Suppression of Aedes mosquito larvae using dragonfly larvae released into ovitraps (Diptera: Culicidae; Odonata: Libellulidae)

There has been a marked increase in the number of dengue cases reported in Japan. In 2014, 162 people contracted dengue fever from the virus transmitted by Aedes albopictus. The increased prevalence of the disease in Japan implies that climate change and globalization have accelerated the risk of dengue fever spreading to Japan. This study aimed to develop a method for using dragonflies as biocontrol agents for mosquito control. We conducted a field study to determine whether dragonfly larvae could suppress populations of A. albopictus larvae. Eighth instar larvae of Sympetrum frequens were released into an ovitrap in which they preyed upon mosquitos. Compared to the control treatment, mosquito larvae decreased significantly in ovitraps containing S. frequens and S. infuscatum (i.e., experimental treatment). The mean number of mosquito larvae remaining in S. frequens and S. infuscatum ovitraps was 1.5 +/- 4.6 (mean +/- SD) and 0.6 +/- 1.1, respectively. The results showed that S. frequens and S. infuscatum preyed on 410 to 710 and 339 to 592 mosquito larvae per ovitrap at each site. Based on estimates of the number of mosquito eggs laid in ovitraps during the field trial, S. frequens larvae consumed approximately 20.3 to 45.0 % of mosquito eggs in the ovitrap. Suppression effects of S. frequens and S. infuscatum lasted 41 +/- 13 and 35 +/- 13 days, respectively. The results obtained suggest that S. frequens in ovitraps is effective for regulating larval populations of mosquito vectors.