Introduction Directory UMM :Data Elmu:jurnal:I:Insect Biochemistry and Molecular Biology:Vol30.Issue8-9.Sept2000:

Insect Biochemistry and Molecular Biology 30 2000 847–854 www.elsevier.comlocateibmb Juvenile hormone-mediated termination of larval diapause in the bamboo borer, Omphisa fuscidentalis Tippawan Singtripop a , Somsak Wanichacheewa a , Sho Sakurai b, a Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand b Department of Biology, Faculty of Science, Kanazawa University, Kanazawa 920-1192, Japan Received 31 October 1999; received in revised form 31 December 1999; accepted 25 January 2000 Abstract Larvae of the bamboo borer, Omphisa fuscidentalis are in diapause for more than nine months Singtripop, T., Wanichaneewa, S., Tsuzuki, S., Sakurai, S. 1999. Larval growth and diapause in a tropical moth, Omphisa fuscidentalis Hampson. Zool. Sci. 16, 725–733. To examine the endocrine mechanisms underlying this larval diapause, we assayed the responsiveness of the diapausing larvae to 20–hydroxyecdysone 20E and a juvenile hormone analogue JHA: S–methoprene. 20E injection caused the larvae to halt movement, followed by deposition of a pupal cuticle. Topical application of JHA induced pupation in a dose-dependent manner. JHA also induced pupation of the larvae whose brains were removed before JHA application. In those larvae, the prothoracic glands became active and competent to respond to brain extracts within seven days after JHA treatment, and the hemolymph ecdysteroid concentration began to increase 12 days after JHA application. These results indicate that JHA stimulates the prothoracic glands of diapausing Omphisa larvae, terminating larval diapause, in contrast with previous findings that JH inhibits the brain–prothoracic gland axis and thus maintains the larval diapause. Current results therefore suggest a novel regulatory mechanism for larval diapause in this species.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Methoprene; Prothoracic gland; 20–hydroxyecdysone; Ecdysteroid titer; Prothoracicotropic hormone

1. Introduction

Diapause is a strategy to survive seasons with environmental conditions that are inadequate for sustain- ing continuous development or maintenance of the organism Denlinger, 1985. In the tropics, diapause may occur in response to a period of drought which reduces the food supply Denlinger, 1986; Tauber et al., 1986. The bamboo borer, Omphisa fuscidentalis, is a univol- tine lepidopteran that experiences an annual severe dry season in Northern Thailand, Laos and Myanmar. In Chiang Mai Province, Northern Thailand, adults appear in August, in mid wet season, and lay egg clusters on newly grown bamboo shoots. Newly hatched larvae enter the internode to feed on the inner pulp. After they complete larval growth in September, the larvae enter Corresponding author. Tel.: + 81-76-264-5713; fax: + 81-76-264- 5977. E-mail address: ssakuraikenroku.kanazawa-u.ac.jp S. Sakurai. 0965-174800 - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 5 - 1 7 4 8 0 0 0 0 0 5 7 - 6 diapause and remain inside the internode of bamboo culm until the following June when they pupate. Bam- boo borer larvae are thus in diapause for nine months, from September until the following June Singtripop et al., 1999. The availability of food may be profoundly influenced by seasonal rhythms Denlinger, 1986. Rains stimulate an increase in plant growth, which provides a wealth of new food resources for many phytophagous insects. The long diapause is, therefore, important in maintaining synchrony between the insect life cycle and the phe- nology of the host plants in the tropics. Bamboo pro- duces new shoots in the wet season, and the shoots become hard by the end of the wet season. Therefore the long period of larval diapause in Omphisa appears to be well adapted to the recurring, annual dry–wet seasons Singtripop et al., 1999. Diapause in the larval or pupal stage is usually main- tained by a decrease in the hemolymph ecdysteroid titer Denlinger, 1985, due to a decrease in the biosynthetic activity of the prothoracic gland, which produces 3– 848 T. Singtripop et al. Insect Biochemistry and Molecular Biology 30 2000 847–854 dehydroecdysone andor ecdysone. Such a decrease is caused by depletion of prothoracicotropic hormone PTTH, a neuropeptide which is produced by two pairs of neurosecretory cells in the brain and which stimulates the prothoracic glands. In larval diapause, a high juvenile hormone JH titer in the hemolymph is reported to be involved in suppression of the brain–prothoracic glands axis, preventing the release of ecdysteroids for larval growth and pupation Denlinger, 1985. In fact, removal of CA from diapausing larvae causes a decrease in JH concentration, which induces an increase in hemolymph ecdysteroid, thus terminating diapause Yagi and Fukaya, 1974; Yin and Chippendale, 1979. During the long larval diapause in O. fuscidentalis, the hemolymph ecdysteroid concentration is low Singtripop et al., 1999. This indicates that JH might be involved in maintaining the larval diapause of the bam- boo borer, as in other lepidopteran larvae Yin and Chip- pendale, 1973. Application of JH analogue JHA, how- ever, terminated the larval diapause. In the present study, we report that in O. fuscidentalis, JH is not involved in maintenance of the larval diapause, but rather stimulates the prothoracic glands of the diapausing larvae.

2. Materials and methods