larvae were resistant to the infection and there was an inverse relationship between
mortality and larval weight. In another study, the pathogenicity of other viral isolates
was surveyed on the second instar larvae of H. armigera. Then, LC 50 and LD 50
values, and yield parameters (yield/larva and productivity ratio) of seven geographic
isolates of H. armigera NPV were evaluated under laboratory conditions (Mehrvar
et al. 2008a). The LC 50 of seven isolates of NPV including NGM, OTY, PRB, CBE,
RHI, MUM and HYD against second instar larvae of H. armigera was determined.
The highest pathogenicity was observed in the NGM isolate with 0.028 OB/mm
2
which was more virulent than HYD by a factor of 2.75. Also, the LT 50 of NGM was
the lowest among the isolates by 97.8 h.
A few isolates of HearNPV have been collected from tomato fields of the East
Azerbaijan province (Mehrvar 2013). Subsequently, a study was designed to evaluate the age-dependent resistance of H. armigera larvae against two native virus
isolates (EAZ-I and EAZ-II) and a non-native isolate (STD) (Mehrvar 2015a).
Results showed that larval resistance to virus isolates increases with larval age. It
was shown that the age and weight of the larva as well as ambient temperature had
meaningful effects on the larval mortality and the virus replication inside the larva.
The optimum larval stage and ambient temperature for HearNPV in vivo production
were the early fifth instar larvae and 25
C, respectively (Mehrvar 2015b). The STD
isolate in early second instar larvae had the lowest LC 50 value (1.82 Â 10
2 OB/ml)
and the EAZ-II isolate in fifth instar larvae had the highest LC 50 value (1.43 Â 10
6
OB/ml) (Mehrvar 2015b).
Among the entomopathogens, HearNPV is highly virulent in its host. The main
limiting factor for application is the required time to kill the insect, which takes at
least 3–5 days. Mehrvar (2015a), collected LC 50 data for a non-native isolate (STD)
of HearNPV and two native isolates (EAZ-I and EAZ-II) from the East Azarbaijan
province in 2010. All isolates showed a high rate of virulence against the second
instar larvae of H. armigera. The STD isolate had the lowest LC 50 value (7.27 Â 10
2
OB/ml) and the shortest LT 50 (97.8 h). EAZ-I and EAZ-II isolates had lower
virulence than STD. For fifth instar larvae, the results were similar. When EAZ-II
was combined with flufenoxuron, a chitin synthesis inhibitor, the lowest LC 50 value
calculated was 1.83 Â 10
4 OB/ml. The LT 50 data showed that flufenoxuron combined with native virus isolates of EAZ-I and EAZ-II, increased speed mortality rate
by 19.88 and 19 percent, respectively. Flufenoxuron could effectively enhance
virulence by affecting the chitin contents of peritrophic membrane (Mehrvar 2015a).
According to Pour Mirza (1998), efficiency of a viral insecticide is related to
various factors such as commune period and larval weight. The necessary time for
larval mortality is related to the time required for the virus to proliferate until it
reaches a deadly level (Pour Mirza 1998). He bioassayed an isolate of NPV on
Heliothis viriplaca (Hufnagel 1766) (Lep.: Noctuidae). The results demonstrated
that the older larvae have a higher LT 50 . Therefore, one disadvantage of viral
insecticides is the long interval between the initial infection and the host’s death.
These studies, although limited, show that there are isolates of HearNPV with
potential for application against H. armigera in Iran which require additional
510
M. Mehrabadi et al.
mortality and larval weight. In another study, the pathogenicity of other viral isolates
was surveyed on the second instar larvae of H. armigera. Then, LC 50 and LD 50
values, and yield parameters (yield/larva and productivity ratio) of seven geographic
isolates of H. armigera NPV were evaluated under laboratory conditions (Mehrvar
et al. 2008a). The LC 50 of seven isolates of NPV including NGM, OTY, PRB, CBE,
RHI, MUM and HYD against second instar larvae of H. armigera was determined.
The highest pathogenicity was observed in the NGM isolate with 0.028 OB/mm
2
which was more virulent than HYD by a factor of 2.75. Also, the LT 50 of NGM was
the lowest among the isolates by 97.8 h.
A few isolates of HearNPV have been collected from tomato fields of the East
Azerbaijan province (Mehrvar 2013). Subsequently, a study was designed to evaluate the age-dependent resistance of H. armigera larvae against two native virus
isolates (EAZ-I and EAZ-II) and a non-native isolate (STD) (Mehrvar 2015a).
Results showed that larval resistance to virus isolates increases with larval age. It
was shown that the age and weight of the larva as well as ambient temperature had
meaningful effects on the larval mortality and the virus replication inside the larva.
The optimum larval stage and ambient temperature for HearNPV in vivo production
were the early fifth instar larvae and 25
C, respectively (Mehrvar 2015b). The STD
isolate in early second instar larvae had the lowest LC 50 value (1.82 Â 10
2 OB/ml)
and the EAZ-II isolate in fifth instar larvae had the highest LC 50 value (1.43 Â 10
6
OB/ml) (Mehrvar 2015b).
Among the entomopathogens, HearNPV is highly virulent in its host. The main
limiting factor for application is the required time to kill the insect, which takes at
least 3–5 days. Mehrvar (2015a), collected LC 50 data for a non-native isolate (STD)
of HearNPV and two native isolates (EAZ-I and EAZ-II) from the East Azarbaijan
province in 2010. All isolates showed a high rate of virulence against the second
instar larvae of H. armigera. The STD isolate had the lowest LC 50 value (7.27 Â 10
2
OB/ml) and the shortest LT 50 (97.8 h). EAZ-I and EAZ-II isolates had lower
virulence than STD. For fifth instar larvae, the results were similar. When EAZ-II
was combined with flufenoxuron, a chitin synthesis inhibitor, the lowest LC 50 value
calculated was 1.83 Â 10
4 OB/ml. The LT 50 data showed that flufenoxuron combined with native virus isolates of EAZ-I and EAZ-II, increased speed mortality rate
by 19.88 and 19 percent, respectively. Flufenoxuron could effectively enhance
virulence by affecting the chitin contents of peritrophic membrane (Mehrvar 2015a).
According to Pour Mirza (1998), efficiency of a viral insecticide is related to
various factors such as commune period and larval weight. The necessary time for
larval mortality is related to the time required for the virus to proliferate until it
reaches a deadly level (Pour Mirza 1998). He bioassayed an isolate of NPV on
Heliothis viriplaca (Hufnagel 1766) (Lep.: Noctuidae). The results demonstrated
that the older larvae have a higher LT 50 . Therefore, one disadvantage of viral
insecticides is the long interval between the initial infection and the host’s death.
These studies, although limited, show that there are isolates of HearNPV with
potential for application against H. armigera in Iran which require additional
510
M. Mehrabadi et al.