Pathology and properties of the tetravirus Helicoverpa armigera stunt virus

A quantitative study of the pathogenicity of Helicoverpa armigera stunt vir us (HaSV) (Tetraviridae) isolates toward larvae of several heliothine speci es was conducted along with studies on the stability of the virus to a vari ety of chemical, enzymic, and temperature treatments. Surface contamination bioassays of several HaSV isolates against H. armigera produced 50% effect ive concentration (EC50) estimates ranging between 568 and 9244 virus parti cles (vp)/mm(2). Against mid Ist instar larvae of H. armigera, H. punctiger a, and Heliothis punctifera, EC50 estimates for one isolate were 1288, 16,1 37, and 2667 vp/mm(2), respectively. The virulence of HaSV infection varied markedly with the age at which larvae were exposed to the virus. Presentat ion of the virus to the first three instars of H. armigera was accompanied by cessation of feeding, growth retardation, and eventual lethality, wherea s no adverse effects were observed when later instars were exposed to the v irus, even at very high concentrations. Active HaSV was recovered from fras s of larvae exposed to the virus as 1st instars. Household bleach (1% v/v; 0.04% w/v available chlorine, 0.004% w/v NaOH), formaldehyde (1% w/v), and temperatures greater than or equal to 65 degreesC completely inactivated Ha SV in suspension. Treatments with ether, proteinase K (1 mg/ml), H. armiger a gut contents, and temperatures between 22 and 55 degreesC partially inact ivated virus activity. No observable inactivation was observed after treatm ent with chloroform, chymotrypsin (1 mg/ml), trypsin (1 mg/ml), or RNase A (1 mg/ml). The virus was stable between pH 2.8 and pH 10.0 with around 60% loss of activity observed at pH 11.4. The pattern of pathogenic effects see n in several other insect species challenged by high concentrations of HaSV indicated that the host range of the virus is limited to species within th e lepidopteran family Noctuidae. The apparently restricted host range of Ha SV along with a number of other features indicate that this virus has consi derable potential for the development of novel control agents for use again st heliothine pests. (C) 2000 Academic Press.