The feasibility of the sterile insect technique (SIT) as a malaria vector control strategy against Anopheles arabiensis has been under investigation over the past decade. One of the critical steps required for the application of this technique to mosquito control is the availability of an efficient and effective sex-separation system. Sex-separation systems eliminate female mosquitoes from the production line prior to irradiation and field release of sterile males. This is necessary because female mosquitoes can transmit pathogens such as malaria and, therefore, their release must be prevented. Sex separation also increases the efficiency of an SIT programme. Various sex-separation strategies have been explored including the exploitation of developmental and behavioural differences between male and female mosquitoes, and genetic approaches. Most of these are however species-specific and are not indicated for the major African malaria vectors such as An. arabiensis. As there is currently no reliable sex-separation method for An. arabiensis, various strategies were explored in an attempt to develop a robust system that can be applied on a mass-rearing scale. The progress and challenges faced during the development of a sexing system for future pilot and/or large-scale SIT release programmes against An. arabiensis are reviewed here. Three methods of sex separation were examined. The first is the use of pupal size for gender prediction. The second is the elimination of blood-feeding adult females through the addition of an endectocide to a blood meal source. The third is the establishment of a genetic sexing strain (GSS) carrying an insecticide resistance selectable marker (dieldrin-resistance rdl gene and/or other GABA receptor antagonists that can be used as alternative insecticides to dieldrin) or a temperature-sensitive lethal marker.

Background: Effective entomological surveillance is crucial for malaria control, especially in low transmission settings. This study aimed to compare the performance of three mosquito collection methods (clay pots, carbon dioxide (CO₂)-baited tents, and human landing catches (HLC)) for malaria vector surveillance in the low transmission area of Nkomazi, South Africa. Methods: From March 2019 to March 2020, adult mosquitoes were collected monthly from three different sites over five consecutive nights and mornings. Each collection method was used at each site to capture both outdoor resting and host-seeking mosquitoes. The collected mosquitoes were morphologically identified to the Anopheles genus and species, followed by confirmation using molecular PCR assays. The species composition, relative abundance, and diversity were evaluated, and statistical tests, including Kruskal–Wallis and ANOVA, were used to assess differences in abundance and diversity across collection sites and methods. A Generalized Linear Mixed Model was applied to assess the impact of various factors on species abundance. Results: A total of 1337 Anopheles mosquitoes were collected, with 98.5% being females. CO₂-baited tents yielded the highest number of mosquitoes (57.6%), followed by HLC (39.1%) and clay pots (3.3%). Species composition included 52.4% of the Anopheles gambiae complex and 13.6% of the Anopheles funestus group. While species richness varied significantly between collection methods, with CO₂-baited tents showing the highest richness, no significant differences were observed in abundance across sites or methods. The clay pot method was associated with significantly lower species abundance compared to HLC and CO₂-baited tents. Species abundance fluctuated across months, with February and November showing a higher record. Males were less prevalent than females. Additionally, species abundance was lower in Block C and Vlakbult compared to Block A. Conclusions: This study highlights the importance of choosing appropriate mosquito collection methods based on specific entomological indicators and transmission dynamics. While CO₂-baited tents provided the highest species richness, clay pots, despite yielding fewer mosquitoes, are effective for capturing outdoor resting malaria vectors. These findings suggest that a combination of collection methods is essential for inclusive malaria vector surveillance, facilitating tailored strategies for effective malaria control and resource optimization.

Malaria remains a major public health challenge in sub-Saharan Africa, with Anopheles arabiensis an important vector in several regions. Increasing insecticide resistance and flexible vector behavior limit the effectiveness of conventional control measures. The sterile insect technique (SIT) offers a complementary approach through the release of sterile males, with program success dependent on male quality. This study assessed the effects of chilling, fluorescent dust marking, and X-ray irradiation on the quality of laboratory-reared male An. arabiensis. Adult males were assigned to six treatment groups combining chilling, irradiation, and marking in different sequences. Male quality was evaluated through recovery, escape rates, reproductive performance, and longevity under standard insectary conditions. Recovery rates one-hour post-treatment were high across all groups (93.5–96.6%) and did not differ from controls. Escape rate was temporarily reduced at two hours but largely recovered by 24 h, with only chilled and marked males showing persistent impairment. Fecundity and female insemination rates were unaffected by treatment. Fertility remained high in non-irradiated groups and was reduced to < 0.2% following irradiation. Longevity was not significantly affected. These results indicate that male An. arabiensis are resilient to routine SIT handling procedures. Brief chilling followed by irradiation and marking preserves key quality traits, supporting optimized operational protocols for SIT-based malaria vector control.

Bushbuckridge, South Africa, remains a challenging setting for malaria elimination due to residual transmission and diverse Anopheles populations. This study assessed Anopheles species diversity and insecticide susceptibility across 29 localities between 2022 and 2024. Morphological and PCR-based identification revealed 18 taxa, primarily Anopheles pretoriensis, An. quadriannulatus, and An. rufipes, and the primary vector An. arabiensis accounted for 7.1% of collections. Two putative An. arabiensis/An. quadriannulatus hybrids were detected, warranting further genomic investigation. While vector populations were largely susceptible to DDT, deltamethrin, and pirimiphos-methyl, reduced DDT susceptibility was observed in the An. funestus group; however, due to small sample sizes, this result remains inconclusive. These findings underscore the necessity of sustained, integrated vector surveillance to inform strategic control in complex transmission landscapes.