Poster: Plant insect-nematode interactions

Abs # 499: Silkworm development is affected by mulberry biomineral deposits and phytoestrogens

Presenter:	Maier, Camelia G.-A, cmaier@mail.twu.edu
Authors	Maier, Camelia G.-A (A)   Moraru, Corina  (A)   Garrett, David C (B)   Johnson, Rebecca  (A)
Affiliations:	(A): Texas Woman's University (B): University of North Texas

Plants have evolved both constitutive and inducible strategies, such as accumulation of mineral depositions and phytoestrogens, to defend themselves against herbivores. Previous studies in our lab showed that female leaves contain significantly higher levels of oxalate and calcium deposits, and induced significantly higher estrogenic activity than male leaves of mulberry, Morus alba, Moraceae. We used the mulberry/silkworm system to investigate the impact of the above sexual dimorphism characteristics of mulberry on the performance and feeding behavior of silkworm populations. Silkworms preferred and performed better on male than female leaves. Total time of feeding on male leaves was twice as long as that of feeding on female leaves. Development was delayed for silkworms raised exclusively on female leaves. Although both male and female mulberry leaves contain same types of mineral deposits at the same anatomical location, insoluble oxalate concentrations and calcium carbonate deposits were significantly higher in female than male leaves (P= 0.033 and P=0.02 respectively, alpha=0.05). Silkworms avoided chewing on female leaf veins, which contained significantly higher concentrations of calcium oxalate deposits than the male veins. Extracts of female-fed silkworm feces induced lower estrogenic activities than the male-fed ones in a transgenic yeast system expressing the human estrogen receptor alpha, suggesting better assimilation by silkworms of phytoestrogens in fresh female leaves. Silkworms preferred and performed better on male mulberry leaves possibly due to low content of mineral depositions, oxalate, and phytoestrogen activity. Our results suggest a constitutive defensive role for mineral deposition and phytoestrogens against insect pests.