Effects of lectins, CRY1A/CRY1B Bt δ‐endotoxin, PAPA, protease and α‐amylase inhibitors, on the development of the rice weevil, Sitophilus oryzae, using an artificial seed bioassay

Abstract

AbstractAn artificial maize seed bioassay was developed to evaluate potential resistance factors against the rice weevil, Sitophilus oryzae. Weevils reared in artificial seeds compared to those reared in whole maize seeds: (i) developed faster, (ii) had similar within‐seed developmental mortalities, (iii) were lighter in weight upon emergence and (iv) oviposited the same number of eggs. Using this bioassay we found that E‐64, a cysteine protease inhibitor, decreased the number of emerged adults per seed and delayed within‐seed developmental time, suggesting that the rice weevil utilizes a cysteine protease to digest its dietary protein. Weevils fed inhibitors of trypsin and chymotrypsin, Bowman‐Birk and Kunitz inhibitors respectively, developed normally. Para‐amino‐l‐phenylalanine (PAPA), a non‐protein amino acid implicated as an insect resistance factor in Vigna vexillata, was lethal at dietary levels of 0.2% (w/w) and higher. An extract from Amaranthus caudatus seeds delayed the developmental time of the rice weevil at dietary levels of 0.2% (w/w) and increased mortality at dietary levels of 1.0% (w/w). Several proteins tested, including Griffonia simplicifolia agglutinin II, phytohemagglutinin extract containing common bean α‐amylase inhibitor, pokeweed agglutinin, Bacillus thuringiensis CRY1A/CRY1B endotoxin, and an α‐amylase inhibitor from wheat, had no effect on the rice weevil. The artificial maize seed bioassay was adapted by pelleting the seed for use with an ultrasonic insect feeding monitor to determine the finding activity of rice weevils as they developed from egg hatch to pupation.