Changes of Cold Hardiness, Supercooling Capacity, and Major Cryoprotectants in Overwintering Larvae of <I>Chilo suppressalis</I> (Lepidoptera: Pyralidae)

Abstract

The rice stem borer, Chilo suppressalis Walker, which is a key rice pest in northern parts of Iran, overwinters in rice stubble and weeds as mature larvae. Diapause of this pest is initiated between October to November and terminates in March. Seasonal variations in the supercooling point, survival at low temperatures, and sugar contents were studied in field-collected larvae during different phases of diapause. Ambient temperature was lowest in January and February when larvae were at the highest diapause intensity and achieved a high degree of cold hardiness at -10, -15, and -20 degrees C. Glycerol, a major cryoprotectant, reached a peak in January. It appeared that cold hardiness in the larvae is closely associated with the diapause. For the first time, this study suggests that glucose and glycogen are converted to glycerol during cold seasons, but trehalose has no definite role in the interconversion. During the coldest months, supercooling points (SCPs) increased (around -11 degrees C), and larvae could survive below their SCP values, showing that overwintering larvae of C. suppressalis are freeze tolerant in Iran. Our findings suggest that cold hardiness and diapause are essential components for this species. The overwintering larvae have high capacity of cold hardiness and can overcome severe winters. Understanding of cold hardiness and overwintering behavior of this species may help in integrated pest management of the rice stem borer in paddy fields.

Gene expression, metabolic regulation and stress tolerance during diapause

“…Trehalose build up is thought to be essential for continued existence of B. antarctica, but this mechanism is not employed by all organisms that tolerate dehydration or cold. For example, resting eggs of the rotifer B. plicatilis are not enriched in mRNA encoding trehalose-6-phosphate, a key enzyme in trehalose synthesis, leaving the role of this disaccharide uncertain even though the organism lives through desiccation [14], nor does trehalose increase in overwintering diapause larvae of the rice stem borer C. suppressalis [182].…”

“…Glycerol, possibly arising from glucose and glycogen, functions as a cryoprotectant by reducing freezing temperature, curbing ice crystal growth and shielding against cold-induced macromolecule disruption [3,127,181,182]. Glycerol potentially has a protective role in diapausing organisms.…”

“…This level is maintained in diapause pupae although it declines upon diapause termination and the initiation of quiescence [118]. Glycerol also peaks in diapause larvae of C. suppressalis, with maximal accumulation coinciding with the most intense diapause and greatest cold hardiness [182].…”

Control Effect of Insecticides against Chilo suppressalis Walker of Native Miscanthus in Korea

“…이화명나방(Chilo suppressalis Walker, Rice stem borer)은 유충이 벼과 식물을 가해하는 대표적인 해충으로 주로 동 남아시아 각국 및 호주 북부 등에 분포하며 국내에서 월동 하는 대표적인 벼의 해충이다 (Atapour and Moharramipour, 2009;Lee and Park, 1991;Song et al, 1982;Choi et al, 1976). 우리나라에서는 과거 1960년대에 벼에 다수 발생하 여 그 피해가 심각한 제 1 해충이었으나 1970년대 초반부 터 보급된 다수성 품종과 이에 따른 재배법 변화, 특히 조 기 이앙, 조기 수확 등으로 인한 월동율 저하, 집중약제방 제 및 기계수확 등의 복합적 요인으로 인하여 유충 발생량 이 감소하였다.…”

Overwintering pattern of larvae of Chilo suppressalis Walker in the bioenergy crop Miscanthus sacchariflorus cv. Geodae 1

“…(Atapour ＆ Moharramipour, 2009;John et al, 2014;Yu, 1980). 하지만 본 연구결과, 억새에 기주하는 이화명나방 유충의 월동장소는 줄기 기부 또는 지하경과 같이 지하부위 라는 점이 현재까지 알려진 벼에서 기주하는 이화명나방의 유충과는 다른 월동형태를 보이는 것으로 최초 확인되었다.…”