Submitted to: Book Chapter
Publication Type: Book / chapter
Publication Acceptance Date: 4/15/2008
Publication Date: 4/1/2009
Citation: Mcintosh, A.H., Grasela, J.J. 2009. Early Detection of Baculovirus Expression and Infection in Lepidopteran Larvae Fed Occlusion Bodies of an AcMNPV Recombinant Carrying a Red Fluorescent Protein Gene. In: Halley, G.T., Fridian, Y.T., editors. Environmental Impact Assessments. Hauppauge, NY: Nova Science Publications. p. 457-467. Interpretive Summary: Baculoviruses are the viral agents of choice for the control of many insect pests that attack forest, field and vegetable crops. While these viruses have been successful in controlling many of these pests they suffer from several disadvantages. The present study addresses one of such short comings, namely the early determination of virus presence in caterpillars following feeding on treated crops. Unlike chemical insecticides which act very rapidly against these pests, viruses take several days before the hosts displays typical symptoms of infection and during this period further damage could be done to the crops in question. In the present study we employed a baculovirus carrying a fluorescent marker which is expressed early after the virus is consumed and can be readily detected under ultraviolet light microscopy. Our results showed that virus expression was detected as early as 16 hours following intake of the virus which resulted in the eventual death of the insect. Even less susceptible caterpillars displayed presence of the virus as early as 48 hours post feeding. This finding should be very useful and applicable under field conditions in predicting infection of caterpillars exposed to viruses employed as biological control agents.
Technical Abstract: A method has been devised utilizing a baculovirus recombinant (AcMNPV hsp70Red) carrying a red fluorescent protein (RFP) gene under the early heat shock promoter (hsp70) to assess potential infectivity of larvae fed occlusion bodies. A time study was employed whereby first and third instars of Trichoplusia ni, Heliothis subflexa and Helicoverpa zea could be followed for red fluorescence under a UV-light inverted microscope at various time intervals following diet surface feeding of occlusion bodies. Larvae of T. ni and H. subflexa that are permissive to AcMNPV showed 100% fluorescence by 24h and 36h respectively for 1st instars exposed to 1 x 105 OB. Even when the concentration of OB was reduced 100 fold to 1 x 103 OB, 94-100% fluorescence was observed by 24h post feeding. H. zea which is less permissive to AcMNPV than T. ni and H. subflexa and when 1st instars were fed 1 x 105 OB showed 100% red fluorescence at 48h post exposure as contrasted with 86-90% fluorescence at the 96h exposure period for the lower dose of 1 x 103 OB. T. ni and H. subflexa third instars fed 1 x 105 OB gave 100% fluorescence between 24-36h post exposure whereas at the lower dose of 1 x 103 OB 100% fluorescence was achieved between 48-72h post exposure. All larvae of each species that gave 100% fluorescence resulted in 100% mortality.