Impact of salivary gland hypertrophy virus infection on the mating success of male Glossina pallidipes: consequences for the sterile insect technique.

Many species of tsetse flies are infected by a virus (GpSGHV) that causes salivary gland hypertrophy (SGH). Female Glossina pallidipes (Austen) with SGH symptoms (SGH+) have reduced fecundity and SGH+ male G. pallidipes are unable to inseminate female flies. Consequently, G. pallidipes laboratory colonies with a high prevalence of SGH have been difficult to maintain and have collapsed on several occasions. To assess the potential impact of the release of SGH+ sterile male G. pallidipes on the efficacy of an integrated control programme with a sterile insect technique (SIT) component, we examined the mating efficiency and behaviour of male G. pallidipes in field cages in relation to SGH prevalence. The results showed in a field cage setting a significantly reduced mating frequency of 19% for a male G. pallidipes population with a high prevalence of SGH (83%) compared to 38% for a male population with a low prevalence of SGH (7%). Premating period and mating duration did not vary significantly with SGH status. A high percentage (>80%) of females that had mated with SGH+ males had empty spermathecae. The remating frequency of female G. pallidipes was very low irrespective of the SGH status of the males in the first mating. These results indicate that a high prevalence of SGH+ in G. pallidipes not only affects colony stability and performance but, in view of their reduced mating propensity and competitiveness, releasing SGH+ sterile male G. pallidipes will reduce the efficiency of a sterile male release programme

The mating duration and period before mating in minutes for SGH+ and SGH− male <i>G. pallidipes</i> in a field cage.

<p><b>A:</b> Females mated with SGH− males and remated with low SGH prevelance group, <b>B:</b> Females mated with SGH+ males and remated with low SGH prevelance group, and <b>C:</b> Females mated with SGH-males and remated with high SGH prevelance group.</p><p>Data are presented as detransformed mean values (in bold) and 95% confidence interval.</p><p>Mean values in the same column followed by the same letter do not differ at the 5% level. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042188#s3" target="_blank">Results</a> section for full statistical analysis.</p

Mating frequency by SGH status in field cage mating experiments.

<p><b>A:</b> Females mated with SGH− males and remated with low SGH prevelance group, <b>B:</b> Females mated with SGH+ males and remated with low SGH prevelance group, and <b>C:</b> Females mated with SGH-males and remated with high SGH prevelance group. Data are presented as mean values ± standard deviation.</p>**<p>mating frequency differs between SGH+ and SGH− males in the same row at the 1% level. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042188#s3" target="_blank">Results</a> section for full statistical analysis.</p

Impact of male SGH status on insemination rate (spermathecal fill) in <i>G. pallidipes</i> mated females.

<p>Impact of male SGH status on insemination rate (spermathecal fill) in <i>G. pallidipes</i> mated females.</p

Schematic representation of the design of experiments A, B and C (minimum competition) and D (direct competition).

<p>Schematic representation of the design of experiments A, B and C (minimum competition) and D (direct competition).</p

Mating percentage of SGH− and SGH+ males in the first and second matings.

<p>Numbers above columns indicate number mating and total number of males in category.</p

Impact of first and second mating combinations on the mating percentage in the second mating of <i>G. pallidipes</i>.

<p>A, Females mated with SGH− males and remated with SGH− males, B, Females mated with SGH+ males and remated with SGH− males, and C, Females mated with SGH− males and remated with SGH+ males.</p