Abstract:

To explore the mechanism of a fluorescent brightener, Tinopal LPW, in enhancing infection of LdNPV and the effect of host plants and LdNPV geographic stains on Phenoloxidase in gypsy moths, the 5^th instar larvae of gypsy moth, which are pests of Populus cathayana, Larix principis-rupprechtii and Aarmeniaca sibirica were treated with 3 virus strains (LdNPV-D, LdNPV-H, LdNPV-J) and their mixture with Tinopal LPW with and without Tinopal LPW, respectively. Incubation with distilled water or Tinopal LPW only served as controls. As a result, there were 6 treatments and 2 controls. Phenoloxidase (PO) activity in haemolymph of larvae was measured at 12, 24, 48, 72 and 96 h after the treatments. The experiment (30 larvae per treatment) was replicated three times. The results showed that effects of host plants, virus strain and the brightener on the PO activity in the 5^th instar gypsy moth larvae were significant. PO activity increased after the larva were infected by pure virus 12 h later, and then decreased after 24 h comparing with both distilled water and Tinopal LPW controls. The effect of D-strain, H-strain and J-strain with addition of Tinopal LPW on the phenoloxidase activity of gypsy moth was dependent on the host plants. Larvae fed on A. sibirica, the PO activity was lower than that in larvae treated with virus strains without the brightener, as well as both controls. Larvae fed on poplar or larch, the PO activity in larvae treated with D-strain, or H-strain with the brightener was lower than that in larvae treated with the two stains only, or controls, but there was no difference in Po activity in larvae treated with J-strain between with and without Tinopal LPW addition. Tinopal LPW significantly reduced the PO activity in comparison with distilled water.

Key words: gypsy moth, LdNPV, phenoloxidase, optical brightener, host plant