Biosecurity and bugs

A 16-year quest to identify a mite intercepted on Italian kiwis highlights critical challenges in biosecurity systems. By Dane McDonald.

Entomologist Dr Davina Saccaggi of Citrus Research International illustrated the challenges of navigating international biosecurity by recounting the story of a mite that had eluded identification by the local phytosanitary community for 16 years.

When first intercepted on kiwis from Italy, the flat mites resembled the citrus flat mite (Brevipalpus lewisi), a quarantine pest approximately 0.2 mm in size, reddish-orange, and oval-shaped, with piercing mouthparts used to extract plant juices.

Flat mites can be a significant problem for growers. These mites damage plants directly, and some transmit plant viruses.

After the first interception from Italy, specimens were also recorded on imports from other European countries. Why did this critter manage to evade identification for more than a decade?

Factors complicating species identification

Saccaggi provided three key reasons for the identification challenges. Firstly, only adult mites were intercepted, raising the question: was kiwi a host or just a coincidence?

Secondly, the taxonomy of Brevipalpus mites is highly complex, making it difficult to determine if the intercepted mites were a new species or one of the approximately 300 already described.

“One reason we couldn’t figure it out is that there are no local specimens for comparison,” explained Saccaggi. “If you intercept something, you only have what’s at hand for comparison. If it is not an organism from South Africa, there’s nothing to easily compare it to, especially without breaking confidentiality.”

Thirdly, the sensitivity and confidentiality surrounding phytosanitary information posed a significant hurdle. Saccaggi could not seek assistance from overseas experts. However, her breakthrough came in 2023 when Italian researchers surveying kiwifruit identified a new Brevipalpus species.

The Italians contacted Saccaggi due to her mite expertise, and the team identified the mystery mite as Brevipalpus garmani.

According to Saccaggi, the process could have been expedited through better collaboration and systems for sharing information confidentially.

“I’m not advocating sharing with everyone, but keeping information so confidential that you cannot get an answer is hamstringing science in biosecurity,” she said.

Outdated quarantine tools and increasing trade

On paper, South Africa’s biosecurity is well-regulated with robust international systems and trade agreements, but Saccaggi is concerned about often limited capacity and possible inefficiencies.

Some quarantine departments use outdated methodologies despite dramatically increasing trade volumes. “This is not just a problem in South Africa. This is a global issue,” she said.

Furthermore, while interceptions of quarantine pests are tracked, it’s unknown how many non-quarantine pests are intercepted, how many consignments are inspected per interception, and how large each consignment is.

This information is often buried in trade records or shipping manifests, making assessing the system’s effectiveness hard. Saccaggi said this complicates determining the true efficacy of biosecurity measures.

To improve the biosecurity framework, Saccaggi meticulously studied more than 26 000 samples that passed through the DALRRD diagnostic laboratory over 25 years. The records showed that mites, insects, and fungi were most commonly intercepted.

The small size of these organisms allows them to slip through quarantine more easily. Successful interceptions depend on well-trained personnel and specialised equipment to detect and identify them. Saccaggi pointed out that an inspection at the harbour without a microscope “is simply not going to cut it.”

Rethink reliance on inspections

“Firstly, and this may seem counterintuitive, don’t rely solely on inspections,” said Saccaggi. “Biosecurity inspections are designed to verify that the system is functioning properly, not to serve as the primary biosecurity mitigation measure. Unfortunately, we often treat them as the entire biosecurity strategy, which they shouldn’t be.”

She believes the focus should be on systems approaches, mitigation measures, and ensuring that orchards are clean and postharvest procedures optimised.

“There needs to be more investment in training to ensure that personnel know what they are looking for and are using the proper methodology,” she emphasised.

“Far too often, a visual inspection was conducted, and no fungi were seen. But how can you expect to see fungi in a box stored in a cold facility that has just arrived in the country? This is not an effective detection method.”

Saccaggi explained the importance of the pathway by which pests are introduced. Studying individual organisms only gives a limited risk analysis of the whole pathway and is useless for unidentified or unintentional species with unknown risks.

For instance, conducting a risk analysis for intentionally importing an ornamental plant is beneficial. However, since new pests are not intentionally imported, pest-risk assessments should be integrated into pathway-risk assessments rather than focusing solely on individual pests.

Pathway-risk assessments inform the holistic management of pathways rather than targeting individual species with legislation. Each pathway needs a unique examination, as one solution may not fit all scenarios.

She has also developed predictive models to inform inspections. “By targeting samples likely to have contaminants, we can achieve better results with less effort,” she said.

“If we use these predictive models to inspect only the most risky 10% of consignments, we still improve the detection rate by 40%. This means a 90% reduction in workload with an increase of 40% in effectiveness.”

Lastly, Saccaggi noted that the system’s effectiveness relies heavily on well-trained, motivated biosecurity inspectors. “So more than anything, you need to invest in people,” she concluded.

Watch Saccaggi’s presentation on the Hortgro YouTube channel.