MPI is on high alert to keep out one nasty, stinky insect.
Preparing for emerging pests and diseases that could affect New Zealand's environment and economy is a key role for the Ministry for Primary Industries. The Ministry has been keeping an eye on the brown marmorated stink bug ( Halyomorpha halys or BMSB) for a number of years now and has stepped up its efforts to keep this pest out of New Zealand - or detect it early should it get here. This is in response to the insect emerging as a serious horticultural pest in the United States.
BMSB is native to Asia and has aggressively invaded the United States and has now been found in Canada, Switzerland, Germany, Italy and France. At present it is regarded by the New Zealand horticulture industry as one of the top six pests of concern.
BMSB feeds on more than 300 hosts, primarily fruit trees and woody ornamentals but also field crops. Almost any crop can be at risk, including: citrus; pipfruit; stonefruit; berries and grapes; asparagus; soybeans and maize; honeysuckle; maple; butterfly bush; cypress, hibiscus; and roses. In its native habitat of East Asia, BMSB is a pest of fruit trees and soybeans. It feeds by sucking plant juices. Adults generally feed on mature and immature fruit, while nymphs feed on leaves and stems as well as fruit. It severely disfigures fruit and renders it unmarketable, which results in control costs and production losses. BMSB damage to woody ornamentals and forest trees has been reported as cosmetic only. In the US, BMSB has been primarily reported as a household nuisance and ornamental pest, but it has also caused economic losses in tree fruit and soybeans.
In a study of populations at farms in New Jersey and Pennsylvania, BMSB caused about 25 percent premature fruit drop. Its piercing/sucking action causes necrotic spots on fruit and leaf surfaces that may then be compounded by secondary infection and scarring as the fruit matures. In particular, apples are often pitted and discoloured, and peaches frequently display a distinctive distortion called ‘catfacing'.
Adults are about 15mm long with a distinctive brown shieldshape. The underside is white to tan and the legs are brown with white banding. Eggs are light green, barrel-shaped and found in clusters laid on the underside of leaves.Young nymph stages are yellowish brown, mottled with black and red. Older nymphs become darker and develop the banding pattern on the legs, antennae and sides of the abdomen.
BMSB has only one generation per year in the northern states of the US. However, in the southernmost part of its native range in southern China up to five generations occur each year. BMSB overwinters in the adult stage, mating in spring about two weeks after emerging from the resting phase. Soon the females begin laying egg masses at about weekly intervals on the underside of leaves and occasionally on stems and fruit.
Each female lays up to 400 eggs in her lifetime and the first-instar nymphs emerge after four to five days. There are five nymphal stages, each lasting about a week depending on temperature, and the adults become sexually mature two weeks after the final moult. In Pennsylvania, where females have been seen laying eggs from June to September, all stages are often seen simultaneously on the same host plant. The nymphs are solitary feeders but occasionally aggregate between overlapping leaves or leaf folds. Adults are very active and drop from plants or fly when disturbed. The optimal temperature for BMSB development is 25ºC, while nymphs will not develop below 15ºC and eggs below 12ºC.
Aggregations of adult BMSB overwintering in buildings and houses can be a nuisance, as when disturbed or crushed they emit a characteristic, unpleasant, long-lasting odour (although this does not pose any health threat).
BMSB is a strong flier and highly mobile pest. Once established, it can spread quickly over long distances through movement of host plants, goods and vehicles.
Establishment of BMSB depends on favourable temperatures for survival at the time of introduction of an egg mass, or males and females, or even a single gravid female.
Chemical treatments in the USA so far are limited, but there has been good progress in research into trap-and-kill techniques. Contact with these researchers is enabling MPI to keep abreast of the best available research.
BMSB is thought to have invaded the US in shipping containers. Because the adults hide in cracks and crevices during winter months, they can spread in all kinds of cargo, including personal effects and housewares. Risk countries of origin include the US, China, Japan and Korea. BMSB is also associated with imported dunnage, wooden boxes or containers.
Identification of BMSB by molecular and morphological means is available in New Zealand and any incursions are likely to be detected by the Ministry for Primary Industries' targeted High Risk Site Surveillance (HRSS) programme. Good phytosanitary measures are the best way to prevent introductions, and early detection through surveillance is the key to eradication before the pest can become established.
MPI is currently trialling 50 traps in high risk areas to determine the feasibility of integrating pheromone lures for BMSB into its existing trapping programmes. Border and transitional facilities have also been put on alert for BMSB. Strict biosecurity requirements on imports, checks at the border, surveillance programmes, and capability to respond to a pest incursion, all work together to help prevent known pests such as the brown marmorated stink bug establishing in New Zealand. Although we can never have a 100 percent guarantee or zero risk, this approach has kept New Zealand free of many of the worlds' worst pest problems.