Comparative activity of three isolates of LdMNPV against two strains of Lymantria dispar

Abstract

Two newly identified geographic isolates of a nucleopolyhedrovirus (LdMNPV-H and LdMNPV-J) were evaluated against Disparvirus (LdMNPV-D), a baculovirus insecticide registered in Canada for the control of gypsy moth (Lymantria dispar (L.) (Lepidoptera: Lymantriidae)). Profiles of HindIII and EcoRI restriction enzyme digests of viral DNA from the three viral isolates are presented. Viral isolates were bioassayed using an inoculated diet plug method to determine the dose- and time-responses of second-instar larvae of both the European and Asian strains of gypsy moth. LdMNPV-D was found to be the most virulent isolate when tested against the European strain of gypsy moth, yielding an LD50 and an LD95 (estimates of the doses required to kill 50% and 95% of the test larvae, respectively) of 95 and 774 occlusion bodies (OBs), respectively. LdMNPV-H was the most virulent isolate when tested against the Asian strain, yielding an LD50 and an LD95 of 648 and 8540 OBs, respectively. Time-response data indicate that the three isolates differ little with respect to their speed of kill (ST50; estimate of the length of time required to kill 50% of the test insects) of either larval strain. These results indicate that both new isolates (LdMNPV-H and LdMNPV-J) should be investigated further for control of the Asian strain of the gypsy moth but not pursued for control of the European strain.

Comparison of the Activities of Three LdMNPV Isolates in the Laboratory Against the Chinese Strain of Asian Gypsy Moth

“…One of these two isolates, LdMNPV-H, was collected in Heilongjiang Province of China near Harbin (courtesy of Professor Yue Shukui, Northeastern Forestry University, Harbin). The other isolate, LdMNPV-J, was collected in Japan (Ibaraki Prefecture, Honshu Island; courtesy of Dr. Shimazu Mitsuaki, Forestry and Forest Products Research Institute) [16].…”

“…The eggs were reared at 25ºC, 60% RH, and 16L:8D photoperiod, i.e. the same conditions used in the first stage in Canada [16]. After hatching, 100 larvae were transferred to each of 150 cups (described above) containing a modified artificial gypsy moth diet [21,22] and reared at 25ºC, 60% RH, and 16L:8D photoperiod.…”

“…In addition, AGM and EGM can hybridize, and many of the resulting females can also fly [14,15]. The ability of both hybrid and purebred females to fly will likely allow the AGM to spread throughout North America much more rapidly than the European strain has so far, and cause more devastating economic losses [16]. Thus, the introduction of the Asian subspecies presents a far greater threat to the coniferous forests of Canada and the US than that posed by its European relative.…”

“…Russia, China, South Korea and Japan are four likely sources for these introductions because of increasing trade between Asia and North America. To prepare for the eventual potential establishment of the AGM in North America, three geographic isolates of LdMNPV were tested against laboratory colonies of the EGM and the AGM strain from Siberia, Russia (AGM-R) [16]. Restriction enzyme digestion profiles indicated that these three virus strains were similar yet distinct, and the isolates can be easily distinguished [16].…”

“…To prepare for the eventual potential establishment of the AGM in North America, three geographic isolates of LdMNPV were tested against laboratory colonies of the EGM and the AGM strain from Siberia, Russia (AGM-R) [16]. Restriction enzyme digestion profiles indicated that these three virus strains were similar yet distinct, and the isolates can be easily distinguished [16]. One of the three virus strains was isolated from the AGM from Heilongjiang (LdMNPV-H) Province, P.R.…”