JH biosynthesis by corpora allata in Locusta migratoria and Schistocerca gregaria on artificial diet

S. Nakamura 1 & T. Okuda 2

1 International Centre of Insect Physiology and Ecology (ICIPE), P. O. Box 30772, Nairobi, Kenya; 2 National Institute of Sericultural and Entomological Science, 1-2 Ohwashi, Tsukuba, Ibaraki, Japan 305-8634

Ovarian development is arrested for about a month in long day-length and crowded conditions, while short day-length and crowded or long day-length and isolated conditions can prevent reproductive arrest in L. migratoria Tsukuba strain (Tanaka et al., 1993). When reared on artificial diet, ovarian maturation was delayed by 5 to 7 days compared with those on fresh leaves in L. m. migratorioides, indicating that factors such as photoperiod, population density and diet may modulate rate of reproductive development in L. migratoria. Isolated corpora allata (CA) from reproductively inactive females kept in long day-length conditions produced more JH in vitro than those from reproductively active ones maintained in a short day-length environment, and we found that allatostatic factors in the brain were involved in this paradoxical result (Okuda et al, 1996). Similarly, the rate of JH biosynthesis by the CA from reproductively active females on fresh leaves was consistently lower than reproductively less active ones on artificial diet. We found similar CA regulation occurring in L. m. migratorioides. It seems that adverse environmental conditions for reproduction or growth of the progeny, i.e. high population density and inferior quality artificial diet decelerated actual JH production by the CA due to allatostatic factors but the potential of the CA to produce JH was substantially enhanced. This is why the relationship between JH biosynthesis by the CA in vitro and ovarian development was negative. We also investigated JH biosynthesis by CA on different diets in S. gregaria and found that CA regulation by the brain was different to that in L. migratoria.

Index terms: JH biosynthesis, reproduction, Locusta migratoria, Schistocerca gregaria, artificial diet.

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