Cedric Gillott

New Insights into Peritrophic Matrix Synthesis, Architecture, and Function

The peritrophic matrix (PM) is a chitin and glycoprotein layer that lines the invertebrate midgut. Although structurally different, it is functionally similar to the mucous secretions of the vertebrate digestive tract. The PM is a physical barrier, protecting the midgut epithelium from abrasive food particles, digestive enzymes, and pathogens infectious per os. It is also a biochemical barrier, sequestering and, in some cases, inactivating ingested toxins. Finally, the PM compartmentalizes digestive processes, allowing for efficient nutrient acquisition and reuse of hydrolytic enzymes. The PM consists of an organized lattice of chitin fibrils held together by chitin binding proteins. Glycans fill the interstitial spaces, creating a molecular sieve, the properties of which are dependent on the immediate ion content and pH. In this review, we have integrated recent structural and functional information to create a holistic model for the PM. We also show how this information may generate novel technologies for use in insect pest management.

Parasitoids, predators and PCR : the use of diagnostic molecular markers in biological control of Arthropods

Abstract:  The polymerase chain reaction (PCR) revolutionized the field of diagnostics, and today it has routine applications in medical, veterinary, forensic and botanical sciences. The fields of biological control and insect pest management have generally been slow to adopt PCR‐based diagnostics in comparison with other fields of science. However, there has been increasing interest in the use of molecular diagnostic tools in arthropod biological control. In applied entomology, molecular techniques have generally been used for insect identification and systematics; however, PCR‐based techniques are increasingly becoming recognized as valuable tools in ecological studies. Here, we review research that has used PCR‐based techniques for parasitoid and predator/prey identification and detection, and place these studies in the context of their contributions to biological control of arthropods. The status and future directions of diagnostic molecular markers in applied entomology and insect pest management are also discussed.

Contribution of male-produced proteins to vitellogenesis in Melanoplus sanguinipes

The transfer during copulation of radioactively labelled male accessory reproductive gland (ARG) protein and its accumulation by the ovary of Melanoplus sanguinipes have been studied. Most of the transferred material leaves the spermatheca within 24 hr and enters the haemolymph from which it can be accumulated by the ovary. Injection of labelled male ARG protein into vitellogenic females demonstrates that during the first 24 hr after injection, accumulation by the ovary is rapid. Immunoprecipitation and immunoelectrophoretic studies indicate that some of the ARG protein is accumulated unchanged. It is proposed that when the male transfers several spermatophores during copulation, he may make a significant contribution of protein to the developing oocytes.

Development of accessory reproductive glands and its control by the corpus allatum in adult male Melanoplus sanguinipes

Abstract Changes in the protein content of and the rate at which labelled protein appears in the accessory reproductive glands (ARG), fat body, and haemolymph were studied in normal and allatectomized (CA − ) males of the migratory grasshopper, Melanoplus sanguinipes . In addition, the effects of treatment of CA − insects with synthetic juvenile hormone (SJH), copulation, and removal of the ARG were examined. In normal males the protein content of the ARG increases linearly during the first 14 days after emergence. Incorporation of label by the ARG is maximal at day 7 and then decreases until, at day 14, it is the same as at day 1. The protein content of the fat body and haemolymph increases up to day 10 then declines, whereas changes in the uptake of label by the fat body and haemolymph parallel those of the ARG. Removal of the corpora allata (CA) prevents the normal increase in protein content of the ARG, but the protein content of the fat body and haemolymph increases steadily throughout the 14 days. Incorporation of label into the ARG, fat body, and haemolymph remained low throughout the experiment. Treatment of CA − insects with SJH, or copulation, stimulates the uptake of label by the ARG, fat body, and haemolymph and also results in an increase in their protein content. Removal of the ARG leads to an increase in the protein content of the fat body and haemolymph. Uptake of label by the fat body remains low after the operation. Although the rate at which labelled protein appears in the haemolymph is high initially, it declines steadily to day 14. We conclude that the CA regulate ARG development. It is suggested that the fat body, under CA control, synthesizes proteins which are incorporated into secretions of the ARG. Further, it is proposed that the primary effect of copulation is activation of the CA.

Male accessory gland substance of Melanoplus sanguinipes: An oviposition stimulant under the control of the corpus allatum

Abstract The accessory glands of male Melanoplus sanguinipes contain an oviposition stimulant. Injection of gland extracts from mature males induces oviposition in 75 per cent of capable virgin females within 24 hr. Injection of gland extracts from allatectomized males produces no stimulatory effect. Gland extracts from mature males contain two antigens which cannot be detected in gland extracts from allatectomized males. However, both antigens can be detected in gland extracts from allatectomized males 3 days after treatment with juvenile hormone. Anion-exchange chromatography of mature gland extracts yielded two fractions which, when injected into virgin females, induced oviposition in 71 per cent of capable insects within 24 hr. These two fractions are immunologically identical to the two antigens which are absent from gland extracts of allatectomized males. We suggest that synthesis of the oviposition stimulant in Melanoplus is controlled by the corpus allatum. Injection of brain extract also induces oviposition in 100 per cent of capable virgin females within 24 hr. A possible role for the brain in the oviposition process is discussed.

Male insect accessory glands: Functions and control of secretory activity

Summary Paralleling the diversity of the class Insecta, the male accessory glands (MAG) exhibit a wide range of form, and their secretion serves a variety of functions, including spermatophore and mating plug formation, sperm activation, provision of nutrients to females, and, through production of fecundity-enhancing and/or receptivity-inhibiting substances, modification of female reproductive behavior. In most insects, juvenile hormone (JH) is important in the regulation of MAG secretory activity; specifically, JH controls the production of particular proteins in the secretion. However, the production of some proteins appears not to be influenced by JH; rather, their synthesis is regulated by ecdysteroids. During sexual maturation, JH and ecdysteroids seem to interact to bring about a specified temporal sequence of protein synthesis in the MAG.

Diamondback moth, Plutella xylostella (L.), feeding and oviposition preferences on glossy and waxy Brassica rapa (L.) lines

Abstract Host plant resistance research to date indicates that Brassica plants expressing the glossy leaf wax characteristic show some resistance to diamondback moth, Plutella zylostella (L.). In the present study oviposition and first-instar feeding preferences were examined on ‘Glossy’ and ‘Waxy’ near isogenic lines of Brassica rapa (L.). Feeding preference, growth and survival of later instar diamondback moth larvae also were examined. Although females did not discriminate between ‘Waxy’ and ‘Glossy’ plants for oviposition, there was a strong preference among first-instar larvae for ‘Waxy’ plants in the choice experiment. There were no significant differences in larval survival or fourth-instar feeding preference on any of the lines tested. The present experiment indicates that B. rapa expressing the glossy leaf wax characteristic shows some resistance to diamondback moth, similar to that observed previously with glossy B. oleracea . The resistance appears to have a behavioural basis and is expressed against early instar larvae.

A single-step multiplex PCR assay for the detection of European Peristenus spp., parasitoids of Lygus spp.

Abstract Lygus Hahn (Hemiptera: Miridae) are serious pests of agricultural and greenhouse crops throughout North America. In Europe, bivoltine Peristenus Förster (Hymenoptera: Braconidae) species have a significant impact on Lygus populations. Release and establishment of European P. digoneutis Loan in Lygus lineolaris (Palisot de Beauvois) populations in northeastern USA has renewed interest in the intended liberation of European parasitoids for Lygus control in Canada. Accurate identification of natural enemies is the cornerstone of biological control but conventional methods for identifying Peristenus species and estimating parasitism rates rely on tedious and time-consuming dissection and rearing methods. The present study describes species-specific PCR primers for three species of Peristenus, and the use of a multiplex PCR assay to detect P. digoneutis and P. stygicus Loan eggs and larvae from Lygus rugulipennis Poppius nymphs. Results indicate that the primers amplify uniquely sized, species-specific PCR products for the three species and are capable of detecting single eggs in parasitized nymphs within 3 days post-parasitism. Using a multiplex PCR assay, the primers maintain specificity and sensitivity, and allow detection of each of the three species in a single reaction. Although molecular diagnostics have previously been used in the identification of parasitoids and estimation of parasitism rates, this is the first time a single-step multiplex PCR protocol has been described.

A chitin deacetylase and putative insect intestinal lipases are components of the Mamestra configurata (Lepidoptera: Noctuidae) peritrophic matrix.

One‐ and two‐dimensional gel electrophoresis coupled with liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) was used to identify cDNA encoding a chitin deacetylase (McCDA1) and three insect intestinal lipases (McIIL1, McIIL2 and McIIL3) associated with the Mamestra configurata (bertha armyworm) peritrophic matrix. Recombinant McCDA1 was active and chitin deacetylase activities were detected in the midgut. McCDA1 and the McIIL genes were expressed exclusively in the midgut; however, McCDA1 and McIIL2 were expressed in all larval stages, whereas McIIL1 was expressed mainly in feeding larvae and McIIL3 primarily during the moult.

Characterization of an intestinal mucin from the peritrophic matrix of the diamondback moth, Plutella xylostella.

The peritrophic matrix (PM) of Plutella xylostella larvae was found to contain twelve integral and eighteen loosely associated proteins. An antiserum against Mamestra configurata integral PM proteins cross‐reacted with several P. xylostella PM proteins and was used to isolate a partial cDNA encoding an insect intestinal mucin (PxIIM). PxIIM was expressed primarily in the larval midgut. The deduced protein sequence of the partial cDNA contained three potentially glycosylated, mucin‐like domains and six cysteine‐rich chitin‐binding domains (CBDs). An additional chitin‐binding domain was proposed to reside at the amino terminus of the protein based on comparison with other IIM. The organization of mucin domains and CBDs exhibited features, including an internal triplet of regularly spaced CBDs and a carboxyl terminal CBD with two additional conserved cysteine residues, that were found to be common to other lepidopteran IIMs.