Brown marmorated stink bug

What do growers, chocolate lovers, car manufacturers, and homeowners have in common? Hostility to brown marmorated stink bugs. By Anna Mouton.

The brown marmorated stink bug — Halyomorpha halys — is a pentatomid bug. Familiar pentatomids include antestia — Antestiopsis thunbergii — and green stink bugs — Nezara viridula. All these bugs are in the order Hemiptera. Hemipterans have piercing-sucking mouthparts. Most of them pierce and suck plants but some are predators.

Halyomorpha halys has gained notoriety both as an agricultural pest and as a serious nuisance to businesses and homeowners.

Why do brown marmorated stink bugs matter?

Halyomorpha halys has been reported from more than a hundred host plants, including pome and stone fruit, citrus, grapevines, blueberries, cereals, soya, vegetables, and cannabis. Both mature and immature stages prefer to feed on developing and mature fruits and seeds.

Feeding damage causes brown spots and dimples on fruit. Apples may have corky areas in the flesh. Feeding early in the season can cause fruit to drop. Early damage can also lead to deformation — known as cat facing — as fruit develop. Preharvest damage sometimes manifests during cold storage.

Invasive brown marmorated stink bug resulted in losses of USD 37 million to apple production in the mid-Atlantic region in 2010. It is reported that some stone-fruit growers lost more than 90% of their crop that year.

Some researchers have claimed that Halyomorpha halys in wine grapes can result in tainted wine. Even worse, these bugs cause severe damage to hazelnut production, thereby potentially threatening the global Nutella supply.

Brown marmorated stink bugs are more than just agricultural pests. The adults aggregate during autumn in sheltered spots. They overwinter in groups of hundreds or even thousands in houses and have been found in cardboard boxes, in shipping containers, between boards, in folded tarpaulins, and even in vehicles and machinery. As a result, cars manufactured in affected areas of the United States must be fumigated or heat-treated before entering the ports of some countries.

Halyomorpha halys does not occur in South Africa. All evidence suggests that it would thrive if introduced here, possibly becoming a serious pest of pome and stone fruit, as well as many other crops. Phytosanitary measures required by our trading partners could also affect other industries that ship products abroad.

How do I recognise these bugs?

Pentatomid bugs are known as shield bugs because their body is shield-shaped. Brown marmorated stink bugs are brown and marmorated — which means mottled or marbled. Adults are 12–17 millimetres long and 7–10 millimetres across their shoulders.

Halyomorpha halys adults have light bands on each antenna and a single light band on each leg. They have alternating light and dark markings on the abdominal margin. Their shoulders are smooth. Juveniles are harder to identify as not all stages have these characteristics.

How do these bugs make more bugs?

Females lay clusters of 20–30 eggs on the undersides of leaves. A single female can produce more than 400 eggs during her lifetime. Black-and-red hatchlings emerge after 3–6 days. They remain with the eggshells until their first moult after a further 3–5 days. Larvae then walk off to begin feeding on host plants.

Halyomorpha halys has five juvenile stages. A laboratory study showed that each of the first four stages takes about a week to complete at 25 °C. The fifth stage takes about two weeks. Development is temperature-dependent and stops below 11–14 °C.

The bugs complete 1–2 generations per year throughout most of their range. Overwintering adults become active in spring. Females will feed for about 1–2 weeks after overwintering before they start reproducing.

Where did it come from?

Brown marmorated stink bugs are originally from China, Japan, Korea, and Taiwan. They were discovered in the United States in the 1990s but were initially misidentified. The bugs have subsequently been reported from most states, as well as from Canada. Chile is the only other country in the Americas where brown marmorated stink bugs are present.

In Europe, the bugs seem to have first settled in Zurich in 2004. Brown marmorated stink bugs have been reported from several European countries, including France, Germany, Italy, Portugal, Spain, Greece, and the United Kingdom.

The global spread of Halyomorpha halys is associated with overwintering adults in cargo. Although these bugs could travel on plant material, this appears to be a less important route of transmission. Adults can disperse once established in an area — they have been shown to fly an average of two kilometres per day in laboratory trials.

Brown marmorated stink bugs have not been found in either South Africa or any other part of Africa. Their attempts to enter Australia have thus far met with eradication.

Control of brown marmorated stink bug

In the United States control of Halyomorpha halys in tree fruit has mostly relied on pesticides. Fruit are vulnerable to damage at all developmental stages and multiple applications throughout the season are necessary. The need to protect fruit up to harvest must be balanced with limitations on residues. Overwintering adult bugs are more sensitive to pesticides than bugs that develop later in the season.

In some cases, pesticide use for Halyomorpha halys has led to the destruction of beneficial insects and the resurgence of other pest species, such as European red mites and woolly apple aphids.

Predators and parasitoids are believed to be important in controlling brown marmorated stink bugs in their native countries. Their effect on invasive bug populations has been variable. Nonetheless, biocontrol is likely to play an increasingly important role as pesticides come under ever greater pressure.

Monitoring relies on blacklight traps. Aggregation pheromones for Halyomorpha halys are available but only attract adults later in the season when they are preparing to overwinter.