Biological control of the potato tuber moth (Phthorimaea operculella Zeller) in the Republic of Yemen using granulosis virus: Propagation and effectiveness of the virus in field trials

A granulosis virus (PoGV) infecting the potato tuber moth, Phthorimaea operculella, in the Republic of Yemen was evaluated for its use in an inundative approach to control this pest. In field trials on potatoes, the effectiveness of the virus was examined on-farm and on-station using an unpurified preparation (PoGV I) and a purified glycerine-formulated virus preparation (PoGV II). The virus infection and mortality of potato tuber moth larvae were dependent on the virus concentration applied. After application 5x10(12) occlusion bodies (OB) ha(-1) of PoGV I, the proportion of virus-infected larvae increased, fluctuating between 26 and 39% 14-35 days after treatment. At a granulosis virus concentration of 5x10(13) OB ha(-1), clear symptoms of granulosis virus infection (milky white coloration and reduced vitality) were observed in larvae collected 11 days after treatment. A total of 70% of the fourth instar larvae collected 19 days after treatment with PoGV I were infected. Further observations revealed very high rates of effectiveness in terms of larval mortality. The preparations PoGV I and poGV II were not found to differ in their degree of effectiveness, which resulted in a mortality of potato tuber moth larvae of 85.3% for PoGV I and 82.5% for PoGV II respectively.