Phd Thesis 33 - eCommons@USASK - University of Saskatchewan

caterpillar, Malacosoma disstria, when the larvae were fed increasing amounts of dietary iron
(Barbehenn and Stannard, 2004). PMs may also serve as a molecular sieve and physically
exclude molecules through a process known as ultrafiltration (Barbehenn, 2001). Negatively
charged molecules are repelled by the similarly charged PM, referred to as polyanion exclusion
(Barbehenn, 2001). In Helicoverpa zea, the PM was demonstrated to scavenge hydroxyl radicals
in vitro and reduce the formation of hydroperoxides in midgut tissues exposed to a hydroxyl
radical generator, suggesting the PM may have antioxidant functions (Summers and Felton,
1996). When PM formation was inhibited by calcofluor in M. disstria and Orgyia leucostigma,
protein carbonyls, the most widely used marker of oxidative modification of proteins, increased
by two- to three-fold in the midgut epithelium confirming the radical scavenging antioxidant
feature of the PM (Barbehenn and Stannard, 2004). As such, the PM was considered to be a
“sacrificial antioxidant”.
1.2.4 The Peritrophic Matrix as a Target for Novel Methods of Insect Control
The PM is an attractive target for pest management strategies due to its intimate
involvement in digestive processes and role as a first line of defence against pathogens.
Compounds that interact with the PM have the potential to affect its physiochemical and
biological properties. A number of strategies that target the PM as a form of insect control are
outlined below.
1.2.4.1 Compounds that block or inhibit the passage of nutrients resulting in retardation of
larval growth
A variety of compounds may block PM pores thus compromising nutrient uptake and
digestive efficiency (Eisemann et al., 1994; Casu et al., 1997). Lectins, small carbohydrate
binding proteins, have been reported to interfere with insect growth and development and have
been suggested for use as selective tools for insect control (Czapla and Lang, 1990; Murdock et
al., 1990). For example, ingestion of wheat germ agglutinin decreased PM permeability, reduced
growth rate, and caused mortality of L. cuprina larvae (Eisemann et al., 1994). Interaction of
lectins with the PM may block nutrient passage in pores and decrease digestive efficiency by
preventing the passage of enzymes into the lumen and nutrients to the ectoperitrophic space. O.
nubilalis larvae fed wheat germ agglutinin for 24 h hypersecreted a multilayered abnormal PM in
9