Factors responsible for stage-specific mortality and sex ratio adjustment in Zygogramma bicolorata Pallister on parthenium in field conditions

Stage specific mortality and sex ratio adjustment in Zygogramma bicolorata Pallister (Coleoptera: chrysomelidae), were evaluated monthly for two consecutive years, 2010 and 2011, in field conditions on Parthenium hysterophorus L. Development of immature stages was considerably affected during the cold seasons of 2010 and 2011, and it was completely arrested in January. Similarly, the mortality survival ratio and indispensable mortality were higher in December, as compared to other months. Generation mortality (K-value) was decreased in May and then further increased from September to December, in both years. A non-significant difference (P < NS) in K-values were evident in July and August 2010, as well as in June and July 2011. Different abiotic and biotic factors may have influenced the mortality of the various immature stages. Greater mortality of eggs was due to their infertility in December. Similarly, mortality of 1st and 2nd instar was significantly high in Feburary, March, October, November and Dec...