The field experiment was conducted during 2013-16 at Navsari Agricultural University, Paria, Gujarat to study the role of weather parameters on population dynamics of oriental fruit fly, Bactrocera dorsalis on mango, Mangifera indica L. Fruit flies were recorded throughout the investigation period, wherein maximum catches were observed during April - July which coincided with fruiting and harvesting stages of the crop. Weather parameters viz., minimum temperature, evening relative humidity, rainfall and wind velocity were found to be important predictors of fruit fly catches, while maximum temperature and morning relative humidity failed to establish significant correlation with the catches. The optimized model developed using rainfall and wind velocity predicted fruit fly catches based on R2 value to the tune of 78 per cent. This forewarning model may help mango farmers to take advance decision for minimizing the quantitative and qualitative crop losses caused by fruit flies of the region.
The influence of environmental parameters on the development of powdery mildew caused by Oidium mangiferae Berthet on mango inflorescence was studied for seven consecutive years (2012-18) in humid tropics climatic conditions of South Gujarat. The disease incidence and severity (DIS), area under disease progress curve-AUDPC (A-value) and apparent infection rate (r-value) were recorded at panicle and fruit setting stages of the tree at weekly intervals. The correlation studies showed that incidence and severity of powdery mildew significantly negative relationship with morning relative humidity (r = -0.631; p<0.05 and r = -0.721; p<0.01) and average relative humidity (r = -0.766 and r = -0.787; p<0.01). Temperature (maximum and average) and evaporation showed positive relationship with incidence and severity of powdery mildew. Further, stepwise linear regression model indicated that average relative humidity as single predictor independent variable had the strongest relationship disease incidence and severity, which explained 59 percent disease incidence and 62 percent for disease severity variability. This forewarning model can be useful for efficient management of powdery mildew disease of mango and as well as agro advisory services to farmers.
The incidence of egg and larval parasitoids of Chilo partellus was monitored in insecticide free maize fields at the Indian Agricultural Research Institute, New Delhi, for three Kharif seasons of 2013 to 2015. The hymenopteran parasitoid, Trichogramma sp. was recorded to be the only egg parasitoid in this area, while a good number of larvae were parasitized by braconid, Cotesia flavipes. The egg parasitism was recorded on the freshly laid eggs of stem borer obtained by artificially releasing the adults of C. partellus on maize cultivars, HQPM1 and PMH1, at 12 days after germination. There was no egg parasitism recorded during Kharif 2013 and 2014, whereas 5.6 percent egg-mass parasitism by Trichogramma sp. was recorded during Kharif, 2015. The larval parasitoids were monitored by artificially infesting the maize plants with neonates of laboratory reared C. partellus. The larvae were allowed to develop on maize plants under field conditions for 20 days. The plants showing stem borer damage were cut and brought to the laboratory. The larvae collected from infested maize plants were reared in the laboratory. The maggots of C. flavipes recovered from parasitized larvae ranged from 29-100, 41-50 and 20-80 percent during Kharif 2013, 2014 and 2015, respectively. The result of this study indicated that parasitism by Cotesia was influenced by age of plants damaged by C. partellus. The young maize plants seemed to be more attractive to the foraging of Cotesia and more stem borer larvae were parasitized on these plants as the maximum (58 percent) parasitism was observed at 40-day-old crop. The parasitoid was found to be active on maize from 40-60 days after germination and the incidence decreased thereafter. Insecticides should not be used during this period. The current studies also revealed that host densities had no significant effect on percentage parasitism by Cotesia.
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