dc.description.abstract |
The insecticidal efficacy of indigenous isolate of entomopathogenic fungi Beauveria bassiana
(Balsamo) Vuillemin, Bacillus thuringiensis subsp. kurstaki (Dipel®) and a novel insecticide of
the class anthranilic diamide, chlorantraniliprole (Coragen®) was assessed in various laboratory
bioassays and in field trials against one of the major okra insect pest Earias vittella (Fab.) and
Earias insulana (Boisd.) (Lepidoptera: Noctuidae). Initially, the field population of Earias spp.
was monitored by their multiplication capacity in terms of fruit infestation and larval population
under different environmental regimes in five districts of Punjab, Pakistan. In laboratory
bioassays, second and fourth instar larvae of E. vittella, from three different populations were
exposed to the alone and combined applications of B. bassiana, B. thuringiensis and
chlorantraniliprole to investigate the effect of dose rate and insect population (strain) on the
insecticidal effectiveness of all three chemicals against the test insect species. The results of
current studies revealed that the maximum fruit infestation was observed in district Vehari
followed by Pakpattan, T.T. Singh, Faisalabad and Chiniot, however, the maximum fruit
infestation was recorded on the 5th week during both the years 2011 and 2012. The larval
population was maximum in Vehari followed by Pakpattan, T.T. Singh, Faisalabad and Chiniot
districts respectively, where the maximum larval population was observed in 5th week during both
the years 2011 and 2012. Generally, positive correlation has been observed between temperature,
larval population and fruit infestation, while negative correlation has been observed in case of
relative humidity, larval population and fruit infestation in both the years. In laboratory bioassays,
when B. bassiana was combined with B. thuringiensis, individually the B. thuringiensis was more
effective as compared with B. bassiana alone at all the three concentrations against both the larval
instars in all the three field populations. In combined treatments significant differences in larval
mortality were recorded with highest mortality at higher dose rate of B. bassiana and B.
thuringiensis. The combined action of B. bassiana and B. thuringiensis exhibited considerable
increase in larval mortality compared with their sole application. The population from Faisalabad
was most susceptible followed by T.T. Singh and Pakpattan. The maximum pupation was
observed at lower dose of B. bassiana and minimum in combined treatment at higher dose rate for
both the larval instars. Similar trend has been observed in case of adult emergence and egg
eclosion. When B. bassiana was combined with chlorantraniliprole, individually the
chlorantraniliprole was more effective compared with B. bassiana alone at all the three dose rates
against both the larval instars against all the three different populations. In combined treatments
significant differences in larval mortality were recorded with highest mortality at higher dose rate
of B. bassiana and chlorantraniliprole. The combined action of B. bassiana and
chlorantraniliprole exhibited considerable increase in larval mortality compared with their sole
applications. The Faisalabad population was most susceptible followed by T.T. Singh and
Pakpattan. Maximum pupation was observed at lower dose of B. bassiana and minimum in
combined treatment at higher dose rate for both the larval instars. Similar trend has been observed
in case of adult emergence and egg eclosion. During on farm trials higher larval population was
observed in B. bassiana treated plots and minimum in combined treatment of chlorantraniliprole
and B. thuringiensis for both the years 2012 and 2013, data regarding fruit infestation also
followed the same trend. The average number of Spiders, Bracon spp. and Trichograma spp. were
more after first spray compared with the second spray and significantly higher yield was recorded
in combined treatments as compared to the alone treatments with highest Cost-benefit ratio
(CBR). In both the growing year, CBR was maximum in plots treated with combined application
of Bt and Coragen. |
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