in vivo and in vitro studies of proteinase inhibitor action on the development and midgut proteinase activities of the sugarcane borer (Diatraea saccharalis) (Fabr., 1794)

Author(s)

Patricia Pompermayer

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2000-06-28
• Advisor: Marcio de Castro Silva Filho

Abstract

The objective of the present study was to evaluated, in vivo and in vitro, the action of soybean proteinase inhibitor (SPI) on the development and midgut proteinase activities of the sugarcane borer (Diatraea saccharalis) (Fabr., 1794). The major proteinase activities of D. saccharalis were characterized. The antímetabolic properties of the SPI, Kunitz and Bowman-Birk in vitro, before and after incorporation into artificial diet, in vivo, and its interference on population increase potential of the pest have been evaluated. Based on hydrolysis of the synthetic substrates, two major trypsin activities were identified (pH 8.0 and 9.0) and also a chymotrypsin activity with an optimum pH at 9.0. D. saccharalis trypsin and chymotrypsin display aIkaline pH optima, as observed to most Lepidoptera insects. The inhibition of trypsin and chymotrypsin activities in vitro,by SPI suggested that either, Kunitz and Bowman-Birk, could have a potential antimetabolic effect when ingested by these insect larvae. The incorporation of semi-purified extract SPI into an artificial diet of neonate larvae at 0.5% (w/w), significantly reduced the growth and development of the insect, reflecting an increase of the instar number and duration, and a significantly lower average weight. However, ingestion of SPI did not influence larval survival and the second generation of larvae fed SPI diet. In addition, there was an increase of the leveI of tryptic activity and a decrease of inhibition by the SPI in vitro. It was also observed that the diet nutrition value affect the insect susceptibility to the inhibitor. Studies on the fertility life table showed that lower net reproduction rates ((Ro), instantaneous rate of increase (Rm), and finite ratio of increase (λ), and the higher mean generation time (T) and the doubling time (Dt) were obtained from adults reared on diet supplemented with SPI. The observed differences potentially translate into large differences in population growth, indicating a potential value of SPI for protecting sugarcane plants against damage by D. saccharalis (AU)