Plutella xylostella L. (diamondback moth) is a pest of cruciferous plants. To understand the relationship among
protease inhibitors,
protease activities and the growth and development of this insect, the activities of midgut
proteases of P. xylostella larvae were determined in this study.
Protease samples were extracted from the midguts of P. xylostella larvae, and the
protease activities were determined using
enzyme specific substrates. The results showed that CaCl2,
EDTA, and
EGTA inhibited only the
trypsin. Among the common
protease inhibitors, phenylmethyl sulfonyl
fluorine (PMSF), Nα-p-methyl sulfonyl-
L-lysine chloromethylketone (
TLCK), Nα-methyl sulfonyl-
L- phenylalanine chloromethyl
ketone (
TPCK), soybean
trypsin inhibitor (
STI), and PMSF inhibited the total
protease, high-alkaline
trypsin (a
trypsin subtype with highly alkaline pH optimum), low-alkaline
trypsin (another
trypsin subtype with slightly alkaline pH optimum), and
chymotrypsin;
TLCK inhibited the total
protease and high-alkaline
trypsin, whereas
TPCK only activated the high-alkaline
trypsin activities.
STI had an inhibitory effect on all the
proteases. These results showed that
protease inhibitors had a certain extent inhibition to
protease activities in the larval midgut of P. xylostella and that
STI can potentially be used for effective pest control. The development of P. xylostella was delayed in the presence of different inhibitors. These effects were also related to the concentration of the inhibitor. A higher
STI concentration showed a longer lasting effect but lower effect in this study compared to that of
TLCK. The
protease inhibitors had some inhibitory effect on the synthesis and secretion of
proteases, and interfered with the
protease activity, thereby inhibiting the absorption of nutrients and delaying the growth and development of P. xylostella and reducing their ability to reproduce. These findings should provide the baseline information about using for effective pest management in the future.