Evelyn B. Beckett

A light and electron microscope study of rickettsia-like organisms in the ovaries of mosquitoes of the Aedes scutellaris group.

The ovaries from some members of the Aedes scutellaris group were examined by light and electron microscopy to locate rickettsia-like organisms, and Culex pipiens fatigans was used as a control. It was found that light microscopy was unsatisfactory for this purpose since none of the available staining techniques demonstrates the organisms clearly and diagnostically. With the electron microscope it was shown that the organisms were by no means as common in the mosquitoes of the A. scutellaris group as in C.p. fatigans; they were quite frequently seen in A. polynesiensis, of sporadic occurrence in A. malayensis, rare in A. tabu and have not yet been identified with certainty in A. cooki.

Histochemical observations on Aedes Aegypti infected with larvae of Brugia Malayi

Abstract Protein-bound sulphydryl and amino groups, and the enzyme L-leucine amino-peptidase were studied histochemically in Aedes aegypti parastized by infective Brugia malayi filarial larvae 9–10 days old. The distribution of these protein-linked groups and of this enzyme in the mosquito thorax is described in detail. The concentration of sulphydryl and amino groups in the flight muscle fibres is similar to that in mammalian skeletal muscle. The presence of larvae within the fibres causes no change in either the concentration or distribution of these groups, except in the rare instances when small patches of amorphous material are formed adjacent to a larva. No aminopeptidase activity is found associated with normal or with parasitized muscle fibres, and the larvae are themselves either completely or virtually negative. The lack of observable histochemical changes correlates well with the absence of histological damage. These results are compared with those obtained in a histochemical study of the effects of the larvae of the nematode, Trichinella spiralis , on mammalian muscle. Possible reasons for the observed differences are discussed.

The survival and development of subperiodic Brugia malayi and B. pahangi larvae in a selected strain of Aedes aegypti.

Abstract The development of Brugia malayi and B. pahangi larvae in the thoracic flight muscles of a selected strain of Aedes aegypti mosquitoes was studied by histological means. About 75–80% of B. malayi died in the course of development, the peak death rate occurring about 2–3 days after the infecting meal. A majority of B. pahangi larvae survived to the 3rd-stage, but there were some deaths at all stages of development and also a few amongst haemocoele larvae.

The non-specific nature of the response of mosquito flight muscle to filarial parasitization

The significance of the histological changes induced by filarial larvae in the indirect flight muscle fibres of susceptible female mosquitoes was investigated by inflicting mechanical (needle-puncture) injury on thoracic tissues of male and female mosquitoes of various species. Mechanical injury caused the flight muscle of all mosquitoes, irrespective of species, sex or filarial susceptibility, to react in the same way as that of filaria-infected, susceptible females; other thoracic tissues responded in a similar fashion. Since these responses are closely akin to those observed by earlier authors in various tissues of other insects subjected to experimental trauma, it seems reasonable to regard the reactions of indirect flight muscle of mosquitoes to filarial larvae as an example of a common, non-specific response by insects to a range of traumatic stimuli.

Species variation in mosquito flight-muscle damage resulting from a single filarial infection and its repercussions on a second infection.

Serial sections of females of two highly filariasusceptible mosquitoes,Aedes togoi andAe. aegypti, were examined by light microscopy. Following a singleBrugia pahangi infection, the predominant reaction of flight muscles ofAe. aegypti was degeneration, whereas that inAe. togoi was nuclear enlargement, a putative repair response. This also holds true following mechanical injury (Beckett 1990), suggesting an inherent species difference in flight-muscle response to injury. The filariae of a secondB. pahangi infection, initiated after muscle damage had been established, usually avoid degenerate muscle fibres (which cannot support larval development) but entered similar proportions of normal fibres and those with enlarged nuclei. Filariae of a second infection, initiated whilst first-infection larvae were still within the muscle fibres, entered similar proportions of already-parasitized and non-parasitized fibres. The sole change in muscle fibres detectable by filarial larvae is therefore degeneration.

Peripheral cells in the salivary glands of female Aedes aegypti and A. togoi mosquitoes

Abstract A new type of cell, the peripheral cell, is described. These cells are located at the perimeter of the simple tubules which form the distal zones of the lateral lobes of the salivary glands of female Aedes aegypti and A. togoi. They may represent degenerate secretory cells which are segregated so that their altered secretory product cannot be discharged during blood feeding.

The distribution of developing Brugia pahangi and Brugia malayi larvae within the dorsal longitudinal flight muscles of Aedes aegypti and Mansonia uniformis

1. The distribution of larvae within the dorsal longitudinal muscle fibre groups of A. aegypti infected with subperiodic B. malayi or B. pahangi and of M. uniformis infected with the former parasite was studied with the aid of serial sections. 2. In all experiments the top bundles of fibres contained fewer parasites than either the middle or lowest bundles, but whereas most parasites were concentrated in the middle bundles in A. aegypti there was no significant difference in M. uniformis between the bottom and middle fibre bundles. The lowermost fibre was not the most heavily parasitized of the dorsal longitudinal group. 3. Nothing is known of what determines whether or not a particular fibre becomes parasitized, but it was concluded that the distance between the fibre and the gut (from which the parasites emerge to travel to the muscle) is not the principal factor. I am very much indebted to Mr Cheong Weng Hooi and his colleagues for collecting and processing mosquitoes in Kuala Lumpur and to Mrs J. Oliver who finished the processing in Liverpool. I am grateful also to Dr W. W. Macdonald for his advice and help in all stages of this work and to Miss M. A. Johnson who assisted with the care of the A. aegypti colony and prepared the diagrams for this paper.