Reduction of Trehalase Activity and Morphological Changes of Reproductive Organs in the Red Flour Beetle, Tribolium castaneum (Coleoptera: Tenebrionidae), Induced by Latex from Paper Mulberry, Broussonetia papyrifera

Plant latex contains various compounds related to plant defensive roles against herbivores. The paper mulberry, Broussonetia papyrifera L. (Moraceae), produces latex in every part of the tree. The composition and properties of B. papyrifera latex have been reported; however, its effects on insects have not been reported. This study was conducted to examine the effect of B. papyrifera latex on the red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae). Trehalase activity was suppressed by latex extracts in vitro at various concentrations, and an examination of the fundamental properties of trehalase inhibitor revealed that it is a heat-stable and proteinaceous molecule larger than 10 kDa. The latex extract reduced insect body mass, egg production, and the number of larvae, pupae, and adults of T. castaneum in a concentration-dependent manner. The reproductive organs in both males and females were affected by latex treatment, resulting in a reduction in the size of mature oocytes and germarium in female beetles. Testicular lobes and accessory glands in male beetles also decreased in size. Trehalase activity in reproductive tissues was suppressed by latex, which led to the reduction of glucose content, but the amount of trehalose was not affected. These findings revealed that the latex of B. papyrifera contains components that suppress the trehalase activity, interfere with the growth and reproductive organs of the red flour beetle, and thus may contribute to the plant's defense strategy against this insect pest.