Kicking off a stink bug
Japanese researchers have used UV-Vis and nuclear magnetic resonance spectroscopy to help them develop a potential repellent for the invidious stink bug, an invasive pest species that has been spreading rapidly through the USA, invading homes and damaging crops.
Stink bugs, a superfamily of insects in the Heteroptera suborder of Hemiptera produce a foul odour as a defensive mechanism when attacked by predators. Glands in their thorax between the first and second pair of legs release offensive aldehydes such as hex-2-enal. These herbivorous insects also commonly known as shield bugs because of their shape have sucking mouthparts with which they will render fruits, vegetables, and other crops susceptible to bacterial and fungal attack by opening up an entry point. For example, stink bugs cause "pecky rice" or kernel spotting. In Japan there are ten species that affect rice, soybean and fruit crops.
Repelling rice-piercing bugs
Halyomorpha halys, the brown marmorated stink bug is native to mainland China. It was accidentally introduced into the United States in the mid-1990s and has become a significant crop pest, piercing peaches, apples, green beans, soybeans, cherry, raspberries, and pears from late May onwards.
Synthetic insecticides currently used in Japan include neonicotinoids (dinotefuran, nitenpyram, and imidacloprid), organophosphates (fenitrothion and phenthoate), and pyrethroids (silafluofen and ethofenprox). However, their application leads to insecticide-resistance in the pests and has the potential to disturb ecosystems. An alternative approach is to use attractants or repellents to control the pest. Some pheromone attractants for various species have been identified but no repellants have yet been identified.
Now, Hiromitsu Nakajima, Atsushi Ishihara, Yuji Sawa and Emi Sakuno of the Department of Agricultural Chemistry, Faculty of Agriculture, Tottori University, in Koyama, Tottori, Japan, have sought out a new and natural repellent among secondary metabolites produced by fungal endophytes. The team explains that the endophytes live within plants and show no external signs of infection, which implies they are non-toxic to the host plants.. Such a symbiosis presumably imparts an advantage on both endophyte and host plant allowing the plant to tolerate stresses such as drought, disease, and insect pests, and from the scientist's perspective offers a potential lead for a stink bug repellant.
The team has investigated the stinkbug, Eysarcoris ventralis (Westwood), as a test insect. "Although E. ventralis has been reported to be a rice pest, Stenotus rubrovittatus (Matsumura) and Leptocorisa chinensis (Dallas) are much more common and notorious pests in Japan. We chose E. ventralis as a test insect only because it is much easier to collect, maintain, and handle in the laboratory, Nakajima told SpectroscopyNOW. The team extracted from various cultures of grass weed endophytes and in their screen identified an extract from the green foxtail (Setaria viridis (L.) Beauv.) that had a repellent effect. Spectroscopy revealed the active compound to be 3-(4-methylfuran-3-yl)propan-1-ol. They have now published data on the repellant's activity and the effects of four acyl derivatives of this compound.
Bugs bottled
In their research, they discovered an advantageous characteristic of the insect that made developing a screening method relatively simple. When left in the cool, the insects prefer to aggregate in the dark. The assay apparatus thus involved two dark holes composed of glass bottles: a piece of filter paper containing a test sample in one bottle and a piece of filter paper containing no sample in the other. They introduced twenty stink bugs collected from the campus on to the filter paper and left them to wander into a dark hole, or not as the case may be. After half an hour, almost three-quarters of the insects had moved into a bottle; the remainder stayed out of the holes. By comparing the respective number of insects found in the two holes, the team was able to ascertain the repellent activity of the sample applied.
One particular derivative was found to be most effective and has potential as an effective alternative chemical for controlling stink bugs. Experiments to assess its effect in pots and in the field will soon be underway.
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
|
|
