• Indian Entomologist

IARI and ICRISAT scientists unravel genetic regulation of diapause in maize stem borer

By Tanmaya Bhoi, Research Scholar

Diapause is an endocrine controlled arrested metabolic state to delay development or reproduction under unfavorable conditions. It controls physiological processes and morphological development during a particular stage of the life cycle. The insects undergoing diapause pass through a series of physiological events such as suppression of development and reproductive functions, arrested metabolic activity to conserve the reserves and resumption of normal developmental process on the onset of optimum climatic condition. Diapause being an adaptive but genetically regulated trait provide phenotypic plasticity to insects in response to environmental conditions. Genetic and genetic- environmental interaction has been found to be involved in the induction and termination of diapause.

To gain an understanding of the importance of diapause for ecological adaptation, it is important to study the regulation of diapause in insects. Collaborative research was carried out by scientists from ICAR-Indian Agricultural Research Institute, New Delhi lead by Dr. Mukesh K. Dhillon and International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Hyderabad lead by Dr. Hari C. Sharma. The test insect was maize stem borer, Chilo partellus (Swinhoe). It is widely distributed in tropical and temperate areas in Asia and Africa and is a serious pest of maize and sorghum. It undergoes facultative diapause as mature larvae inside the stems or stubbles of sorghum and maize.

Genetics of diapause in C. partellus was studied by crossing the hibernating (HD), aestivating (AD), post-hibernating (PHD), post-aestivating (PAD), and nondiapause (ND) strains. 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 a 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 the outbreak of C. partellus. Finally, it was revealed that diapause, developmental and morphometric traits in C. partellus are governed by overdominance gene effects, and mainly depend on parental diapause history.

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