Factors responsible for estivation in spotted stem borer, Chilo partellus (Swinhoe)

Abstract

Diapause is an important adaptive trait in certain groups of insects at a particular stage, which contribute in controlling insect ecology, phenology, and physiology. Considering the importance of various factors in appropriate combinations, we studied effects of different temperature and photoperiod conditions on larval morphometrics, development, induction, and termination of estivation, and overall mortality due to estivation in Chilo partellus (Swinhoe). Weight, length, and head capsule width of C. partellus larvae significantly increased with increase in temperature and photoperiod treatments upto certain age and duration of exposure. According to Dyar's ratio, overall head capsule width progressed geometrically with minimum constant ratio of 1.20, and second‐degree polynomial regression equations were best fitted to all the test treatment conditions. The mortality of diapausing C. partellus individuals varied between 7.0% and 37.3% under different constant and varying temperature and photoperiod regimes, which at 38°C + 14L:10D reached upto 100.0%. However, the exposure to 30°C + 12.5L:11.5D and 32°C + 13L:11D along with dry food accelerated the process of estivation, wherein the diapause larval survival was significantly higher and overall mortality of individuals due to diapause was lower suggesting these conditions appropriate for induction of estivation in C. partellus. These studies have implications for better understanding the bioecology and population regulation system under varying climatic conditions and devising novel strategies for management of C. partellus.

Genetic regulation of diapause and associated traits in Chilo partellus (Swinhoe)

“…Further, the greater fecundity, egg hatching, larval survival, termination of diapause and adult emergence in the progenies of nondiapause strain and the crosses involving either of the parent from nondiapause in comparison to diapause and post-diapause strains and their crosses suggest that the parental experience play an important role in inheritance of diapause in the progenies. Earlier reports of 15 to 65% diapause in C. partellus under different temperature and photoperiod conditions in the laboratory shows that apart from parental diapause history, asynchrony in diapause inducing stage and environmental conditions, and genetic segregation could also be influencing the induction of diapause in the progenies 14,15 . Diapause in C. partellus has also been found to affect certain morphological features like larval weight, length, and head capsule width 9,10,14,32 .…”

“…Formation of different diapause and nondiapause C. partellus populations. The late 4 th to early 5 th instar larvae of C. partellus from the above described respective cultures were exposed to earlier standardized hibernation (10 ± 1 °C + 10 L:14D) and aestivation (32 ± 1 °C + 13 L:11D) inducing conditions along with dry diet 14,15 . As a result of diapause treatment, the larvae showing any kind of diapause symptoms described by Dhillon and Hasan 32 were considered to be in diapause.…”

“…As a result of diapause treatment, the larvae showing any kind of diapause symptoms described by Dhillon and Hasan 32 were considered to be in diapause. In general, the dormancy duration in C. partellus varies from 45 to 50 days in different agro-ecosystems 14,15 . The diapausing larvae thus obtained were kept undisturbed at the respective treatment conditions up to 45 days, and afterwards exposed to diapause termination conditions (fresh artificial diet; 27 ± 1 °C, 70 ± 5% RH and 12 L:12D conditions).…”

“…These studies further suggested that the use of varying photoperiod and temperature regimes, and different cross-mating combinations are integral to better understand the inheritance of diapause in insects. In this view our recent studies revealed that both temperature and photoperiod combine are critical for induction and termination of diapause in C. partellus 14,15 . Dhillon and Hasan 32 elaborated that the larvae of C. partellus pass through hibernation under North Indian and aestivation under South Indian environmental conditions.…”

“…It undergoes facultative diapause as mature larvae inside the stems or stubbles of sorghum and maize 29,30 . Our earlier studies have generated comprehensive information on critical threshold conditions for induction and termination of diapause, duration of diapause, phenology of diapausing larvae, supernumerary moults, effects of diapause on post-diapause development and reproductive physiology, population buildup after diapause, and temperature-based development model of diapausing larvae in C. partellus 11,14,15,31,32 . Recent studies although revealed strong gene by environment interaction effects on diapause induction and incidence in some lepidopteran insect species, where inheritance patterns and dominance were found dependent on the photoperiod 27,33,34 .…”