Barcoding alien invertebrates and biological control agents in South Africa, with a focus on the natural enemies of Thaumatotibia leucotreta (Meyrick)

1. Review the DNA barcoding status of alien invertebrates and biological control agents in South Africa;
2. Investigate the presence of Thaumatotibia leucotreta parasitoid wasps in organic and IPM orchards within the Western Cape and barcode all sampled parasitoids; and
3. Determine the critical thermal limits of Trichogrammatoidea cryptophlebiae in the laboratory.

1. South African alien invertebrate data were compiled from literature and databases (GBIF, BOLD, GenBank) through July 2023, and analysed using R software.
2. Field sampling occurred in Western Cape orchards (November 2023-February 2024) using coloured pan traps with sentinel eggs and fruit collection. Wasp specimens were morphologically identified and DNA barcoded using COI sequencing.
3. Laboratory thermal tolerance experiments used parasitised eggs from a commercial insectary, with critical thermal limits measured using a custom thermal stage at 0.1°C/minute ramping rates on 45 individuals each for minimum and maximum temperatures.

1. Major gaps in DNA barcoding were identified, particularly among arachnids and platyhelminths. Whilst 66.8% of alien invertebrate species were accessioned on BOLD, only 24.3% represented South African specimens, and 44.6% lacked accompanying images.
2. No T. leucotreta parasitoids were sampled in Western Cape orchards despite ideal conditions, suggesting low population densities or suboptimal methodology. This absence indicates natural populations may be insufficient for pest control.
3. Critical thermal limits of T. cryptophlebiae were 8.15°C ± 0.58°C (minimum) and 44.50°C ± 0.41°C (maximum). The minimum exceeded the wasp’s previously reported developmental threshold (7.65 °C), indicating adult wasps are less cold-tolerant than other life stages.

The lack of T. leucotreta parasitoids sampled in Western Cape orchards, despite optimal sampling conditions, suggests natural biological control may be inadequate, necessitating augmentative approaches. The thermal tolerance data for T. cryptophlebiae provide essential baseline information for predicting distribution shifts under climate change. These findings collectively demonstrate the urgent need for comprehensive baseline genetic and physiological data to support evidence-based pest management strategies in a changing climate. This study also reveals critical knowledge gaps hindering effective management of alien invertebrates and biological control agents in South Africa. The substantial deficiency in DNA barcoding data, particularly for South African specimens, severely limits species identification capabilities.

Given the potential lack of FCM parasitoids other than T. cryptophliae in the Western Cape, the industry could consider investing in research on other parasitoids, such as Agathis bishopi. Further efforts should be made to sample wild populations of other species listed in the literature and those mentioned in Moore (2002) (available at https://core.ac.uk/download/pdf/145047508.pdf). T. cryptophlebiae‘s thermal limits (8.15-44.50°C) should aid more effective release regimes.