SPATIO-TEMPORAL PATTERNS AND BIO-RATIONAL MANAGEMENT OF EARIAS SPP. ON OKRA (ABELMOSCHUS ESCULENTUS L. MOENCH)

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.