Trabajo Científico Article ISSN 0373-5680 (impresa), ISSN 1851-7471 (en línea) Revista de la Sociedad Entomológica Argentina 73 (3-4): 99-108, 2014 Susceptibility of larvae of Aedes aegypti (Linnaeus) (Diptera: Culicidae) to entomopathogenic nematode Heterorhabditis bacteriophora (Poinar) (Rhabditida: Heterorhabditidae) PESCHIUTTA, María L.1, 2, Susana R. CAGNOLO2 & Walter R. ALMIRÓN2, 3 1 Grupo de Estudios Biofísicos y Ecofisiológicos (GEBEF), Universidad Nacional de la Patago- nia San Juan Bosco, Km 4 S/N Ciudad Universitaria (9000) Comodoro Rivadavia, Argentina. E-mail: [email protected] 2 Cátedra de Parasitología, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Av. Vélez Sársfield 299 (5000) Córdoba, Argentina. 3 Centro de Investigaciones Entomológicas de Córdoba, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Av. Vélez Sársfield 1611 (5016) Córdoba, Argentina. Susceptibilidad de larvas de Aedes aegypti (Linnaeus) (Diptera: Culicidae) al nematodo entomopatógeno Heterorhabditis bacteriophora (Poinar) (Rhabditi- da: Heterorhabditidae) RESUMEN. Aedes aegypti (Linnaeus) (Diptera: Culicidae) es vector de los agentes etiológicos de la fiebre amarilla y del dengue. Una alternativa al control químico de este vector es el uso de agentes biológicos. Los nematodos entomopatógenos son efectivos en el control de plagas. La infectividad y el ciclo de vida de un aislado argentino de Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) en larvas de A. aegypti se registró por primera vez bajo condiciones de laborato- rio. Para cada unidad experimental, 30 larvas de mosquito de segundo estadio fueron expuestas a 8 dosis del nematodo (0:1, 1:1, 5:1, 15:1, 100:1, 500:1, 750:1, 1500:1). Los juveniles infectivos (JIs) utilizados fueron multiplicados sobre Galleria mellonella (Lepidoptera: Pyralidae). La continuidad infectiva de los JIs obtenidos de A. aegypti fue probada aplicándolos en una dosis de 100:1 sobre larvas del mosquito. Las tasas de mortalidad fueron de 0% a 84%. El número de nematodos desarrollados dentro de la larva de mosquito, la mortalidad larval y los nuevos JIs se incrementaron con el aumento de la dosis de nematodos. Los resultados indican que H. bacteriophora es capaz de infectar larvas de A. aegypti, se desarrolla y produce nuevos JIs, permitiendo la continuidad de su ciclo de vida. PALABRAS CLAVE. Heterorhabditis. Ciclo biológico. Mosquitos. Infectividad. Con- trol biológico. ABSTRACT. Aedes aegypti (Linnaeus) (Diptera: Culicidae) is a vector of etiological agents of yellow fever and dengue. An alternative to chemical control of this vector is the use of biological agents. Entomopathogenic nematodes are effective in pest control. The infectivity and life cycle of an Argentinean isolate of Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) on Aedes aegypti larvae is registered for the first time under laboratory conditions. For each experimental unit, 30 second-instar larvae were exposed to 8 nematode doses (0:1, 1:1, 5:1, 15:1, 100:1, 500:1, 750:1, 1500:1). The infective juveniles (IJs) used were multiplied on Galleria mellonella (Lepidoptera: Pyralidae). The infective continuity of IJs obtained from A. aegypti was tested applying the nematodes in a 100:1 dose on mosquito larvae. Larval mortality rates ranged from 0% to 84%. The larval mortality, the num- Recibido: 13-III-2014; aceptado: 10-VII-2014 99 Revista de la Sociedad Entomológica Argentina 73 (3-4): 99-108, 2014 ber of nematodes developed inside mosquito larvae and the number of new IJs increased with the increase of the nematodes dose. The results indicated that H. bacteriophora is able to infect A. aegypti larvae, and these nematodes can develop and produce new IJs, allowing the continuity of its life cycle. KEY WORDS. Heterorhabditis. Biological cycle. Mosquitoes. Infectivity. Biological control. INTRODUCTION Cagnolo & Almirón, 2010). Recent assays have found that H. bacteriophora (Poinar) kills Culex Aedes aegypti (Linnaeus) (Diptera: Culici- quinquefasciatus mosquitoes faster and in a dae) is the most important vector for the trans- more effective way than other Heterorhabditis mission of etiological agents of yellow fever, and Steinernema species (Zohdy et al., 2013). dengue and dengue hemorrhagic fever (DHF) The infectivity, reproduction and size of in America (Nelson, 1986; Salvatella-Agrelo, progeny of EPNs may be related to nematode 1996; Simmons et al., 2012). The historic di- behavior, adaptation to a given host (ability rection of Aedes mosquito dispersion in South to overcome the defense mechanism of host) America has been towards higher latitudes (Kaya, 1990) and different developmental stag- and from tropical to sub-tropical areas, in par- es and size of the host (Murdoch et al., 1997; ticular in the Southern Region. Nowadays, the Morgan & Hare, 1997; Boff et al., 2000). Stein- current geographical distribution of A. aegypti ernematids and heterorhabditids are terrestrial in Argentina has been expanded (Rossi et al., organisms that move in the interstitial water be- 2006; Díaz-Nieto et al., 2013). Insecticides are tween the soil particles (Begley, 1990; Cagnolo used in the reduction of larval and adult A. ae- & Almirón 2010). However, the aquatic habitat gypti populations; however, the control success offers an excellent environment for nematode is limited by resistance to chemical products survival (Pandii et al., 2010). Cagnolo & Almirón (Georghiou et al., 1987; Mekuria et al., 1991; (2010) demonstrated than IJs: (infective juve- Seccacini et al., 2008; Bisset-Lazcano et al., niles) can swim actively looking for the mosqui- 2009). Alternative control strategies were imple- to larvae. Moreover, mosquito larva movement mented such as biological agents, environmen- favors the suspension of IJs into the water. Par- tal management and the use of insecticides of ticularly, A. aegypti larvae collect detritus from biological origin, providing modes of innovative the aquatic substratum and this feeding behav- action and reducing the risk of cross resistance ior leave the insects more exposed to nema- (Pérez-Pacheco et al., 1998; Parra et al., 2007). todes than other mosquito species (Pandii et Currently, several assays were carried out us- al., 2010). This could make A. aegypti larvae ing, for instance, mermithid nematodes against easy targets for control with EPNs. A. aegypti and other mosquito larvae (San- Heterorhabditid nematodes are symbiotically tamarina-Mijares, 1994; Santamarina-Mijares associated with the bacterium Photorhabdus lu- et al., 2000; Achinelly et al., 2004, Achinelly & minescens (Boemare et al., 1993). Bacteria are Micieli, 2013; Sanad et al., 2013). Furthermore, transmitted into the haemocoel of the host insects entomopathogenic nematodes (EPNs) of the by a developmentally-arrested third juvenile stage, genera Steinernema (Steinernematidae) and the infective juvenile. Reaching the host haemo- Heterorhabditis (Heterorhabditidae) provide an coel, the IJs initiate the development and release environmentally safe and economically reason- of their symbiotic bacteria (Smart, 1995; Toledo et able alternative against a variety of important al., 2006). The host dies within 48 hours after infec- insect pests and some of them could be used tion (García del Pino, 1994; Smart, 1995), although commercially for biocontrol (Ehlers, 1996; Cag- sometimes, it can continue its development for a nolo et al., 2010; Mbata & Shapiro-Ilan, 2010; while, causing the melanization of the nematode Yan et al., 2013; Zadji et al., 2013). However, few as a defensive reaction (Poinar & Kaul, 1982). studies were developed to demonstrate effec- There is no research done until today describ- tiveness of EPNs against mosquitoes (but see ing the life cycle of the genus Heterorhabditis in Poinar & Kaul, 1982; Molta & Hominick, 1989; A. aegypti. This information is fundamental to un- 100 PESCHIUTTA, M. L. et al. Susceptibility of Aedes aegypti larvae to Heterorhabditis bacteriophora derstand their persistence, reproductive poten- as an energy source (Smart, 1995; Burnell & tial and effect on insect host populations, and to Stock, 2000). Before the assays, viability was develop predictive models for control programs confirmed by observing nematode activity (Ricci et al., 1996; Oğuzoğlu Ünlü & Özer, 2003). (rapid wiggling) under a binocular microscope A comprehensive knowledge of the life cycle of (Laznik et al., 2010). the nematode and the reproduction potential in mosquitoes is needed as a prerequisite for ge- Infectivity of H. bacteriophora on A. ae- netic studies aimed at enhancing the nematode gypti larvae performance under field conditions (Zioni et al., Infection experiments were carried out using 1992). Our study was performed in order to eval- cohorts of 30 second-instar larvae put in plastic uate the infectivity and life cycle of Heterorhabdi- trays (10.5 x 12 x 4 cm), containing 80 ml of water tis bacteriophora on A. aegypti larvae. and maintained at 26 ºC. The concentration of the IJs used in these experiments ranged from 0 to MATERIALS AND METHODS 45000 IJs per tray (i.e. parasite: host ratios of 0:1 (control), 1:1, 5:1; 15:1, 100:1, 500:1, 750:1 and Mass rearing of mosquitoes and nematodes 1500:1). The culture flasks with stored IJs were Aedes aegypti larvae and nematodes used diluted to a final volume of 250 ml with sterile wa- in the experiment were obtained from colonies ter. An estimation of the number of IJs present in maintained at