Head Capsule Width, Body Weight and Length Measurements for Instar Determination in Mason Bee (Osmia cornifrons) Larvae

Abstract

Osmia cornifrons is a cavity-nesting solitary species used as an apple pollinator in Korea. We collected Osmia spp larvae to examine potential correlations of larval stage. The head widths of from 1<SUP>st</SUP> to the 5<SUP>th</SUP> instar ranged from 0.4±0.1 to 1.3±0.3 mm, and growth rate of each instar was significantly highest between 1<SUP>st</SUP> and the 2<SUP>nd</SUP> instar. The fitness regression model for the head capsule width was analyzed. The head capsule width plotted against the number of instars resulted in a regression line of y=0.146x+0.551, R²=0.838. The body weights of the larvae increased with larval developmental stage, and the coefficient of variation of larval weights was high. However, the calculated regression line was y=5.122x² -12.154x+11.444, R²=0.900. The growth ratio of the larval length was clearly maximal between the 3<SUP>rd</SUP> and 4<SUP>th</SUP> instars, while that of 5<SUP>th</SUP> instar larvae was decreased. The calculated regression line is y=2.595x+0.472, R²=0.920. The result suggests that measurements of head capsule width, weight and length may be useful as a method to determine larval instar.