Wednesday, December 13, 2006
D0575

Mulberry leaves are toxic to caterpillars: Mulberry latex rich in sugar-mimic alkaloids defends mulberry trees from caterpillars other than the silkworm, Bombyx mori

Kotaro Konno, konno@affrc.go.jp1, Hiroshi Ono2, Masatoshi Nakamura1, Naoya Wasano1, Ken Tateishi1, Chikara Hirayama1, Yasumori Tamura1, Makoto Hattori1, Akio Koyama1, and Katsuyuki Kohno3. (1) National Institute of Agrobiological Sciences, 1-2 Ohwashi, Tsukuba, Ibaraki, Japan, (2) National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki, Japan, (3) Japan Research Center for Agricultural Sciences, 1091-1 Maezono, Ishigaki, Okinawa, Japan

    Mulberry leaves (Morus spp.) have been used to rear the silkworm, Bombyx mori for thousands of years. However, we found that mulberry leaves are highly toxic to lepidopteran larvae other than the silkworm, B. mori, (such as the Samia ricini, Saturniidae and notorius pest species, Mamestra brassicae, Noctuidae ), due to the ingredients of the latex. The toxicity of mulberry leaves was lost when latex was washed off, and latex-added artificial diets showed toxicity. Mulberry (M. australis) latex contained very high concentrations of alkaloidal sugar-mimic glycosidase inhibitors reported to have anti-diabetic activities, such as 1,4-dideoxy-1,4-imino-D-arabinitol (D-AB1), 1-deoxy nojirimycin (DNJ), and 1,4-dideoxy -1,4-imino-D-ribitol. Their concentrations, altogether, in latex reached 1.5-2.5% (8-18% to dry weight) in several mulberry varieties, which were 100 times the concentrations previously reported from whole mulberry leaves. These sugar-mimicking alkaloids showed toxicities to caterpillars, but not to the silkworm, B. mori. Our results suggest that mulberry latex and sugar-mimicking alkaloids in it play key roles in defense of mulberry against insect herbivory, and also suggest the existence of some adaptive mechanisms in the silkworm, B. mori. This study shows, for the first time in long history of sericulture, the existence of strong latex-borne defense mechanisms in mulberry, and gives practical answer to mulberry-silkworm interactions.

Reference

Konno K. Ono H. et al. (2006) Proc. Natl. Acad. Sci. USA, 103, 1337-1341.



Species 1: Urticales Moraceae Morus australis (mulberry)
Species 2: Lepidoptera Bombycidae Bombyx mori (silkworm)
Species 3: Lepidoptera Saturniidae Samia ricini (Eri silk worm)