Susana Raquel Cagnolo

Effect of storage temperature on survival and infectivity of Steinernema rarum (OLI strain) (Rhabditida: Steinernematidae)

Nematode strains of the entomopathogenic family Steinernematidae differ in their ability to infect insects at different temperatures. Survival and infectivity of infective juveniles (IJs) of Steinernema rarum (OLI) were studied after their storage at 23+/-2 degrees C and at 5+/-1 degrees C. Survival at 23+/-2 degrees C was always above 95%. At 5+/-1 degrees C, survival decreased at week 5, but infectivity did the same after week 2. Unlike other steinernematids, both infectivity and survival of IJs would be higher for S. rarum (OLI) when stored at 23+/-2 degrees C.

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.