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Three specific DNA probes were used for the detection of the nuclear polyhedrosis (NPV) virus of Lymantria dispar (LdNPV) genome. Two of these probes, H2 and H3 were obtained by classical cloning method and one (TR6) by polymerase chain reaction (PCR). These probes, used individually or in a pool in the standard slot–blot hybridizations, were able to detect 109 genome copies. By performing 35 cycles of PCR amplification before hybridization with primers specific to LdNPV genome on DNA extracted from infected larvae, the sensitivity of the hybridization technique was increased, so that as little as 10 copies of the LdNPV genome could be detected. Using these methods, L. dispar naturally infected by LdNPV were identified among field populations in Canada and in the United States near the eastern Canadian border. Using a combination of PCR and hybridization, LdNPV contamination of egg masses were also detected. By disinfecting the eggs with sodium hypochlorite prior to PCR amplification and hybridization, it was also demonstrated that transmission of viral infection in the natural populations is mainly caused by external contamination of the egg and is unlikely to occur through the transovarial route.

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RésuméUn inventaire de trois années (1972 à 1974) effectué à 178 stations réparties dans le Québec méridional a révélé la présence de 30 espèces de culicides. Pour deux de ces espèces (Aedes decticus et C. melanura) il s’agit d’une extension d’aire. Les types de gites larvaires où ces deux espèces ont été trouvées sont présentés et caractérisés par la végétation.