# Herring-Based Diets Provide Robust Support for Anopheles gambiae Development and Colony Maintenance

## TL;DR

This study shows that dried herring can be used as a cost-effective and sustainable alternative to commercial feed for raising Anopheles mosquitoes in labs.

## Contribution

The study introduces herring-based diets as a viable, locally available alternative to commercial feeds for mosquito rearing.

## Key findings

- Herring-based diets supported the best larval survival and adult emergence rates.
- Maize-based diets led to higher mortality and poor pupation rates.
- Herring combined with maize improved mosquito development and fecundity.

## Abstract

The maintenance of mosquitoes in the laboratory is important for vector biology research. Obtaining healthy adult mosquitoes starts with ensuring that the larvae are fed well. The established standard protocols, however, suggest the use of feeds that are usually commercial, presenting procurement challenges for laboratories, particularly in low-resource settings. Therefore, this study assessed the use of local produce, including maize, beans, and dried herrings, as feed for mosquito larvae. We tested how well these feeds supported the development of the larvae, and tested their effect on adult size, weight, and the ability of the female adult to reproduce the next generation of offspring. Our results showed that herrings performed best among all feeds tested and were comparable to the commercial feed. Although beans often resulted in lower estimates, the negative effect could be reduced with the addition of herrings. We conclude that herrings alone or herring-based feeds that are readily available, cheap, and sustainable can be used in laboratory maintenance of Anopheles mosquitoes. Further studies can improve on this by standardizing proportions of herring and maize and/or bean feed combinations for optimal mosquito maintenance for research.

Laboratory maintenance of mosquitoes is important for studying vector biology and transmission of diseases, and for testing vector control tools. Standard operating procedures require feeding larvae with commercial fish meal. However, for many insectaries in sub-Saharan Africa, the commonly used feeds are imported and accompanied by procurement challenges. Changing the larval feed abruptly without allowing the larvae to adapt to new brands of feed also leads to a decrease in mosquito colonies in the laboratory. We investigated locally acquired beans, maize, and dried herrings as alternate feeds for mosquito larvae reared under laboratory conditions. Four replicates for each treatment were prepared, each containing 100 first instar larvae of Anopheles gambiae Tiassalé mosquitoes. The larvae were introduced into 500 mL of dechlorinated tap water and maintained under standard environmental insectary conditions. The larvae were provided with 40 mg of the designated powdered feed—beans, maize, and herring fish—in single and combined treatments. Tetra® goldfish meal was included as a control. The larval mortality, developmental time, and number of pupae were recorded to evaluate the effectiveness of the feeds. Adult mosquitoes were weighed and measured to assess fitness, and females from each treatment were blood-fed and allowed to lay eggs to evaluate fertility. Larval survival differed significantly across diets (Kruskal–Wallis, p = 0.01), with maize-fed larvae showing the highest mortality (41.3%) and those with herring-based diets the lowest. Pupation and adult emergence were poorest in the maize and maize–bean groups, while the maize–herring combination achieved the highest emergence (92.6%, p = 0.03). Although overall differences were detected among the groups, conservative pairwise tests did not pinpoint specific group contrasts, but effect size estimates suggested biologically meaningful patterns. Generally, adult body weight and wing length did not differ by treatment except in maize-fed males (β = 0.371 mm, p = 0.022). Herring fish-based diets consistently supported larval survival, timely development, and robust fecundity, whereas maize-based diets were nutritionally inadequate. These findings highlight herring fish-based diets as a sustainable and cost-effective alternative to commercial feeds for maintaining Anopheles mosquito colonies, with potential to strengthen vector research capacity in resource-limited laboratories.