1. How Tubes of Synthetic Sex Pheromones Reduce Moths in Orchards
Sex pheromones are substances that female insects release to attract males for mating. By synthesizing these pheromones and releasing them into orchards, humans can interfere with the communication and mating between male and female moths, thereby reducing pest populations. This method is called "mating disruption." [1]
For the carpenter moth Endoclita excrescens (ヒメボクトウ), tubes containing synthetic sex pheromones are wrapped around trunks and branches. The guideline is 100 to 150 tubes per 10 ares (about 1,000 square meters). This works out to roughly one tube per 1,000 square meters. [1]
When the scent fills the orchard, males have trouble finding real females. As a result, mating and egg-laying decrease, and the number of moths in subsequent generations gradually drops. The effect is said to last about 3 months. Compared to the 1 to 2 weeks of effectiveness for insecticides shown in the materials, this is calculated to be about 6 to 13 times longer. [1]
Because these substances are originally produced naturally by insects, they have extremely low toxicity to humans and livestock, and there is no concern about residues on crops. This allows for a reduction in insecticides, which helps protect natural enemies of pests. However, this is not a method that makes insects disappear all at once. The reason for this is explored in the next section. [1]
2. Why Pheromone Tubes Take 3 Years to Reduce Orchard Damage
In an apple orchard in Fukushima Prefecture, a demonstration conducted from 2011 to 2013 showed that after 3 years of installing tubes, the proportion of damaged trees decreased from about 30% initially to about 10%. The proportion of damaged trees fell to about one-third. It did not become zero. [1]
The test results from Fukushima Prefecture note two important conditions for using this method. First, if used only in a small area, the effect may be unstable, so it should be used over as wide an area as possible. Second, because the larval period is thought to be 3 years or more, the method must be continued for at least 3 years. [2]
Unlike insecticides, this method works gradually over several years across a wide area. [2]
Is this method special to the carpenter moth Endoclita excrescens, or can it be used for other insects too?
3. Can Pheromone Tubes Work on Other Insects? Only With Species-Specific Pheromones
The answer to "Can it be used for other insects?" is "Only if it is specific to that insect." According to the source, the composition of sex pheromones is said to differ by species in many cases. It is a "cocktail" of several components mixed in specific ratios, and these ratios serve as the species' identifier. [3]
Therefore, the effect of mating disruption is limited to specific species. Corporate product materials list products for several moths that eat fruit trees, such as the peach fruitworm, the pear fruitworm, and the apple leafroller. Tubes for the carpenter moth Endoclita excrescens are not used for other insects; specific products are made for each. [4]
If we compare the composition to a password, it is like each friend’s house having a different password. However, in reality, multiple species may use the same compounds, but they are distinguished by the mixing ratio. Some products intentionally include components to suppress the reaction of non-target species. [3]
Looking at it this way, the method humans use involves investigating the other party’s "language" and creating the same language. So, are there creatures that have been doing this "imitation" with their own bodies long before humans started synthesizing it?
4. How Bolas Spiders Use Moth Sex Pheromone Scents to Catch Male Moths
Bolas spiders (genus Mastophora) release substances that mimic the components of female moth sex pheromones to attract male moths. They catch the approaching males with sticky balls. This method of deceiving prey by imitating their signals is called aggressive chemical mimicry. [5]
It is reported that three components of moth sex pheromones were detected from adult females of the species M. cornigera. [5]
Do they change their scent during the night? In another species, M. hutchinsoni, more than 90% of their prey were two types of moths (family Noctuidae) that are active in the early and late night. Research suggests the possibility that the spider changes the scent it emits during the night to match the prey active at those times. This is reported as a research possibility, not a definitive fact. [6]
It appears that spiders use a method that humans only recently put into practical use, using their own bodies. So, what about plants that do not eat insects?
5. How Ophrys Orchids Use Shape and Scent to Imitate Female Bees
Orchids of the genus Ophrys, which grow in Europe, attract males with shapes and scents similar to female bees. Males land on the labellum (lip) of the flower and approach it, thinking it is a female. [7]
During this time, pollen masses stick to the male’s body. The male then goes to the next flower and carries the pollen. A key feature is that the flower does not offer nectar and takes advantage of the insect’s mating behavior. [7]
Research indicates that the flower’s scent is the main cue triggering the male’s mating behavior. Like the spider that calls male moths, the "scent of the female" seems to be the deciding factor. [7]
6. How Kinryohen Orchids Imitate the Japanese Honeybee's Aggregation Pheromone
Research suggests that the flowers of Kinryohen (a type of Cymbidium) emit a scent that mimics the aggregation pheromone of the Japanese honeybee, attracting the bees. [8]
In another research project (Grant-in-Aid for Scientific Research, 1994–95), it was reported that an orchid (Cymbidium pumilum) emits the same compound (linalool oxide) as the aggregation pheromone used by honeybees to call their companions. It is said that a 10-nanogram sample was able to attract honeybees. 10 nanograms is one hundred-millionth of a gram. The project describes it as early evidence that plants use these pheromones for pollination. [9]
These two examples involve different species and different substances, so they should be read separately. [9]
7. Three Kinds of Scent Imitation and What to Look For Near Orchards and in Documents
So far, we have seen three forms of scent imitation: mating disruption spread in orchards by humans using synthesized chemicals, prey-collecting scents emitted by spiders using their own bodies, and love or gathering scents emitted from orchid flowers. All share the point that they are possible because the imitator knows the "language" that the other party reacts to.
Try this. When you pass near an orchard, look at the trees from the road and see if you can spot thin tubes hanging from trunks or branches. Many orchards do not use them, so it is not strange if you do not find any. If there is no orchard nearby, you can look at photos in the National Agriculture and Food Research Organization (NARO) materials to see how the tubes are wrapped. Do not enter the orchard or touch anything. [1]
If you want to know more, reading NARO’s "Trivia 11: Controlling Moths with Sex Pheromones" provides the numbers from the Fukushima demonstration. Since the spider’s night-time switching is still at the "possibility" stage, comparing what has been verified in papers can lead to new questions. [1]