Genetic sex separation of the malaria vector, Anopheles arabiensis, by exposing eggs to dieldrin

Abstract

BackgroundThe sterile insect technique (SIT) has been used with success for suppressing or eliminating important insect pests of agricultural or veterinary importance. In order to develop SIT for mosquitoes, female elimination prior to release is essential as they are the disease-transmitting sex. A genetic sexing strain (GSS) of Anopheles arabiensis was created based on resistance to dieldrin, and methods of sex separation at the egg stage were developed. The use of this strain for SIT will require sexually sterile males: useful radiation doses for this purpose were determined for pupae and adults.MethodsFor the creation of the sexing strain, dieldrin-resistant males were irradiated with 40 Gy using a 60Co source and were subsequently crossed to homozygous susceptible virgin females. Individual families were screened for semi-sterility and for male resistance to dieldrin. For sex separation, eggs of a resulting GSS, ANO IPCL1, were exposed to varying concentrations of dieldrin for different durations. Percent hatch, larval survival, and male and female emergence were recorded. Radiation induced sterility was determined following adult and pupa exposure to gamma rays at 0–105 Gy. Mortality induced by dieldrin treatment, and levels of sterility post radiation were investigated.ResultsANO IPCL1 contains a complex chromosome aberration that pseudo-links the male-determining Y chromosome and dieldrin resistance, conferring high natural semi-sterility. Exposure of eggs to 2, 3, and 4 ppm dieldrin solutions resulted in complete female elimination without a significant decrease of male emergence compared to the controls. A dose of 75 Gy reduced the fertility to 3.8 and 6.9% when males were irradiated as pupae or adults respectively, but the proportions of progeny of these males reaching adulthood were 0.6 and 1.5% respectivelyConclusionThe GSS ANO IPCL1 was shown to be a suitable strain for further testing for SIT though high semi-sterility is a disadvantage for mass rearing.

The Anopheles arabiensis genetic sexing strain ANO IPCL1 and its application potential for the sterile insect technique in integrated vector management programmes

“…Although 99.94% of the females could be effectively eliminated by treating batches of up to 3000 eggs in 50 ml of 2-4 ppm dieldrin solutions for up to 6 h (Yamada et al, 2012), increasing the number of eggs to 10,000 resulted in a decline in efficacy and reliability. It has been necessary to add steps such as drying and de-clumping the egg masses prior to treatments, agitation of the solution for the movement of the eggs during treatment, and drastically increasing the volumes of the solution.…”

“…The GSS for A. arabiensis, 'ANO IPCL1' described here, was developed at the Insect Pest Control Laboratory (IPCL) of the Joint Food and Agriculture Organization (FAO)/International Atomic Energy Agency (IAEA) Agriculture & Biotechnology Laboratories using two pure-bred strains of A. arabiensis: the Sennar strain carrying the semi-dominant gene conferring resistance to dieldrin (Rdl), and the Dongola strain containing the dieldrin susceptible allele (Yamada et al, 2012). The resulting ANO IPCL1 strain showed no differences to the susceptible Dongola strain (the wildtype strain) in terms of life history traits, apart from a high natural semi-sterility of 73% .…”

Y-Linked Markers for Improved Population Control of the Tephritid Fruit Fly Pest, Anastrepha suspensa

“…In mosquitoes, similar GSSs have been developed since the 1970s based on dominant temperature sensitive (DTS) mutations [13] or insecticide resistance to dieldrin [5,6]. As with the tsl GSS, the mutations could be homozygous in both sexes, while only males carry the rescuing wild-type (WT) allele on the Y chromosome through an induced translocation.…”

“…For the most effective SIT programs, the species must be mass-reared, sexed early in development (separation of males and females), marked for monitoring, and sterilized by irradiation before release into affected areas. In particular, the production of a male-only population is highly important for large-scale SIT programs because this is most efficient and cost-effective for fruit fly programs [3,4] and a prerequisite for mosquito programs where adult females are vectors of disease [5,6]. For most biologically based control release programs, it is highly desirable to have females eliminated early in development to avoid female larval feeding in the mass rearing process [7].…”

Practical Applications of Insects' Sexual Development for Pest Control

“…These are based on translocation of a dominant selectable marker to the Y chromosome [Bailey et al, 1980;Hendrichs et al, 1995;Franz et al, 1997;Robinson et al, 1999;Robinson, 2002;Yamada et al, 2012]. However, these translocations are unstable resulting in labour intensive and costly massrearing systems, despite much effort to minimise the problem [Franz et al, 1994;Kerremans and Franz, 1995;Franz, 2005].…”