Synthetic sex pheromone attracts the leishmaniasis vector Lutzomyia longipalpis to experimental chicken sheds treated with insecticide

Abstract

Background: Current strategies for controlling American visceral leishmaniasis (AVL) have been unable to prevent the spread of the disease across Brazil. With no effective vaccine and culling of infected dogs an unpopular and unsuccessful alternative, new tools are urgently needed to manage populations of the sand fly vector, Lutzomyia longipalpis Lutz and Neiva (Diptera: Psychodidae). Here, we test two potential strategies for improving L. longipalpis control using the synthetic sand fly pheromone (+/-)-9-methylgermacrene-B: the first in conjunction with spraying of animal houses with insecticide, the second using coloured sticky traps.

Results: Addition of synthetic pheromone resulted in greater numbers of male and female sand flies being caught and killed at experimental chicken sheds sprayed with insecticide, compared to pheromone-less controls. Furthermore, a ten-fold increase in the amount of sex pheromone released from test sheds increased the number of females attracted and subsequently killed. Treating sheds with insecticide alone resulted in a significant decrease in numbers of males attracted to sheds (compared to pre-spraying levels), and a near significant decrease in numbers of females. However, this effect was reversed through addition of synthetic pheromone at the time of insecticide spraying, leading to an increase in number of flies attracted post-treatment.In field trials of commercially available different coloured sticky traps, yellow traps caught more males than blue traps when placed in chicken sheds. In addition, yellow traps fitted with 10 pheromone lures caught significantly more males than pheromone-less controls. However, while female sand flies showed a preference for both blue and yellow pheromone traps sticky traps over white traps in the laboratory, neither colour caught significant numbers of females in chicken sheds, either with or without pheromone.

Conclusions: We conclude that synthetic pheromone could currently be most effectively deployed for sand fly control through combination with existing insecticide spraying regimes. Development of a standalone pheromone trap remains a possibility, but such devices may require an additional attractive host odour component to be fully effective.

Figure 1

Sand flies attracted to insecticide-treated chicken sheds using synthetic pheromone. Number of sand flies (a. females; b. males; geometric means ± 95% CI) captured and killed at insecticide-treated chicken sheds, fitted with either pheromone dispensers (one or ten, white bars) or one control dispenser (no pheromone, grey bars). * P < 0.05, ** P < 0.01, *** P < 0.001.

Figure 2

Effect of pheromone on number of sand flies attracted to chicken sheds following insecticide treatment. Number of sand flies (a. females; b. males; geometric means ± 95% CI) captured at chicken sheds over two nights before (grey bars) and after (white bars) treatment with insecticide, applied either with or without synthetic pheromone. * P < 0.05, ** P < 0.01, *** P < 0.001.

Figure 3

Sand flies captured on sticky traps of different colours using synthetic pheromone. Number (geometric mean ± 95% CI) of female (grey bars) and male (white bars) sand flies caught in chicken sheds on blue and yellow sticky traps, with and without pheromone dispensers.