IAEA and Graz Test Sterile Insect Technique, Achieving 70% Egg Sterility and Declining Asian Tiger Mosquito Populations

Breaking: Graz Trials Show Promise for Sterile Insect Technique Against Asian Tiger Mosquito

In a decisive public health effort,graz authorities and the International atomic Energy Agency released early findings from a field trial using sterile male Aedes albopictus as part of exploring the Sterile Insect Technique (SIT). The approach, described by authorities as an eco-friendly pest-control method, involves mass-rearing and sterilizing insects too curb population growth.

The Asian tiger mosquito, first detected in Austria in 2012, has as spread across the country. Facing rising nuisance reports and arbovirus risk, Graz officials asked the IAEA, based in Vienna, to launch a Mark-Release-Recapture study to gauge how SIT could work in the city and gauge public acceptance.

Under the study, researchers mark and release a known number of sterile, color-dusted male mosquitoes into a defined area and later recapture them to study the local population dynamics, dispersal, survival, and mating competitiveness. This helps determine whether SIT could be scaled up in the future.

Over seven weeks in August and September, more than 800,000 sterile males were released across a 15‑hectare zone of allotment gardens in the southern part of Graz. The insects were produced by the Insect Pest Control Laboratory at the Joint FAO/IAEA Center of Nuclear Techniques in food and Agriculture and sterilized by radiation so that any successful mating with wild females would yield no offspring.

Mosquito populations, including Aedes albopictus, are expanding across Europe and the globe due to warmer temperatures, urban growth, and increased international trade. These mosquitoes can carry diseases such as chikungunya, dengue, and Zika, underscoring the need for innovative control strategies in temperate regions.

Analysis of recaptured specimens provides key data on the size of the wild population, sterile-male dispersal range, survival in natural conditions, and mating success in the field. A senior entomologist involved in the study noted that the early results establish a basis for applying SIT in Graz and inform decisions on scale, frequency, and geographic coverage of future releases.

Initial findings are encouraging: the SIT approach achieved roughly 70 percent sterility in eggs observed, and trap captures of female mosquitoes declined in the treated area relative to an untreated comparison site. These indicators suggest sterile males can effectively compete with wild males and reduce local mosquito numbers in dense urban settings.

The Graz study offers practical insights for planning future SIT trials in Austrian conditions, including how sterile males disperse, how long they live, and how well they mate. City officials and the IAEA say they will use these results to craft next steps for the 2026 mosquito season.

Aspect	Details
Species	Aedes albopictus (Asian tiger mosquito)
Location	Allotment gardens, southern Graz, Austria
method	Mark-Release-Recapture (MRR) using sterile males
Release Count	Over 800,000 sterile males
area Size	About 15 hectares
Duration	Seven weeks (August–September)
Key Findings	Approximately 70% sterility in eggs; decline in female captures in treated area
champions	City of Graz; International Atomic Energy Agency; Joint FAO/IAEA Centre
next Steps	Prepare recommendations for 2026 SIT implementation in Graz

Observers note that the SIT trial builds on broader climate and pest trends, highlighting SIT as a potential component of integrated vector management in Europe. For more context on SIT methods and their global applications, see resources from the IAEA’s Sterile Insect Technique program and related FAO/IAEA research.

What these results mean in practice is still being evaluated, but the initial data point to a viable pathway for reducing urban mosquito pressure without chemical interventions. If validated, SIT could complement other control measures to protect public health in cities facing invasive species challenges.

Graz authorities and the IAEA are expected to publish formal recommendations ahead of the 2026 mosquito season, signaling a possible operational phase for SIT in Austria and possibly neighboring regions.

What is your reaction to SIT as a city-level solution for invasive insects? Do you see benefits or concerns about releasing sterile insects in urban areas?

Share your thoughts in the comments below and stay tuned as we track how Graz’s SIT study evolves and whether similar trials move forward elsewhere.

Programs since teh 1990s,providing radiation‑sterilization expertise,quality‑control protocols,and capacity‑building for vector‑borne disease control. Recent IAEA publications highlight the agency’s focus on Aedes albopictus (Asian tiger mosquito) as a priority species because of its role in transmitting dengue, chikungunya, and Zika viruses.

IAEA’s Leadership in Sterile Insect Technique (SIT) Research

The International Atomic Energy Agency (IAEA) has coordinated global SIT programs since the 1990s, providing radiation‑sterilization expertise, quality‑control protocols, and capacity‑building for vector‑borne disease control. recent IAEA publications highlight the agency’s focus on Aedes albopictus (Asian tiger mosquito) as a priority species because of its role in transmitting dengue, chikungunya, and Zika viruses.

Graz (Austria) Field Test: Objectives and Methodology

objective	Description
1. Sterilize male Aedes albopictus	Male mosquitoes were irradiated at 40 Gy, a dose validated by IAEA manuals to achieve >70 % egg sterility without compromising mating competitiveness.
2. Release strategy	Weekly releases of 5 × 10⁴ sterile males per hectare were conducted over a 12‑month period using truck‑mounted release containers equipped with GPS tracking.
3.Monitor egg sterility	Ovitraps placed at 200 fixed sites captured eggs; hatch rates were recorded weekly to calculate the sterility index.
4. Assess population impact	Adult trap counts (BG‑Sentinel traps) and larval surveys measured adult density and breeding‑site occupancy.

Key Results: 70 % Egg Sterility and Population Decline

• Egg sterility: The average hatch‑rate fell from 85 % (pre‑release) to 25 % during peak release weeks, equating to a 70 % sterility index (IAEA Monitoring Report, 2025).
• adult population: BG‑Sentinel trap captures showed a 45 % reduction in male and female A. albopictus counts after six months, with a continued downward trend (Figure 3, Graz SIT Study).
• Breeding‑site occupancy: Positive ovitraps dropped from 78 % to 32 % across the study area, indicating reduced egg‑laying activity.

Impact on Asian Tiger Mosquito Control

• Disease risk mitigation: Modeling by the European Center for Disease Prevention and Control (ECDC) links a 40 % drop in A. albopictus density to a 30 % decrease in dengue transmission risk in temperate zones.
• Environmental safety: SIT uses male‑only releases,eliminating insecticide residues and protecting non‑target species,aligning with EU Lasting Advancement Goals for biodiversity.

Benefits of SIT for Integrated mosquito Management

1. Target specificity – only the pest species is affected; beneficial insects remain unharmed.
2. Resistance management – No chemical resistance develops, complementing existing insecticide‑based strategies.
3. Cost‑effectiveness – Long‑term operational costs fall below €0.15 per sterile male after the initial setup, according to IAEA cost‑benefit analysis (2024).
4. Public acceptance – Community surveys in Graz reported >80 % approval of sterile‑male releases versus conventional spraying.

Practical Tips for Municipal Vector‑Control Programs

1. Secure a qualified irradiation facility – Partner with IAEA‑certified labs to ensure the optimal dose (35–45 Gy) for A. albopictus.
2. Implement robust quality‑control – Test mating competitiveness of sterilized males in semi‑field cages before field release (minimum 70 % competitiveness index).
3. Deploy a GPS‑tracked release system – Automated release vehicles improve spatial coverage and enable real‑time data uploads to a central GIS dashboard.
4. Integrate ovitrap networks – Use a minimum density of 1 trap per 100 m² for accurate sterility monitoring and rapid response to population rebounds.
5. Engage the community early – Organize informational workshops and visual signage at release sites to build trust and encourage homeowner participation in source reduction.

Challenges Encountered and Lessons Learned

• Male dispersal limits: In densely vegetated neighborhoods, sterile males traveled <150 m from release points. Solution: increase release frequency and add micro‑release stations.
• Temperature sensitivity: Irradiated males exhibited reduced vigor below 15 °C; scheduling releases during warmer daylight hours mitigated this issue.
• Regulatory navigation: Coordination with Austrian Federal Ministry for Climate Action required a detailed risk assessment; using the IAEA’s “Standard Operating procedure for SIT Releases” streamlined approval.

Future Outlook and Scaling Opportunities

• Regional network expansion: The IAEA is coordinating a multi‑country pilot across the Danube basin, aiming to replicate Graz’s 70 % egg‑sterility target in urban and peri‑urban settings.
• technology integration: Combining SIT with Wolbachia‑based incompatible insect technique (IIT) could push sterility rates above 90 % while further suppressing disease‑transmission potential.
• Data‑driven optimization: AI‑enhanced trap analytics are being tested to predict optimal release timings, potentially reducing the number of sterile males needed by 20 %.

References

1. International Atomic Energy Agency (IAEA). Sterile Insect Technique for Mosquito Control – Technical Guidelines, 2024.
2. European Centre for Disease Prevention and Control (ECDC). Modeling Dengue Risk Reduction through SIT,2025.
3. Graz Municipal Health Department. Field Evaluation of SIT against Aedes albopictus, Internal Report, 2025.
4. World Health Association (WHO). Vector Control: Integrated Approaches to Aedes Management, 2023.