Brown Marmorated Stink Bug Provisional Guidelines for Pears
Scientific name: Halyomorpha halys
DESCRIPTION OF THE PEST
The brown marmorated stink bug (BMSB) is native to East Asia. In California, it was first found at a public storage facility in Riverside County and at a similar facility in Solano County in 2005. The California Department of Food and Agriculture declared it to be established in Los Angeles County (Pasadena) in 2006. Since then, it has been found in other California locations; however its precise distribution isn't known. Currently, confirmed infestations are limited to a few urban areas of several counties. As of September 2015, no established populations of brown marmorated stink bugs have been identified from farms.
The adult brown marmorated stink bug has a shield-shaped body similar to other stink bugs; it is about 5/8 inch long, and marbled (marmorated) brown. Females are slightly larger than males. Brown marmorated stink bug adults can be distinguished from other stink bugs of comparable size and color by the following characteristics:
Stink bugs have scent glands located on the back of the abdomen and the underside of the thorax. In the brown marmorated stink bug, these scent glands produce a cilantro-like smell when it is disturbed or killed.
Eggs are round to barrel shaped, white to pale green, and laid on the underside of leaves in clusters of 20-30; often clusters have 28 eggs. Nymphs shed their exoskeleton (molt) as they progress through five stages (nymphal instars) before becoming adults. Nymphs range in size from 0.1 inch (2.4 mm) for the first instar to just under 0.5 inch (12 mm) for the fifth instar.
The newly hatched nymph has an orange abdomen with dark brown plates and brown head and thorax. First instars remain clustered around the egg cases feeding from the egg before dispersing, sometimes remaining until they molt to the second instar. The newly-molted second instar has an almost black appearance and resembles a tick. Subsequent instars (third through fifth) have a marbled brown head and thorax and reddish brown, black, and white abdominal markings. They have distinct white bands on the antennae and legs. Like other stink bugs, fourth and fifth instar nymphs have visible wing pads. Newly molted adults may be white.
The number of brown marmorated stink bug generations per year depends on seasonal temperatures. First generation eggs are laid in mid-spring, but the specific timing is weather dependent. To calculate degree-days (DD) once the timing of egg laying has been identified, use a lower threshold of 62.6°F and an upper threshold of 91.4°F; 538 DD are needed for total development (egg to adult) plus 148 DD to egg-laying, for a total of 686 DD from egg to egg. Generations begin to overlap by July. The length of time in each stage also varies depending on seasonal temperatures. Generally, two full generations are expected, though in cooler parts of California there may be only one generation and in the warmest areas of the state there may be up to three.
There are limited field observations for brown marmorated stink bug development in California. In Sacramento, where first egg mass sightings were intensely monitored in 2014 and 2015, the first egg mass was found May 5 in 2014, but in 2015, (characterized by a very warm late winter and early spring) the first eggs were found April 14. Adults lay eggs over an extended period, so pinpointing egg-laying by the offspring of the overwintering generation is difficult. In Sacramento, the adults of this generation may be found in late June or early July, and they will start to lay eggs in early July.
Observations from other states show that brown marmorated stink bug, like many other stink bugs, generally migrates into orchards, vegetables, and certain field crops from overwintering sites and adjacent infested crops after they are harvested. However, while most stink bug adults overwinter in protected area under leaves and trash, in the crowns of plants, and in clumps of grass on the orchard floor, brown marmorated stink bug usually overwinters in sheltered areas such as buildings or under bark of large trees. Just before they seek shelter in late summer, they may aggregate in large numbers. If conditions are conducive, such as when diverse fruit crops are available through much of the season and larger trees with plentiful bark cracks are present, some brown marmorated stink bug adults could reproduce and overwinter in orchards.
For more information on identifying brown marmorated stink bug, see the UC ANR video: Brown marmorated stink bug: Identification and comparison to consperse stink bug
Damage from brown marmorated stink bug is indistinguishable from damage by other stink bugs. However, brown marmorated stink bug may reach very high numbers with multiple individuals present on a single fruit. Since one bug can feed on many fruit, losses can be severe. Adults and nymphs inject tissue-destroying enzymes as part of their feeding, then suck juices from the affected fruits. Initial damage may appear as oozing of sap. Damaged flesh under the skin turns hard and pithy. When feeding occurs on younger fruit, discoloration may form, followed by pockmarks or fruit distortion as the fruit expands. Any such feeding damage makes fruits and vegetables unmarketable. They can also feed on buds, flowering structures, leaves, stems, branches, and small tree trunks. Feeding on trunks and branches does not appear to harm mature plants, but the effect on the health of young trees is still being evaluated. Damage is generally greatest on late-maturing fruit when numbers are highest and the bugs become more concentrated, but even early season damage on some species, such as peaches and nectarines, can be severe.
It is unknown how damaging brown marmorated stink bug will be on agricultural crops in California.
The brown marmorated stink bug is a serious pest of many fruit and vegetable crops. In Mid-Atlantic States, the crops most affected are apple, pear, peach, nectarine, lima bean, snap pea, pepper, sweet corn, tomato, field corn, and soybean. Other identified crop hosts include raspberry, blueberry, grape, hazelnut, pecan, cucumber, and pole and bush bean. In Sacramento, extensive feeding and damage have been observed on pome fruits, peaches, nectarines, persimmons, and figs. Brown marmorated stink bug has seriously damaged commercial hazel nuts in Oregon. Their potential to damage almonds and pistachios in California is not yet known.
Ornamental tree and shrub species that have been found to host large numbers of brown marmorated stink bug in Sacramento include tree of heaven (Ailanthus altissima), fruiting varieties of Chinese pistache (Pistacia chinensis), waxleaf privet (Ligustrum japonicum), trident maple (Acer buergerianum), catalpa (Catalpa spp.), and white mulberry Morus alba). Feeding on ornamental tree hosts often coincides with fruit maturing, but tree of heaven may host large numbers throughout the growing season.
A list of over 170 host species, including those that attract the highest densities, can be found at www.StopBMSB.org. The list of host plants will likely increase as the pest spreads to new regions.
Brown marmorated stink bug is a new pest. Therefore insecticides will play a key role in management, at least until effective methods that can be used in an integrated control program are developed.
There are several generalist arthropod predators that feed on brown marmorated stink bug including assassin bugs, praying mantis, spiders, and specialized predatory wasps (Astata spp.), but they do not provide effective control in commercial crops. Although a number of endemic parasitoids do attack native stink bugs, they are generally unable to reproduce in brown marmorated stink bug eggs.Brown marmorated stink bug embryos apparently have an immune response that destroys the parasitoid embryos about two days after they are laid.
Organically Acceptable Methods
At this time, few guidelines exist for organic management of brown marmorated stink bug. Protectants such as kaolin clay can reduce fruit damage when thorough coverage is applied.
Monitoring and Treatment Decisions
Monitoring for brown marmorated stink bugs includes the use of traps, plant inspection, and beat sheet sampling.
Traps and Lures
Brown marmorated stink bug traps catch both adults and nymphs; however, the efficacy of different trap types and lures is still being researched. One of the most effective traps is a 4-foot tall pyramid trap, consisting of an inverted clear plastic container with an entry cone opening that is attached to a pyramid-shaped, corrugated plastic stand. Darker stand colors attract more brown marmorated stink bug than light colors, and black has been shown to catch the most. Traps with shorter stands are also available, as are double-cone hanging traps that are placed in trees. Some studies have shown that smaller traps secured to the branches of host tree species (not simply hanging by a wire) may catch substantial numbers of brown marmorated stink bugs.
Lure studies have shown that a combination of two compounds results in greater trap catches than either by itself. One scent is an aggregation pheromone, which is very similar to that of the harlequin bug, and the other is the "synergist" methyl decatrienoate (MDT). Some companies have the two compounds in separate lures, and in other cases they are combined into one lure. The lures attract the bugs from fairly short distances (within about 100 feet). It has been observed that even though the insects are attracted by the lures, many do not enter the traps, where they are captured, and instead remain on the surface of the traps or in the general vicinity of the traps. To ensure that stink bugs don't walk back out of the trap's entry hole, use an insecticide strip to kill them inside the trap; replace the strip according to manufacturer recommendations.
Trap captures are generally greatest in late summer, when brown marmorated stink bug seeks to aggregate before winter diapause and their numbers are at a seasonal peak. Early-season captures are enhanced by the MDT scent but nonetheless are often very low or non-existent when numbers are low to moderate. Treatment thresholds based on brown marmorated stink bugs found in traps have yet to be established for any crop. However, some East Coast studies have shown that a cumulative finding of 10 brown marmorated stink bugs in a trap may be an appropriate treatment threshold for apples and peaches; after each insecticide application, the count goes back to zero.
Plant Inspection and Beat Sampling
Because brown marmorated stink bug trapping can be inefficient, visual inspection of foliage (for adults, nymphs, spots of exudate (ooze), and egg masses) and beat sheet sampling (to dislodge bugs from the plant canopy) should also be done to determine if it is present in the orchard, especially if it has been found in the area. This monitoring will be especially important for early detection of possible infestations when brown marmorated stink bug is found in nearby urban areas. Inspect edge trees in the orchard as well as nearby host plants, especially tree of heaven when it is present. Beat host plant branches onto a beat sheet or tray. Beat sampling is much quicker than inspection. Sample in the early morning as adults may fly away during warmer times of the day. If eggs or young nymphs are found, an insecticide application targeting the more vulnerable nymphal stages might be warranted.
Because brown marmorated stink bug is still a regulated pest in California field insecticide studies have not been conducted, hence potential efficacy of registered products must be extrapolated from studies conducted elsewhere in the U.S. When using guidelines developed from other states, always check insecticide labels to make sure that a product is registered for use in California on the target crop before making any applications.
Brown marmorated stink bug has proven to be very disruptive of established IPM programs in areas where it occurs in abundance. During years with occurrence of large numbers, many mid-Atlantic fruit and vegetable growers make weekly insecticide applications for brown marmorated stink bug that includes alternate-row treatments on orchard crops, from late May through harvest using various broad-spectrum chemicals including pyrethroids, neonicotinoids, and carbamates. Some of these chemicals are used in combinations and premixtures. Recent research has shown that, in some cases, effective control may be obtained with only spraying of orchard edges. The frequency of applications in the mid-Atlantic is somewhat determined by the abundance of brown marmorated stink bug and frequency of rainfall events, as the insecticide residues may be washed off by rain. The potential for occurrence of large numbers that will require treatment in California is not known.
Some insecticides have been found to have greater efficacy against brown marmorated stink bug at different times of the season. It is likely that most insecticides that are effective for native stink bugs in California will also be effective for brown marmorated stink bug. In general, these products will be most effective when applied against younger-instar nymphs, and least effective against adults, and are also most effective when they directly contact the stink bugs. Residual efficacy is greatly diminished within a few days for stink bugs that enter the orchard after application, which is why weekly applications are used in mid-Atlantic states.
Chuck Ingels, UC Cooperative Extension Sacramento County
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