How to identify and control the brown marmorated stink bug
Stink bugs are common to almost every part of the world, and are members of the arthropoda phylum. To date there are around 40,000 species known to man, of which over 1,000 species live in Central Europe. Although each species is distinct they all share one common feature: a proboscis. From the egg stage, these bugs complete 5 nymphal instars before reaching adulthood.
The Brown Marmorated Stink Bug
Native to East Asia, the brown marmorated stink bug has become a well-established pest in recent years. Brought to Europe through trade and tourism, it was first sighted in Central Europe in Zurich in 2004. In the initial years these bugs were most commonly spotted in late summer or autumn, during their search for a winter habitat on sun-exposed house walls. Over time, they have spread their range throughout Central Europe and the population is now rising sharply. As a result of this increased prevalence, the BMSB, to use its common abbreviation, now poses a serious threat to a number of European agricultural products.
Impact on fruit-growing in South Tyrol
The BMSB has the potential to become the most devastating pest to the most important crops in South Tyrol, a region which presents both the ideal climate conditions for its reproduction and an abundant supply of food such as apples, grapes, pears, plums and cherries. The first adult BMSB in South Tyrol was sighted in spring 2016, when a fruit grower from Naturns spotted the insect on a bucket of paraffin oil originating from the company Bayer. This is not particularly surprising, as it has only ever spread to Europe in goods packaging during transportation. After this encounter, farmers were asked to keep a close eye out for the bug, and other sightings soon followed in the Val Venosta/Vinschgau Valley, the Bassa Atesina/Unterland, Burgraviato/Burggrafenamt and in the Bressanone/Brixen area. Encouraged by the favourable conditions for its proliferation in South Tyrol, the BMSB has since become widespread throughout practically the entire region.
Damage to apple crops
The BMSB wreaks most of its damage by sucking on fruit and leaves. It pierces the fruit with its fine, needle-like mouthparts and then begins to suck out the juice. While doing so it injects an endogenous enzyme into the fruit, which can lead to the deformation or death of the affected parts of the plant. The puncture sites on the fruits or leaves can also lead to secondary fungal damage and subsurface corking. These shortcomings in quality mean that the apples can no longer be sold as fresh produce, which means substantial losses for the farmer.
Control strategies must be developed in order to prevent the BMSB from infesting European agricultural products. As yet, research into how this can be achieved remains in its initial stages; currently, there are a number of options and theories on the matter. One method of minimising the damage caused by the BMSB is to plant trap crops. The theory behind this pest-control strategy is based on providing easily-obtainable alternative food sources: in the area where a main crop is grown (e.g. the apple in South Tyrol), a secondary crop (e.g. soy or sunflower) is grown on a smaller area of land. This secondary crop must be more attractive to the pest than the main crop. The trap-crop can then be treated with pesticides, or a sweep net can be used to trap the bugs. Exclusion netting may also be an effective means of preventing the BMSB from infesting the apple crops. However, if this method is to be used, anti-hail nets are a fundamental prerequisite: The tight-mesh exclusion netting is stitched to the anti-hail netting, and prevent pests from entering the area. In integrated agriculture, chemical pesticides are one of the most effective methods of controlling all forms of pests and diseases. The pesticides which are authorised for use in IP (Integrated Production) agriculture are extremely limited in both efficiency and duration of protection, so preventive measures are of little value. Excessive application of ineffectual insecticides is contrary to the interests of integrated production and also entails additional costs.
The BMSB has numerous natural enemies. Of these, the samurai wasp (Trissolcus japonicas) is the most effective predator. By means of its well-developed chemoreceptors, the wasp follows the “chemical footprint” of the BMSB to their egg clusters, and then lays her own eggs in each egg of the cluster. Samurai wasps hatch from these eggs, parasitizing the entire clutch of brown marmorated stink bugs. A single wasp of just a few millimetres in size can attack up to 42 eggs. The samurai wasp also has a more rapid development cycle than the BMSB and, at a temperature of 25 ° C can reach adulthood after just 11 days. This faculty allows for the hatching of a good number of generations each year. The downside of this strategy is that the samurai wasp is not common to Europe, and the import of non-indigenous animals to the EU is strictly regulated and controlled. Importing exotic insects of this sort could also pose a danger to domestic insect species.
In 2016, the first specimens of BMSB were found in South Tyrol. Nonetheless, the effective economic impact to date has been of limited nature. Over the last few years, however, the bug has expanded its range and become well-established throughout the region. Exactly when and where we can expect an exponential increase in its number remains unclear. In warm years, when increased infestation is likely, farmers will soon have no alternative other than recourse to insecticides. This additional expense of could trigger a downward spiral as broad-spectrum pesticides also weaken beneficial insects, thus increasing the pressure from other pests. The trap-crop method cannot be utilised as a prevailing method due to the limited and, therefore, valuable terrain area in South Tyrol; exclusion netting is extremely costly, and cannot be used on steep slopes. In the long term, natural enemies are the only way to keep the BMSB in check; in their dual role of providing exemplary protection from the BMSB and precluding the use of insecticides, they are an excellent means of promoting sustainable agriculture. Sources: Spektrum, EPPO Global Database, South Tyrolean Advisory Board for fruit and viticulture, SuedtirolNews, Wikipedia