M. A. Bertolotti

Ensayos de susceptibilidad de larvas de Aedes aegypti y Culex quinquefasciatus al nematodo entomopatógeno Heterorhabditis bacteriophora, en laboratorio

INTRODUCTION Aedes aegypti is the vector of dengue, yellow fever, Zika and Chikungunya viruses, and Culex quinquefasciatus is the vector of St. Louis and West Nile encephalitis viruses. OBJECTIVE To evaluate infectivity of Heterorhabditis bacteriophora N4 in C. quinquefasciatus and A. aegypti larvae under laboratory conditions. MATERIALS AND METHODS Thirty second-instar larvae of the two mosquito species were exposed each to different doses (0:1, 1:1, 5:1, 15:1, 100:1, 500:1, 750:1 and 1,500:1) of nematode infective juveniles. Four replications per dose were performed. RESULTS Parasitism varied between 2.5 and 80 % in C. quinquefasciatus, and between 4.2 and 92.5 % in A. aegypti, with significant differences between doses (p<0.0001). DL50 were: 160.8 infective juveniles per larva for C. quinquefasciatus and 113.6 infective juveniles per larva for A. aegypti. In C. quinquefasciatus, 4 to 6 % of the infective juveniles developed to adults and in A. aegypti, 12- 61 %. In A. aegypti the emergence of new infective juveniles occurred with 100:1, 500:1, 750:1 and 1,500:1 infective juveniles per larva, and in C. quinquefasciatus, with 1,500:1 infective juveniles per larva. Melanization of infective juveniles was observed in both mosquito species. CONCLUSION The susceptibility of these mosquito species to parasitism of an indigenous isolate of H. bacteriophora in the laboratory was demonstrated. Heterorhabditis bacteriophora N4 could be an efficient biological control agent.

New findings of Heterorhabditis bacteriophora and Steinernema rarum (Nematoda: Heterorhabditidae, Steinernematidae) in Córdoba, Argentina

A total of 152 soil samples collected from gardens of private properties at Cordoba city, Argentina, were evaluated for the presence of entomopathogenic nematodes (EPNs) . The insect bait method was used to isolate EPNs. The nematodes were characterized using both classic (morphometric characters) and molecular methods (analysis of internal transcribed spacer (ITS) and D2/D3 sequences of 28S genes). The recovery frequency of EPNs was 10.53%. Isolates belonging to the genera Heterorhabditis Poinar, 1976 and Steinernema (Travassos, 1927) were detected. Two isolates were identified as Steinernema rarum and four as Heterorhabditis bacteriophora . Granulometry, relative humidity and pH of the soil were determined and no significant differences were found among sites with presence or absence of EPNs when edaphic characteristics of sites were compared. The occurrence of EPNs in home gardens was determined for the first time, expanding S. rarum and H. bacteriophora currently known geographical distribution and increasing the diversity of populations of these nematodes to use against insect pests of urban areas.

Analysis of two isolates of a Heterorhabditis bacteriophora population detected in Córdoba, Argentina

Entomopathogenic nematodes of the genus Heterorhabditis are associated with symbiotic bacteria Photorhabdus spp. (Enterobacteriaceae). Taxonomic studies confirm that each species of nematode has a specific natural association with only one species of bacterium (Boemare & Doucet, 1996). Except in a few cases, the bacteria change the colour of the parasitized insect to different reddish tones and produce bioluminescence (Grimont et al., 1984; Boemare & Doucet, 1996). These distinct colours would be assumed to be due to the different species of Photorhabdus and, consequently, to indicate different species of Heterorhabditis. Therefore, the colour of the cadaver has been used as a taxonomic character (Stock, 1993). In a single soil sample from Cordoba City, Argentina, two isolates of Heterorhabditis were found that were clearly distinguished by the colour of the parasitized Galleria mellonella larva: isolate A, violet-brown; B, reddish. These different phenotypes led us to suppose that the nematode isolates were associated with different symbiotic bacteria and that the nematodes were different species. The purposes of this work were: to establish the identity of the isolates and to compare them on the basis of morphological and morphometric characters, and isozyme patterns.