The uptake of metals from food and water sources by insects is thought to be additive. For a given metal, the proportions taken up from water and food will depend both on the bioavailable concentration of the metal associated with each source and the mechanism and rate by which the metal enters the insect. Attempts to correlate insect trace metal concentrations with the trophic level of insects should be made with a knowledge of the feeding relationships of the individual taxa concerned. Pathways for the uptake of essential metals, such as copper and zinc, exist at the cellular level, and other nonessential metals, such as cadmium, also appear to enter via these routes. Within cells, trace metals can be bound to proteins or stored in granules. The internal distribution of metals among body tissues is very heterogeneous, and distribution patterns tend to be both metal and taxon specific. Trace metals associated with insects can be both bound on the surface of their chitinous exoskeleton and incorporated into body tissues. The quantities of trace meals accumulated by an individual reflect the net balance between the rate of metal influx from both dissolved and particulate sources and the rate of metal efflux from the organism. The toxicity of metals has been demonstrated at all levels of biological organization: cell, tissue, individual, population, and community. Much of the literature pertaining to the toxic effects of metals on aquatic insects is based on laboratory observations and, as such, it is difficult to extrapolate the data to insects in nature. The few experimental studies in nature suggest that trace metal contaminants can affect both the distribution and the abundance of aquatic insects. Insects have a largely unexploited potential as biomonitors of metal contamination in nature. A better understanding of the physicochemical and biological mechanisms mediating trace metal bioavailability and exchange will facilitate the development of general predictive models relating trace metal concentrations in insects to those in their environment. Such models will facilitate the use of insects as contaminant biomonitors.

Aquatic insects and trace metals: bioavailability, bioaccumulation, and toxicity.

Antiviral activity of a serine protease from the digestive juice of Bombyx mori larvae against nucleopolyhedrovirus.

The genus Baculovirus contains three subgroups of viral types: (1) nuclear polyhedrosis viruses (NPVs), (2) granulosis viruses (GVs), and (3) nonoccluded baculoviruses. While little information is available for viruses from the third subgroup, several aspects of the infectivity and mode of action of NPVs and GVs have been studied. The most common route of entry of a virus into an insect host is per os, and both virus types enter midgut cells (primary site of infection) by membrane fusion. However, two distinct mechanisms of virus uncoating occur among the baculoviruses: NPVs uncoat within the nucleus, whereas GVs uncoat at the nuclear pore complex. Baculoviruses of subgroup 3 appear to uncoat by either mechanism. In addition to replicating within the nucleus, NPV inoculum virus may pass through the intestinal epithelium immediately after ingestion, thereby establishing a systemic infection of the hemocoel prior to virus replication in midgut cells. The GVs do not appear to pass through midgut cells as rapidly as NPVs and in general, the developmental cycle of GVs is longer than that of NPVs. NPVs have been grown in cell culture while GVs have not.

Infectivity and mode of action of Baculoviruses

To gain an insight into the effects of different diets on growth and development of the domesticated silkworm at protein level, we employed comparative proteomic approach to investigate the proteomic differences of midgut, hemolymph, fat body and posterior silk gland of the silkworms reared on fresh mulberry leaves and on artificial diet. Seventy-six differentially expressed proteins were identified by MALDI TOF/TOF MS, and among them, 41 proteins were up-regulated, and 35 proteins were downregulated. Database searches, combined with GO analysis and KEGG pathway analysis revealed that some hemolymph proteins such as Nuecin, Gloverin-like proteins, PGRP, P50 and beta/-N-acetylglucosamidase were related to innate immunity of the silkworm, and some proteins identified in silkworm midgut including Myosin 1 light chain, Tropomyosin 1, Profilin, Serpin-2 and GSH-Px were involved in digestion and nutrition absorption. Moreover, two up-regulated enzymes in fat body of larvae reared on artificial diet were identified as V-ATPase subunit B and Arginine kinase which participate in energy metabolism. Furthermore, 6 down-regulated proteins identified in posterior silk gland of silkworm larvae reared on artificial diet including Ribosomal protein SA, EF-2, EF-1gamma, AspAT, ERp57 and PHB were related to silk synthesis. Our results suggested that the different diets could alter the expression of proteins related to immune system, digestion and absorption of nutrient, energy metabolism and silk synthesis poor nutrition and absorption of nutrition in silkworm. The results also confirmed that the poor nutrient absorption, weakened innate immunity, decreased energy metabolism and reduced silk synthesis are the main reasons for low cocoons yield, inferior filament quality, low survival rate of young larvae and insufficient resistance against specific pathogens in the silkworms fed on artificial diet.

Comparative proteomic analysis between the domesticated silkworm (Bombyx mori) reared on fresh mulberry leaves and on artificial diet.

Publisher Summary This chapter discusses three separate aspects of excretion, as first proposed by Maddrell: removal of molecules that are undesirable or perhaps even poisonous at all except very low concentrations; excretion of molecules that are not toxic but merely useless, and that would become obstructive if allowed to accumulate; and excretion of molecules that are useful or essential but are present to excess. This includes excretion of water and physiological ions in some circumstances. The chapter attempts to link recent advances in the understanding of the physiology, biochemistry, genetics, molecular biology, and chemical ecology of insect excretory mechanisms to the fundamental principles of design established several years ago. For example, the primary ATP-dependent transporter in insect epithelia was referred to in the literature until the early 1990s as the electrogenic alkali cation pump. The theme of this chapter is that studies of insect excretory mechanisms frequently provide illustrations of the Krogh principle; for a large number of problems, there will be some animal of choice or a few such animals on which it can be most conveniently studied. Adaptations to extreme environments, coupled with the large number of unusual food sources exploited by insects and their extraordinary diversity, provides a fertile ground for research into excretory mechanisms.

Insect Excretory Mechanisms

Effect of cadmium-feeding on tissue concentrations of elements in germ-free silkworm (Bombyx mori) larvae and distribution of cadmium in the alimentary canal.

The silkworm larvae reared on artificial diet were more susceptible to the infection per os with nuclear polyhedrosis virus than those reared on natural diet and furthermore the anti-viral activity in the digestive juice of the former was weaker than that of the latter. The fluorescent colours of the digestive juices from the larvae fed on natural or artificial diets, were different from each other, being red in the former and yellow in the latter. A protein having red fluorescence was fractionated from the digestive juice of silkworm larvae fed on natural diet, mulberry leaves. The fluorescent protein fraction inactivated the nuclear polyhedrosis virus and the inactivating potency was almost same both in the digestive juice and in the buffered solution containing this fluorescent protein fraction at nearly equal concentration of that in the digestive juice itself. It is concluded that this red fluorescent protein fraction may play an important role in the protective mechanism in silkworm larvae for per os infection by the silkworm nuclear polyhedrosis virus and that the fraction is not observed in the digestive juice from the larvae reared on artificial diet.

https://www.jstage.jst.go.jp/article/jjaez1957/12/4/12_4_189/_pdf

Inactivation of Nuclear Polyhedrosis Virus in the Digestive Juice of Silkworm Larvae, Bombyx mori L.

The Production of Anti-Viral Substance, a Red Fluorescent Protein, in the Digestive Juice of the Silkworm Larvae (Lepidoptera : Bombycidae)

The occult virus of nuclear polyhedrosis of the silkworm larvae

https://www.jstage.jst.go.jp/article/kontyushigen1930/36/1/36_1_39/_pdf

Fujiyoshi Matsubara

Papers

Effect of cadmium-feeding on tissue concentrations of elements in germ-free silkworm (Bombyx mori) larvae and distribution of cadmium in the alimentary canal.

Inactivation of Nuclear Polyhedrosis Virus in the Digestive Juice of Silkworm Larvae, Bombyx mori L.

The Production of Anti-Viral Substance, a Red Fluorescent Protein, in the Digestive Juice of the Silkworm Larvae (Lepidoptera : Bombycidae)

The occult virus of nuclear polyhedrosis of the silkworm larvae

Aseptic rearing of silkworm with prepared food