APPLICATION OF DYAR'S LAW IN INSTARS IDENTIFICATION OF THE INDIAN PREDACEOUS EARWIG, LABIDURA RIPARIA (PALLAS) FORM BENGALENSIS (DHORN) (DERMAPTERA : LABIDURIDAE) AS AN OCCASIONAL PEST OF POTATO IN COLD STORES OF UTTAR PRADESH INDIA

摘要

The surface pterygote earwig, Labidura riparia (Pallas) form bengalensis (Dohrn) was successfully reared for the first time to study the biology, host specificity and habits in the laboratory at an ambient temperature (27 +/- 2 degrees C) and (76 +/- 5%) R.H. The test species is omnivorous but preferred small moribund insects except lepidopteran and dipteran. However, this the first record that this insect occasionally damaging potato tubers in temporary field storage and cold storage in Uttar Pradesh. The matured insect bores in to the potato tubers and rendered them worthless. The females showed absolute parental-care. The life history developed through hemi-metamorphosis having five nymphal stages in both the sexes. The stadias greatly differs from each other. The duration of the five stadias ranged from 49-73 days. In the present study the close proximity between the mean, observed and calculated widths of head-capsule and the increase in widths of head-capsules of different nymphal instars fall them in to five well defined instars which characterized as nymphal stages in a geometrical progression, indicates the correct applicability of the Dyar's law. The line graph did not cut the 450 line. The growth line in between the two nymphal stages is an exact straight line and did not intersects the 45 line thus revealing that the nymphal stages were five in both the sexes. The variation in the value of the linear progression factor shows that progression principle is of no doubtful significance. In males the average ratio of increase of head-capsule width was 1.519 while in females it was 1.280. The values of widths of head-capsules in successive instars of males was slightly higher than the females, although followed a fairly regular geometrical progression. Conclusively Dyar's law is very important and useful for determining the number of instars in the life cycle of an insect.