Roger J. Wood

Acetylcholinesterase activity in organophosphorus and carbamate resistant and susceptible strains of the Culex pipiens complex

Abstract In vitro studies of acetylcholinesterase (AChE) activity and inhibition by insecticides have been carried out on larvae of four strains of mosquitoes of the Culex pipiens complex, two of which (MSE, DAR D ) were resistant to both carbamates and organophosphorus (OP) compounds, one (RANGOON) resistant only to OPs and the other (CfCA) susceptible to both. Activity of AChE in MSE was substantially lower than in CfCA and DAR >D while in RANGOON it was intermediate. The AChE of MSE was much less sensitive than other strains to inhibition by the carbamates propoxur and carbaryl and the OPs paraoxon and fenthion (I50 ratios with CfCa: >1250, >500, >10000, >11.1). Resistance to propoxur in MSE and DAR D was high (LC50 ratios with CfCa: MSE >667; DAR D = 2133 ) but resistance in both strains was unstable and declined when laboratory selection was relaxed. It is concluded (a) that resistance to carbamates and OPs in larvae of the MSE strain is associated with a mutant form of AChE of broad insensitivity, (b) that resistance to OPs in RANGOON is possibly associated with a change in AChE giving specific insensitivity to fenthion, and (c) that resistance to carbamates and OPs in DAR D is not explained by a change in AChE. The basis of resistance in these strains is discussed in relation to metabolic studies and the pattern of insecticide use in the field.

Selected lines of Aedes aegypti with persistently distorted sex ratios.

A breeding scheme to isolate X chromosomes sensitive to drive by the T8 (Trinidad) Y chromosome of Aedes aegypti (the MD haplotype) is reported. Crosses with an Australian strain Th.I (Thursday Island) revealed not only sensitive and resistant X chromosomes but also some with the capacity to drive against the T8 Y chromosome. Four strains were created in which sex ratio was male-distorted (28–36 per cent ♀) for 10 generations, with no regression towards sexual parity. The proportion of females varied significantly between generations in each of the four strains. Further selection produced strains with normal sex ratios, capable of generating fewer than 15 per cent ♀ on outcrossing to T8 males.

Effects of variations in a formulated protein meal on the fecundity and fertility of female mosquitoes

Abstract. A formulated protein meal developed by Kogan (1990) for adult female Aedes aegypti mosquitoes was evaluated and modified to increase egg and pupal yield. A vigorous laboratory colony was maintained with the females fed exclusively on this dietary formula for about twenty‐five generations over more than 2 years. Extra modifications were made to produce a diet suitable for Anopheles arabiensis and Anopheles stephensi females to produce eggs. Both formulations contain bovine albumin, haemoglobin and globulin in a ringer based solution, plus ATP as a phagostimulant for Ae.aegypti. Compared to Kogans original, our Aedes formula doubled the production of pupae per female after a single meal, although the yield was still significantly lower than from mosquitoes fed on animal hosts or defibrinated pig blood. In varying the proportions of different constituents during attempts to optimize the formula, no relationship was found between total protein content (within the range 80–220 mg/ml) and fecundity, percentage hatch or pupal yield of Ae.aegypti. Equivocal results were found when an isoleucine supplement was added to the formula.

A genetical study of DDT resistance in the mosquito Aedes aegypti.

SummaryCrosses have been carried out to determine the relationship between adult DDT resistance and the three linkage groups of the mosquito Aedes aegypti.Two linkage groups were implicated in the control of DDT resistance. In the Bangkok-HR strain resistance derived mainly from linkage group III, probably with the maor effect from the gene RDDT2. When resistance was transferred into a susceptible background, by outcrossing Bangkok-HR to strain 64 and reselecting, resistance in the resulting Bangkok-MR strain came from both linkage groups II and III.

Male biased sex ratio in the Mediterranean fruit fly Ceratitis capitata , an example of Y-chromosome meiotic drive

A case of Y-chromosome meiotic drive is reported in the Mediterranean fruit fly Ceratitis capitata. It arose in an irradiated male and results in excess of males. Male excess is inherited strictly from father to son. A Y-linked factor MP (male producer) is proposed. Higher drive can be selected, but distortion declines rapidly in the absence of selection. Hybrid males from crosses between driving males and nondriving females also show drive but to a reduced extent, suggesting the action of suppressors. Sex ratio distortion is independent of postzygotic mortality, and is not associated with an obvious chromosome arrangement. Spermiogenesis in driving males is characterised by abnormalities in sperm tails and reduced numbers in some sperm cysts, whereas neighbouring cysts of the same MP testis are essentially wild type. The average number of missing sperms plus deformed sperms approximates to the average depression in female recovery among the progenies of siblings, suggesting that most of the missing or abnormal sperms would have given rise to females, that is, they would have been X-bearing. To explain the heterogeneity between neighbouring cysts, a theory is proposed that links it to variation in X-chromosome sensitivity to MP, arising by random suppression of the genetic basis of sensitivity during the six mitotic divisions in the origin of the cyst from its stem cell before meiosis.

Variation in Y chromosome meiotic drive in Aedes aegypti (Diptera : Culicidae) : a potential genetic approach to mosquito control

Reciprocal crosses between strains of Aedes aegypti (Linnaeus) from different geographical areas have revealed an unexpectedly complex pattern of holandrically inherited male biased sex ratios in F2. The variation has been interpreted in terms of a web of X–Y interactions in Fl, in which the Y chromosome may or may not show meiotic drive against the X chromosome with which it is paired. The pattern of inheritance is not in agreement with a single form of Y chromosome, driving with different degrees of intensity against Xs of different sensitivity, but indicates different forms of driving Y chromosome. A rule has emerged that if Fl males from any cross give rise to a male distorted sex ratio in their progeny (F2), the males from the reciprocal cross give rise to a normal sex ratio. All eleven newly colonized strains from Ghana showed Y meiotic drive against the Xs of five strains, one of American and four of Australian origin, although one of the eleven showed a greater degree of drive than the other ten against the same sensitive strains. The variation observed is discussed in relation to previous studies on meiotic drive by the MD haplotype, and to the possible exploitation of sex ratio distortion in controlling this potentially dangerous insect.

The effect of larval selection on adult resistance to DDT in two strains of the mosquito Aedes aegypti (L).

SummaryEvidence is presented which confirms the influence of linkage group II on adult DDT-resistance in one strain of Aedes aegypti (Bangkok-MR) but not in another strain (Bangkok-HR).