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larvae of certaln Insects were unable to develop l~orli~ally on soybean products.
Subsequently the trypslti inhibitors present 111 soybean uere shown to be toxic to the larv;ie
of tlour beetle, Tri6oiilr111 co~rfirslr~~~ (Llpke et al.. 1954). Following tliese early studies.
there I~JYC been riiany exa~i~ples of protcase ~~~l~ibrrors active against certalli inscct species.
both in ~n vltro assays agalnst insect gut proteases (Panneticr et al. 1907: Koiwa et al.
1998) and in in vivo artificial diet bioassays (Urwi~i ct al. 1997; Vain ct al. 1998). The tcrrn
"protcase" includes both "endopeptidases" and "exopcptidases" wlierc:is, thc tcrlii
"prote~nabe" 1s used to describc only "endopeptidases" (Ryan, 1900). Several lion-
lloniologoi~s farnilres of proteinase
inhibitors arc recognized anlong tlie animal,
microorgaliisriis and plant kingdom. Maijority of protei11;ise rnhibitors studicd in plarlt
kingdom originates fro111 three main fiimllies liarnely Ieguminosae, solanoceae and
graniineae (Ricliardsoli, 199 I).
A Iiirgr 11u111ber of protease rnliib~tor gc11i.s wit11 distilict niodes ofactioli liavc beeti
isolated from a wide range of crop species. Drvelop~ne~it of tra~isgenic crops lia\,e coriic ;I
long way from tlie tirst transgeliic developed by H~ldcr et al. (1987). Considering tlic I11gl1
cornplex~ty of proteaselinhibitor interactions ill host pest systems and the d~versity of
proteolytic elizyliies used by pests and palllogens ro liydrolyre dietary protelns or to cleave
peptide bonds in more specific processes (Graham et al. 1997), the choice of an appropilate
proreinane inhtb~tor (1'1) or set of PIS represents a primary determ~rl;int In the succcsa or
failure of any pest control strategy relying 011 protease inliibition. Firstly, tlle choice of
su~table PIS should be based oil a detailed understanding of the biological system assessed.
Resistant biotypes of insects may evolve aAer prolonged exposure to selection pressure
that is medlated by an insect~cidal proteln or plant resistance gene (Sparber, 1985). Seco~ld