Body Sizes of Niphe elongata at Each Developmental Stage: Estimation of Nymphal Instars by Comparing Reared and Field-Collected Individuals

Abstract

Niphe elongata (= Lagynotomus elongatus) (Dallas) is a key rice pest prevalent throughout Japan in recent years. Understanding the occurrence of each developmental stage of this bug may help estimate the amount of damage and the appropriate timing for insecticide application. In this study, we investigated whether it is possible to estimate the instars of the bug nymphs using the size of each body part (head capsule width, pronotum width, and body length) as an index. To this end, we compared the body sizes of reared individuals at each developmental stage with the body size distribution of field-collected individuals to evaluate whether they fit. In the reared individuals, the range of size measurements of each body part did not overlap between the instar stages. The field-collected individuals could be separated into five groups based on the head capsule and pronotum widths, but not body length. A comparison of the body size measurements (all three) of each instar in the reared individuals and the field-collected groups revealed that they showed similar values, although many significant differences were observed. These results imply that the five groups of field-collected nymphs reflect each instar, suggesting that it is possible to estimate the nymphal instars using body size as an index. The data on head capsule width and pronotum width obtained from field-collected individuals in this study may be used to determine the instar stage of newly collected nymphs.