The effects of artificial diets on the anterior intestinal cell ultrastructure of Rhodnius prolixus (Hemiptera:Reduviidae)

Mated female Rhodnius prolixus were fed diets of washed rabbit erythrocytes (RBC), rabbit plasma, edestin (a plant storage protein) in Ringer's or Ringer's solution alone. All diets contained 1 mM ATP. The effects of these diets on anterior intestinal cell ultrastructure were evaluated and compared to changes induced by normal blood feeding. Separation of basal labyrinth membranes was induced earlier after Ringer's-feeding than with all other diets. Normal modifications of the rough endoplasmic reticulum (rer) were observed only in response to blood components, while rer cisternae were swollen shortly after edestin feeding. Normal modifications to lysosomal structure were induced by plasma and RBC feeding, but changes were also observed with the non-blood diets. Production of extracellular membrane layers (ECML) by the microvilli occurred in response to each diet: plasma-feeding induced considerably early ECML formation, but prolonged ECML proliferation was greatest after RBC feeding. Storage inclusions were most prominent in cells of plasma-fed insects. Initial changes in the basal labyrinth may be induced by a high luminal fluid: protein ratio; in the rer by blood factor(s); and in lysosomes by plasma factor(s). Gut distention initiates ECML production but continued proliferation is regulated by the midgut contents.     

Thermal denaturation of rat pulmonary and testicular angiotensin-converting enzyme isozymes. Effects of chelators and CoCl2

In an attempt to assess the biochemical consequences resulting from structural differences between rat pulmonary and testicular angiotensin-converting enzyme, the thermal stability of crude and purified preparations of each enzyme was compared. Structural heterology was verified by molecular weight determinations and by peptide mapping after limited proteolysis with Staphylococcus V8 proteinase. Thermal stability was monitored by changes in catalytic activity following incubations at 55°C in the presence of chelators and CoCl₂. Purified pulmonary angiotensin-converting enzyme was more sensitive to inhibition by the chelators EDTA and 1,10-phenanthroline and by the site-directed inhibitor captopril than was the testicular isozyme. Although the pulmonary holoenzyme was unaffected by cobalt, the testicular holoenzyme was inhibited by cobalt in a concentration-dependent manner. Crude pulmonary angiotensin-converting enzyme was significantly more resistant to thermal denaturation than its crude testicular counterpart. The differences in the thermal lability of each isozyme were still present in purified preparations, although the purified enzymes appeared to be more thermally stable than their crude counterparts. Both chelators and cobalt markedly potentiated the thermal denaturation of each isozyme. These data suggest that the structural heterology of the pulmonary and testicular isozymes may affect the interaction of zinc with the respective enzymes and that zinc may contribute to the structural integrity and thermal stability of angiotensin-converting enzyme in each tissue.     

Defensive larval secretions of leaf beetles attract a specialist predator Parasyrphus nigritarsis

1. Noxious larval secretions of leaf beetles, which repel generalist predators, do not deter specialist syrphid fly predators (genus Parasyrphus ). These flies cause considerable mortality to the beetles, but little is known about their foraging behaviour.
2. Larvae of Parasyrphus nigritarsis were attracted to the volatile larval secretions produced by two prey species Phratora vitellinae and Linaeidea aenea. Parasyrphus nigritarsis feeds on both beetles in nature. Phratora vitellinae feeds on willows and utilizes host plant compounds for secretion production, while the alder-feeding L. aenea produces an autogenous secretion.
3. Fly larvae were strongly attracted to pieces of filter paper treated with larval secretion of the beetles. They attempted to feed on them for up to 7 min, and were equally attracted to the secretions of Ph. vitellinae and L. aenea . Fly larvae were also attracted to pure salicyl aldehyde, the main component of the secretion of Ph. vitellinae .
4. Fly larvae searched extensively for prey on leaves that had been damaged by beetle larvae. They also followed trails made with solutions containing faecal matter of prey larvae. They showed no differential preference for Ph. vitellinae or L. aenea , but always rejected larvae of the non-prey leaf beetle Agelastica alni .
5. Beetle secretions thus play an important, but unexpected, role in the feeding behaviour of P. nigritarsis . This predator uses the beetle secretion to locate its prey. The implications of these results for three trophic level interactions are discussed.