Insect Science is the only private semiochemical company with a laboratory in Southern Africa delving into the chemistry of the pheromones and other semiochemicals of insects found in local orchards. Many invertebrates rely on smell to sense their external environment through the receptors on their antennae. Pheromone signals are as unique to different insect species as fingerprints to humans.
Insect Science's three chemists and many field researchers are cracking insect pheromone codes to identify and artificially mimic these chemical signals in order to monitor and control insects regarded as pests.
A mural at Insect Science's Tzaneen campus, executed by artist Serge One of Luna Nova
Insect control through naturally-produced compounds
Controlling insect behaviour with pheromones results in lower collateral damage to the broader invertebrate population compared to broad-spectrum insecticides.
It differs fundamentally from insecticide spraying in that it relies on compounds that adults of the targeted insect population naturally produce. The individuals in the population consensually engage with Insect Science's pheromone products rather than their pheromone-producing counterparts.
Moreover, the development of resistance to toxic chemical sprays remains a possibility, but no insect will become resistant to its own pheromone. From the false codling moth on citrus to the invasive tomato leaf miner, Insect Science has narrowed down which pheromones make the insects tick.
Fingerprinting pheromones
Dr Marc Bouwer, an analytical chemist with an interest in chemical ecology, samples the pheromones released by the insects that are reared on the company's premises in Tzaneen. Dr Bouwer then separates the compounds in the sample and pinpoints the pheromone by measuring the resistance across the male's antennae. "As soon as the pheromone hits the receptors in the male's antennae, neurons open ion channels, and you see a drop in antennal resistance. This tells us where to look for the pheromone in a sample," he says.
Analytical chemist Dr Marc Bouwer isolates and identifies pheromones of South African insects
He then analyses the pheromone sample in a mass spectrometer. This system bombards the pheromone compounds with electrons that fragment the pheromone molecules into positive ions with different masses that are weighed and counted. The data is assembled into mass spectrum patterns that are like unique codes for different compound identities. A tentative identification of the pheromone can then be made, based on the compound's fragmentation pattern found in a database.
Unknown compounds are also identified with the nuclear magnetic resonance (NMR) spectroscopy technique which provides spectra that enable the chemists to determine the chemical structure unequivocally.
Pheromone synthesis
Once the chemists have a tentative identification, the process to synthetically manufacture the pheromone starts. Some synthetic procedures can take a very long time to develop and scaling up to commercial quantities can be a challenging task. That is why most of Insect Science's chemists work in the pheromone synthesis department.
Dr Divan van Greunen, synthetic chemist at Insect Science
The potency of pheromones is thus that some product lines require only a single gram for an entire season's manufacturing, making it worthwhile to develop and own the synthesis process, notes Dr Steyn, the managing director of Insect Science. "This is especially true if a pheromone has never been identified or synthesised anywhere in the world but at Insect Science."
In other cases, large amounts of pheromones are needed for the dispensers that are used for mating disruption. This mechanism is very effective and used in many of South Africa's fruit and nut orchards.
Registered commercial products are also continually tested. "We monitor how lures release pheromones and we quantify the release rate. In this way, we know how much is released in the field and we can control insects in an environmentally friendly way if one compares that to spraying toxic pesticides in the field," Dr Steyn explains.
Left, a McPhail trap and right, Last Call™ F.F. applied in the field against fruit flies
Polyphagous shothole borer
Insect Science has synthesised quercivorol, an alcohol-based aggregation pheromone released by the female polyphagous shothole borer (Euwallacea fornicatus). The beetles use the quercivorol compound to attract more female beetles and form colonies in trees, ultimately overpowering the tree's natural defences. These beetles are known to carry and transmit the Fusarium euwallaceae fungus, leading to tree infection, branch die-back, and potentially tree death.
"It's imperative not to place quercivorol lures in an orchard as it is a super potent attractant for beetles. The lures should rather be deployed in traps on the outside of the affected orchard at a height of 1.5 m. This effectively lures the beetles out of the orchard," Dr Steyn remarks.
Insect Science has released P.S.H.B. PheroLure®, a superior lure used to monitor and trap the females of the invasive beetles, whose risk to suburban and agricultural trees could be devastating if not cataclysmic.
A light design inspired by the molecular structure of quercivorol, emitted by polyphagous shothole borer females to call more to a besieged tree, made by Rhino Construction
According to the company, the field efficacy of the Insect Science P.S.H.B. PheroLure® has been proven to sustain catches for at least twelve weeks during summertime conditions. This lure is now also available in Australia.
Insect Science is also investigating the repellents that female shothole borer beetles release when a tree is overpopulated. This signal effectively repulses beetles from the infested tree, for a potential double-barrelled push-pull technique to control the polyphagous shothole borer.
For more information:
Dr Vernon M. Steyn
Insect Science®
Tel: +27 15 065 0199 or +27 83 960 2153
https://insectscience.co.za/