Sugar feeding and fluid destination control in the phlebotomine sandfly Lutzomyia longipalpis (Diptera: Psychodidae)

Sandfly feeding behaviour and destination of coloured sugar meals in the gut of Lutzomyia longipalpis were investigated with particular attention to the role of the crop. Sandflies were able to ingest sugar from liquid drops, microcapillaries, a slice of pear and even sugar powder. In most cases the flies adopted a 'sugar feeding mode' with raised palps. As the fruit dried, flies of both sexes fed by piercing the tissue with the proboscis. All sugar-fed flies had a full crop plus a small amount of sugary fluid in the thoracic mid-gut, i.e. past the stomodaeal valve. Dissections of flies interrupted during feeding showed that the very first trace of sugar passed through the stomodaeal valve, but that the rest of the meal was diverted into the crop. This suggests that closure of the stomodaeal valve is initiated only after a small volume of sugar solution has passed through it.