Abstract
Diapause is an endocrine controlled arrested metabolic state to delay development or reproduction under unfavorable conditions. To gain an understanding of importance of diapause for ecological adaptation, it is important to study regulation of diapause in insects. We examined genetics of diapause in Chilo partellus by crossing the hibernating (HD), aestivating (AD), post-hibernating (PHD), post-aestivating (PAD), and nondiapause (ND) strains. Reciprocal crosses were also made to gain full understanding of diapause regulation and the maternal effects, if any. Data were recorded on fecundity, egg hatching, larval survival, diapause induction and termination, adult emergence, and morphometrics of larvae, pupae and adults in the parents (P1, P2), F1 hybrids, and the reciprocal crosses. Genetic analysis showed that AD strain is general combiner, which also improved egg hatching, larval survival, diapause termination, adult emergence and proportion of females in the progenies. Incidence of diapause was highest in HD × AD, whereas termination was greatest in PHD × AD. However, ND strain and its reciprocal crosses with other strains did not exhibit any noticeable developmental response associated with diapause. Specific combining ability analysis suggested that where PHD and AD strains exist together there will be likely reduction in diapause incidence, increased survival with greater fitness and faster multiplication of their progenies resulting in outbreak of C. partellus. Degree of dominance estimates revealed that diapause, developmental and morphometric traits in C. partellus are governed by over dominance gene effects, and mainly depend on parental diapause history.
Highlights
Diapause is an endocrine controlled physiological state of arrested metabolic activity during a particular stage of insect development to survive under predictable adverse climatic conditions[1,2,3,4]
The cross-mating among the adults of diapause and nondiapause strains and their F1 progenies within and across geographical regions is very likely, and there is a possibility of genetic polymorphism within and/or among the C. partellus populations
Egg laying by C. partellus females, egg hatching and larval survival were significantly higher in the cases where either of the parent from nondiapause strain was crossed with a parent from diapause or post-diapause strains as compared to other cross combinations, there were a few exceptions (Table 1)
Summary
Diapause is an endocrine controlled physiological state of arrested metabolic activity during a particular stage of insect development to survive under predictable adverse climatic conditions[1,2,3,4]. Recent studies 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] 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. The cross-mating among the adults of diapause and nondiapause strains and their F1 progenies within and across geographical regions is very likely, and there is a possibility of genetic polymorphism within and/or among the C. partellus populations To understand such a complex population regulation mechanism, there is an urgent need for intensive genetic research on insects to explore alternative ways to manage insect pests of economic importance. Present studies were planned to investigate: i) the genetic components of diapause regulation and developmental traits, ii) effect of parental genetic background on diapause and related traits, and iii) effect of frequency of type(s) of pre-existing strain(s) on diapause incidence, developmental traits, and likely rate of C. partellus population buildup under given climatic conditions
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