Spatial trade-offs in the digestive and reproductive systems of grape phylloxera

Abstract

Trade-offs between reproduction and other energy-requiring activities are present in insects. However, feeding and reproduction are not often thought to be trade-offs, although in small insects space may be limiting for both ingestion of food and egg development. This study characterised the structure of the digestive system of radicicolae Daktulosphaira vitifoliae (Hemiptera: Phylloxeridae) to investigate how feeding and egg development occur in this species. Using light and electron microscopy, the midgut of D. vitifoliae was observed to be composed of anterior and posterior regions, separated by a hindgut connection. The midgut is compressed during the development of parthenogenetically produced eggs in adults; individual eggs are ∼30% of the adult length and in volume internally occupy 3-5% of the body cavity. The midgut posterior chamber is suggested to be essential for the continual supply of energy during periods of reduced food intake. The presence of the hindgut and an anal opening indicated that waste excretion through the anus was physiologically possible, although honeydew excretion was not observed. The structure of the digestive system of radicicolae D. vitifoliae is atypical, containing adaptations that may assist the survival of the monophagous insect during dispersal events to a new Vitis food source.