Abstract
Third and fourth instar larvae of Aedes aegypti actively ingested entomopathogenic nematodes (EPNs) and their symbiotic bacteria, resulting in larval mortality. All six EPN species evaluated in this study were pathogenic to Ae. aegypti but varied significantly in their virulence. Heterorhabditis bacteriophora and Steinernema carpocapsae were most virulent, H. megidis and S. kraussei showed the least virulence, whereas H. downesi and S. feltiae had intermediate virulence. Larval mortality was dose dependent for all EPN species. When using a dose of 100 infective juveniles (IJs) per larva, H. bacteriophora and S. carpocapsae caused 90%-100% mortality, whereas H. downesi and S. feltiae caused only 40%-60% mortality. Even when using 200 IJs/larva, H. megidis and S. kraussei caused a maximum of 30%-40% mortality. Some of the invasive EPNs were melanized, suggesting a strong humoral defense response by the Aedes larvae. The degree of melanization was quite variable; some EPNs were totally enveloped in a melanin sheath while others were partially coated with melanin. Melanization did not stop the EPN from multiplying and killing the Aedes larvae. IJs released from infected larvae would have the potential to infect healthy mosquito larvae. Also, both bacterial supernatant and bacterial cell suspension of Xenorhabdus nematophila caused >91% larval mortality after 48 h, whereas only the bacterial cell suspension of Photorhabdus laumondii was effective against the mosquito larvae. These data provides useful information on the potential use of EPNs and/or formulated bacterial cell suspensions in the control of the important urban and container-breeding mosquito, Ae. aegypti, and are a starting point for future simulated and actual field studies.
Highlights
Aedes aegypti, a mosquito species that breeds in many natural and artificial aquatic sites in urban situations, is a major vector of several human diseases such as dengue fever, Chikungunya, and yellow fever (Rodriguez et al, 2007; WHO 2009)
H. bacteriophora caused the highest larval mortality (93%), and there was a significant difference between H. bacteriophora and other treatments except S. carpocapsae (F = 53.500; df = 6.35; p = 0.001) (Figure 1)
This study shows that older (3rd and 4th) Ae. aegypti larvae will readily ingest entomopathogenic nematodes (EPNs), which leads to their death
Summary
A mosquito species that breeds in many natural and artificial aquatic sites in urban situations, is a major vector of several human diseases such as dengue fever, Chikungunya, and yellow fever (Rodriguez et al, 2007; WHO 2009). Yellow fever has been reasonably brought under control through its vaccine (Monath, 2005), no vaccine is available against dengue (Guzman, 2005; MacKenzie et al, 2004), which causes around 100 million infections (a 4-fold increase since 1990), 0.5 million cases of dengue hemorrhagic fever globally affecting 195 countries, and at least 40,000 deaths annually (Gubler, 2002; Zheng et al, 2021) Several factors such as unprecedented population growth (primarily in urban centres of tropical countries), the increased movement of viruses in infected humans. These factors, together with the concerns of risks to human health and increased environmental pollution caused by the synthetic insecticides, have prompted the search for safer alternative control strategies
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