understanding of this invasive pest. Entomologists realized this introduction had the potential of becoming a devastating pest that would lead to high economic costs.
In 1998, the National Plant Board initiated the first version of the U.S. Domestic Japanese Beetle Harmonization Plan. This established a plan for the movement of commodities that host Japanese beetles such as nursery stock and other regulated commodities. This program has two objectives to establish a framework that encourages states to assess the Japanese beetle risk and infestations status. The second objective is to provide a more uniform adoption and implementation of pest risk improvement measure to reduce the risk of pest introduction to receiving states. Nursery stock will requires a phytosanitary certificate for moving to states that consider Japanese beetle a quarantine pest (National Plant Board 2011). Movement is restricted from quarantined states, all but Florida, Mississippi, and Louisiana in the east are restricted. Infestations west of the Mississippi River are eradicated before they become established, although partial infestation occurs in Arkansas, Iowa, Kansas, Minnesota, Missouri, and Oklahoma.
Areas that are at risk for introduction have implemented protocols to eradicate this pest if they are introduced. If the Japanese beetle becomes established in Oregon and generally disperses throughout the state, the economic impact to all crops, commodities, and other related businesses could be over $34 million (Hamilton et al. 2007). The absence of natural enemies has allowed the Jap beetles to establish and spread in areas with little predator control. The indigenous host plants that Japanese beetles use as foods source are highly susceptible due to the lack of coevolutionary history with the beetle leaving the plants defenseless.
Japanese beetles are classified as an A1 quarantine organism for EPPO and of quarantine significance for CPPC, JUNAC, and OIRSA. They are at low risk of establishing in the Mediterranean area, and the risk is also low in the UK, Ireland and continental Europe north of 53N, because of the naturally cool summers. The area of concern is between latitudes 43N and 53N east to longitude 30E. If they are introduced and established they could cause massive damage and have significant economic loss. The EPPO makes a suggestion that countries prohibit the importation of plants with roots from countries where P. Japonica is established. If material is imported it should be planted in inorganic growing medium or in treated medium and kept under conditions which prevent infestation (Potter and Held 2002). The removal of soil from the roots of nursery plants will remove the larvae, in some cases the soil should be treated. The Japanese beetle was established in Terceira Island where in 1970 it escaped from a U.S. air base (National Plant Board 2011).
Japanese beetles release an aggregation pheromone and often are found in mating clusters. Invasive pests can benefit native populations through the plant stress-mediated interactions. Grapes are among their preferred hosts. This is an interesting interaction between an invasive species benefiting a native species. The Japanese beetle facilitates the green June bug feeding on grapes by biting through the skin providing access to the GJB and by eliciting yeast-mediated fermentation volatiles that the GJB uses in host-finding and aggregation. The GJB are usually unable to break through the tough skin of grapes so they benefit from the Japanese beetle feeding. This allows the GJB to expand its range into the fruit-growing region. Green June bugs were able to feed on grape plants before but the Japanese beetle injury leads to an additive increase in feeding and aggregation by breaking apart the fruit and attracting the GJB to the plants. In this case Japanese beetles have elevated the economic impact of an indigenous species (Hammonds et al. 2009). If these beetles are introduced and established into California this could potentially threaten the grape industry.
Damage and Management of Japanese Beetles:
Japanese beetles have favored hosts that they prefer to feed on but will feed successfully on a list of non-preferred hosts. The preferred hosts successfully attract the beetle to feed. Since they attract other beetles to food sources, killing beetles or hand picking them off plants will reduce the populations. Some commercial traps bated with pheromones will also attract them. Grubs have trouble surviving in dry soils, so irrigation should not be used if an infestation is suspected. Bacillus papillae, a bacterial milky spore disease can kill the buried grubs. The bacteria can be applied to the soil and the spores will remain in the soil to infect further inhabitants (Shetlar 2008).
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The insect-plant system is a complex interaction that understanding will benefit management strategies. Japanese beetles are generalists that feed on over 300 species making them an important pest of horticultural crops. They are attracted to hosts by green leaf odors and color instead of specific host stimuli. These generalists avoid nonhost plants because they sense deterrents in these plants such as cucurbitacins, a bitter triterpenes characteristic of cucurbits (Potter and Held 2002).
Although, corn and soybeans plants are not a preferred host of the Japanese beetle, they can do considerable damage defoliating soybeans and feeding on silks of corn plants which can reduce the pollination and kernel set. Both the grubs and adults can cause injury in corn. The grubs are able to feed on the root hairs of the plant which interferes with the plant taking up water and nutrients. If fields are heavily infested they can experience reduced plant stands. The adults beetle feed on the silks and this interferes with pollination. In soybean fields, they can also cause damage in both the larvae and adult stage. The grubs also feed on the root hairs of the soybean plants, this usually and economic important issue. The adults can cause extensive damage to the soybean plants, if this happens during the reproductive stages during the plant life a loss in yield will occur. They will feed on the flowers and defoliate the leaves. Management can be difficult. Adults are very mobile and can quickly move from fields. Fields should be scouted to determine the percent defoliation and to correctly identify the species. If the standard economic thresholds are met for corn or soybeans the fields should be sprayed with insecticide (Cook and Gray 2010).
The larvae have limited mobility so the oviposition site is very important for survival of the offspring. They have a strong preference to oviposit in grass the chemical cues stimulate females to lay eggs in the soil (Szendrei and Issacs 2005). Japanese beetles have an interesting mating behavior. The egg load and body size may influence their mating frequency. They have a promiscuous mating system in which both males and females mate repeatedly during their lives during this type the females moves to the soil to lay her eggs. The males are attracted to the virgin females by sex pheromones released (Tigreros and Switzer 2010). They seek out non-virgin females on food plants where they tend to aggregate. There is a last male advantage for fertilization in sperm competition. The males will mount unpaired females or try to remove the male from the paired female. Males may stay on the female for a couple hours "guarding" the female. Males will choose larger females over smaller females and guard these longer. This could be because larger females have more eggs and may oviposit more frequently (Switzer et al. 2008).
Management systems are multifaceted and can be complicated when trying to treat both the grub and adult stage. They both damage plants through different modes of feeding. The adults are mobile and move from place to place while the grubs are restricted to the area where the female laid her egg. They need to be laid by a suitable host for feeding if they are to survive.
Cultural controls can help decrease the larval populations in grasses. Avoiding irrigation during peak beetle flights this can make it difficult for the beetles to oviposit. One of the interesting discoveries was concerning geraniums. Beetles that feed on petals of geraniums roll over on their backs and remain paralyzed for 24 hours. They will typically recover but under field conditions are often preyed on by predators. Some type of substance in these plants paralyzes the beetle. The plants do not deter feeding and could potentially be used as a control agent for Japanese beetles if the volatile could be identified (Flores 2010).
The Japanese beetle problem should be treated using an IPM strategy to fight the infestation. A couple of management tips to follow are to avoid irrigation in areas where grubs are feeding and to avoid planting plants that are preferred hosts of Japanese beetles. Spot treat areas with insecticide if infestation is heavy, treat lawn with pesticides when the soil is wet for better absorption. Being aware of the life cycle of this pest and ways to manage them can help decrease expanding populations. Infestations are usually a threat in areas where there is a history of feeding, so scout and be aware of the potential threat.
Since the accidental introduction of the Japanese beetle into the United States they have slowly spread throughout the country threatening indigenous plants and ecosystems. The Japanese beetles are here to stay. They are voracious generalists that aggregate and can quickly defoliate plants and trees. Their grubs can destroy turf grass leaving irritating bald areas across your lawn. Comprehensive strategies restricting the movement of these mobile pests are in place and should be stringently followed. Stopping the spread of these beetles is very important for areas in the West such as Oregon and California where preferred host plants would be ravaged by their feeding. The combination of their mobility and reproductive capabilities makes Japanese beetles an invasive pest that will need to be closely monitored and quarantined in the present and future.
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