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202108 Hortgro Newsletter Blue Bug2

Is Something Bugging Your Orchard?

Get it identified at Blue Bug Diagnostic Service.

By Anna Mouton

Effective pest control starts with knowing exactly what you are fighting. Incorrect assessment of the cause of damage can lead to expensive errors in pest management. This risk is magnified in the case of emerging or invasive pests.

“If a grower finds a bug that he doesn’t know or hasn’t seen before, then he needs support to be able to identify it as soon as possible so that he can take appropriate action,” says Chris Jurisch, agricultural advisor at ArborTech. “I think it’s an essential part of the whole fruit-growing business — you can’t farm without knowing your enemy.”

Hortgro recognises the challenges growers face when confronted with a nondescript worm inside a rotting fruit or with some minuscule insect glued to a trap. This is why they have teamed up with SATI and Winetech to contribute funding for the insect identification service — Blue Bug Diagnostic Service — at Stellenbosch University.

What is Blue Bug Diagnostic Service?

The need for an insect identification service was first recognised more than a decade ago by Prof Pia Addison of the Department of Conservation Ecology and Entomology at Stellenbosch University. Faced with requests for insect identification, Addison obtained support from the industry to establish what has become Blue Bug Diagnostic Service.

The diagnostic service is not limited to the identification of insects. It includes identification of mites and analysis of bud mites on pome and other fruit. Users can also submit plant material or damaged fruit.

“For example, if someone brings me a damaged apple, I’ll cut it open and see what I find,” says Caro Kapp, an entomologist with Blue Bug Diagnostic Service. She can identify larvae of certain pests like codling and false codling moths by examining them under the microscope. But most larvae pose a bigger challenge.

“Fruit-fly larvae all look the same,” explains Kapp. “You can’t identify them morphologically.” The same is true of many other larvae. If the larvae are alive, Kapp attempts to rear them in the laboratory, because the adults will have distinctive features that facilitate their identification.

When larvae are dead, or the adults enigmatic, Kapp can resort to DNA analysis. The identification of anything suspected of being invasive is also confirmed by DNA analysis. Bugs that prove especially hard to identify are referred to an appropriate expert.

For codling and false codling moth, Kapp can perform degree-day analysis on larvae. She measures the head capsules of the larvae to determine their stage of development and assesses this relative to temperature data from the site where the larvae were collected.

“I can tell the grower in which week the infestation occurred,” says Kapp. “Then they can go back and see whether something went wrong in their control programme.”

Despite the name, Blue Bug Diagnostic Service provides more than just diagnostics. Prior to COVID-19, they held courses on topics ranging from moth identification to mass rearing of insects. They are available for consulting, and they support research projects, for example by analysing trap catches.

How can growers access the services?

Users can submit either plant material or bugs. “If they send the insect itself, they must put it in surgical spirits,” advises Kapp. “Not the purple stuff — methylated spirits break up the sample and you can’t get any DNA from it.”

Surgical spirits are 70% alcohol and should be available from any pharmacy. Hand sanitiser also works, according to Kapp. “If you can’t get hold of those, then use the highest percentage alcohol you can find, preferably 70% or higher alcohol. Witblits will work.” Kapp has even received samples in gin.

Although many people send photos of bugs for identification, Kapp warns that this is not optimal. “It’s very difficult to identify something from a photo, especially moth larvae. You can’t just look at it and say what it is.” Besides the lack of detail on photos, there is no opportunity to rear the insect or to extract DNA.

Kapp stresses that users must complete a sample submission form — available on the Stellenbosch University website. The information on the form helps her to make a correct identification. She also captures the information in a database. “So, for example, if someone asks how much codling moth there is an area, I can look it up and tell them,” says Kapp.

Most of the samples submitted to Blue Bug Diagnostic Service come from the Western Cape, but Kapp does receive requests from other provinces. About a quarter of the samples she has processed during the past three years have been of pome and stone fruit, and 90% of all samples are agricultural, including everything from pecans to pomegranates.

“I have also received weird samples, like pillows,” relates Kapp, who makes it clear that she prefers sticking to agricultural samples.

The turnaround time for a result can be as little as one day, such as in the case of microscopic examination of a codling or false codling moth larvae. “If I need to rear a larva, the turnaround time depends on its life cycle,” says Kapp. “Or if I need to send samples for DNA analysis, it takes about two weeks.”


Blue Bug Diagnostic Service remained fully operational during COVID-19, but Kapp saw a reduction in sample submissions. Their busiest period is usually in summer when the warmer weather favours insects, and the deciduous-fruit industry is in full swing. Samples can be delivered in person or by courier to Kapp at the Department of Conservation Ecology and Entomology in the JS Marais Building or dropped at the Disease Clinic in the Lombardi Building. Both are in central Stellenbosch.

For more information on Blue Bug Diagnostic Service, or to request a price list or submit a sample, contact Caro Kapp at

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