Assessment of Pest Severity and Biological Parameters of Bactrocera minax in Sweet Orange Orchards in Central Nepal

Abstract

Chinese Citrus fly, Bactrocera(Tetradacus) minax(Enderlein), univoltine fruit fly species, is a serious insect pest in Nepal, Bhutan, China, India causing 100% fruit drop in sweet orange (Citrus sinensis L.) orchards in severe case. Four elevation ranges: 1400-1474masl, 1475-1549masl, 1550-1624masl and >1624masl of Ramechhap district were taken for the study of severity of infestation by this fly species in November 2018. A subsequent rearing was conducted at Agriculture and Forestry University, Chitwan, Nepal upto April 2019 to assess various developmental parameters of Bactrocera minax starting from larval stage in infested sweet oranges to the adult flies. Elevation range had the most significant effect (P<0.05) on pest severity (2017/18). Pest severity had strong relationship on elevation of orchards (R2=0.6638). Maximum pest severity (37.12%) was found in 1550-1624masl and minimum (2.90%) in 1400-1474masl. Maximum mean maggots/fruit (6.40±1.25) at 1550-1624masl and minimum (3.95±0.92) at 1475-1549masl were recorded. Post-pupal mortality was higher than pre-pupal mortality. Maximum pre-pupal mortality (11.13±5.24%) at >1624masl and the minimum (2.08±1.46%) at 1550-1624masl were recorded while 1475-1549masl and 1400-1474masl had the respective minimum (25.81±7.59%) and maximum (36.08±9.17%) post-pupal mortality. Most adult flies emerged by 2nd week of March lasting 115 days for adult eclosion. Sex ratio (male: female) was maximum (2.5) at 1400-1474masl and minimum (1.2) at >1624masl. Without feeding an adult fly survived upto 3 days. It can be speculated that besides other meteorological factors, elevation affects geographical distribution of fly and its subsequent biological parameters.