Developmental Rate Of The Endo-Developmental, Stages Of Micropljtls ruf1ventrts Kok. In Viral Inoculated Larvae Of Spodoptera littoralis (Boisd.)

• E.M. Hegazi1, L.M.Z. Abo Abd-AlIah2, S.M. Abul Ella3 and O.A. Khamiss4
• ¹ Faculty of Agriculture, El-Shatby, Alexandria University.
• ² Plant Protection Research Institute Sabahia, Alexandria.
• ³ Faculty of Agriculture, Cairo University.
• ⁴ Generic Engineering Institute, Menoufyia University.

Abstract

The effects of subletbal concentrations of nuclear polyhydrosis virus (SINPV) and granulosis virus (SIGV) on the endo-developmental stages of the parasitoid, Microplitis rufiventris Kok. were studied by feeding the cotton leafworm, Spodoptera littoralis (Boisd.) larvae on viral inoculated diet. The effect of SINPV (2.78 x 10⁷ PIB/ml) on the developmental rate and sensitivity of the parasitoid larvae varied according to application time and parasitoid age. Significant adverse effect on the parasitoid development was detected when the hosts were treated 24 h prior or simultaneously with parasitization compared to those in hosts treated 2 or 6 days later. The egg stage and older parasitoid larvae were more tolerant to S1NPV infection than the 1st instar larvae. The SIGV infection was only initiated 48 h prior parasitization. SIGV-treatment (11.9 OD) significantly (P<0.01) prolonged the duration of the 1^st instar parasitoid larvae compared to those in healthy parasitized hosts. The medium concentration of SIGV (11.9 OD) was more effective in disrupting the development of young parasitoid larvae than higher one (119 OD). However, in both treatments of SIGV, the parasitoid developmental scores of parasitoid larvae were significantly (P<0.01) lower than in control. Generally, the SIGV-infected hosts were still alive after the control had been killed by emergence of the parasitoid. In all treatments with either S1NPV or SIGV, the parasitoid larvae suffered from prolongation of larval duration, partially molted cuticle, deformed development, and aggregation of host materials with melanin deposition on the surface of parasitoid larvae. Also, the developmental scores of parasitoid larvae in virus-infected hosts were significantly lower than control. The study showed that oviposition by the parasitoid should preceding exposure to a lethal concentration of the entomopathogenic virus by 5 or 6 days at normal field conditions to ensure survival of a substantial proportion of the parasitoid population. Also, Microplitis rearing can greatly get benefit by utilizing virus-free Spodoptera larvae and food free from contamination