Cape Town – A couple with a love for insects has been inseparable since their second year of study at Stellenbosch University. They have now also received their doctoral degrees together during the Faculty of AgriSciences’ graduation ceremony on Tuesday.
To top it all, Vernon and Leigh Steyn both studied different methods of controlling pesky moth pests. Vernon did research on the false codling moth, while Leigh focused on the Cape grapevine leafminer.
Their love story dates back to the winter of 2011, when both were in their second year of BSc studies in the Faculty of AgriSciences. Vernon had missed a few classes, and was desperate to find out what he needed to study for a scheduled test.
"After class a girl, I did not know, spontaneously and kindly started helping me and provided the information that I needed. And that was it!"
Vernon explains how they met. Within weeks they started dating. The pair have since completed their studies side by side and married in May 2017.
Vernon acknowledges that it is thanks to Leigh that he developed an interest in insects: “She has the wonderful ability to notice the smallest insect in the veld or even when we are just walking in town.”
An eureka moment in their academic careers came when they attended classes together in their fourth year on insect behaviour and development. It was presented by the well-known entomologist Prof Henk Geertsema.
"We hung on every word he said, and for the first time truly realised just how interesting and important the world of insects was," Leigh recalls.
After receiving their undergraduate degrees, both embarked on their MSc studies on particular agricultural pests. Vernon studied the Mediterranean fruitfly, while Leigh focused on the Cape grapevine leafminer. This insect was also the subject of Leigh’s subsequent doctoral studies.
At 28 and 27 respectively, Vernon and Leigh are the first of their initial first-year class to complete their doctoral studies. Both are star students who received numerous awards for their academic achievements during their course of their studies. Last year Leigh presented one of the five best student posters at the European Congress of Entomology in Italy.
In 2009 Leigh matriculated at Rhenish Girls’ High School in Stellenbosch. She is not only passionate about the environment, but has also passed advanced ballet exams. She likes fishing on the Wild Coast, insects, snakes and reptiles, and is passionate about animal rights and the eradication of alien plants. Together with her parents she has for many years been a member of Friends of Stellenbosch Mountain, a group dedicated to eradicating alien plants on Stellenbosch Mountain.
Vernon has subsequently also become part of the group, and has been chairman since 2018. He matriculated in 2008 at Vereeniging High. Earlier this year he started working for the Cape branch of Insect Science in Tzaneen. As a senior field scientist he focuses on developing environmentally friendly methods, such as mating disruption, to control various agricultural pests.
What did Vernon study?
As part of his doctoral degree, Vernon looked at various biological methods that farmers can use to control false codling moth (Thaumatotibia leucotreta) in stone fruit orchards and in vineyards. The larvae of this moth can cause unsightly damage to fruit and is a problem when it comes to exporting fruit.
"In the past, farmers have unsuccessfully tried to control the pest using insecticides and because of their damaging impact on the environment and on human health new ways of combating the moth must be found," he explains.
Vernon looked at the impact of various types of insect-specific entomopathogenic nematodes and fungi on the pest. He found that it is particularly effective to use nematodes during the moth’s larval stage.
"The entomopathogenic nematodes kill the larvae within 48 hours and persist within the soil for four weeks after being sprayed," he explains.
He also investigated the use of female pheromones to disorientate male moths. The method has been in use for several decades. Vernon’s studies are, however, the first to show exactly how this effective this method works and influences the behaviour of the moth. He found that in up to 99% of cases, the male moths become so disorientated that they cannot locate females. In the process, the insect’s reproductive cycle is completely overturned.
"It even works well in orchards and vineyards where a lot of these insects occur," he says.
"By using different techniques at each stage of the life cycle of the pest, it is possible to control false codling moth successfully," Vernon reckons.
He completed his studies under supervision of Dr Pia Addison, Prof. Antoinette Malan and Dr Daleen Stenekamp of Stellenbosch University’s Department of Conservation Ecology and Entomology and HORTGRO Science. Funding for the work was received from HORTGRO Science and the South African Table Grape Industry (SATI).
What were Leigh’s studies about?
Leigh’s doctoral work is a continuation of her master’s degree studies on a small indigenous moth, the Cape grapevine leafminer (Holocacista capensis). With a wingspan of about 4 mm, it is about the size of one rice grain. It was first reported in 2012 in South African table grape vineyards. Over the past few years it has become a problem, especially in the Berg River region.
When infestations are high the moth’s cocoons can be found on grape bunches. To be acceptable for the export market labourers must remove these cocoons by hand in packing stores once bunches have been harvested. To date, no insecticides have been registered for the control the insect in table grape vines.
As part of her research, Leigh began to develop a management plan that can help growers control the moth. This includes biological control methods that can be used in conjunction with a moderate level of chemicals. Leigh has, among other things, found that three types of entomopathogenic nematodes that naturally occur in the soil attack the larvae while it develops within a grapevine leaf. She also found that bunch covers work well to prevent the cocoons from landing on the grape bunches. This means that the fruit is suitable for export.
"The study shows that it is possible to appropriately control population numbers in commercial vineyards by integrating chemical, physical and biological control methods," she says.
Her studies were completed under the supervision of Dr Pia Addison and Prof Antoinette Malan of Stellenbosch University’s Department of Conservation Ecology and Entomology. Leigh’s project was supported by the South African Table Grape Industry (SATI) and the National Research Foundation (NRF).