author(s)
Hugo Ribeiro, Martín Ribeiro, Maria Do Rosário Jorge and Joana Estrada

abstract
The expansion of invasive mosquito species across Europe has raised growing concerns for public health, particularly due to their role in transmitting diseases such as dengue, Zika, and chikungunya. Effective surveillance strategies are essential to detect and monitor mosquito populations and guide vector control measures. Ovitraps are widely used for monitoring mosquito eggs, but their sensitivity is strongly influenced by the type and preparation of the oviposition substrate. This study aimed to evaluate the effectiveness of three surface treatments applied to wooden tongue depressors used as oviposition substrates in ovitraps: no scraping, superficial scraping, and deep scraping. Over a seven-week period in a peri-urban setting in southern Portugal, 147 wooden spatulas were deployed across seven ovitraps. Egg counts were recorded and analysed statistically to determine the impact of each scraping method on egg recovery. Results showed that deep scraping consistently yielded significantly higher numbers of mosquito eggs compared to the other treatments. The technique increased egg recovery by a factor of approximately fifteen compared to untreated spatulas and by four compared to superficial scraping. Deep scraping also produced a higher proportion of medium and high egg concentration samples, indicating improved oviposition attraction and retention. Statistical analyses confirmed the robustness of these findings across multiple traps and weeks. This study highlights the critical role of standardised deep scraping in enhancing ovitrap sensitivity and improving the reliability of entomological surveillance data. By maximising egg detection, deep scraping contributes to more accurate assessments of vector abundance and supports early warning systems for vector-borne disease outbreaks. The technique is low-cost, easy to implement, and particularly suited to routine monitoring in both high- and low-resource settings.