Authors: FAROOQ A. SHAH, MOSTAFA M. ABDOARRAHEM, COLIN BERRY, MUSTAPHA TOURAY, SELÇUK HAZIR, TARIQ M. BUTT

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.

Keywords: Entomopathogenic nematode (EPN) ingestion, Aedes aegypti, symbiotic bacteria, H. bacteriophora, S. carpocapsae

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