Published online by Cambridge University Press: 10 July 2009
Three species of Mesoclanis flies that attack the developing seeds of Chrysanthemoides monilifera in South Africa are being assessed for their potential as biological control agents of C. monilifera in Australia. Surveys in South Africa indicated that M. polana Munro is restricted to C. m. rotundata along the subtropical northern coast, M. magnipalpis Bezzi and M. dubia Walker occur on all three subspecies sampled (C. m. rotundata, C. m. monilifera, C. m. pisifera), although M. dubia is less abundant and has a more restricted distribution than M. magnipalpis. Mesoclanis eggs are laid into a wide range of flowerhead stages of C. m. rotundata over a period of approximately 12–14 days, from very small flowerheads with involucral bracts still completely closed, to flowerheads with the laminae of ray florets (petals) starting to elongate. Levels of oviposition by M. magnipalpis into C. m. pisifera are low in very young flowerheads, possibly as a consequence of a heavy layer of indumentum on young C. m. pisifera flowerheads. The pattern and location of feeding and pupation within flowerheads differs slightly for the three Mesoclanis species, but none of the species is associated with the formation of gall tissue. The effect of Mesoclanis activity on ovule development was assessed on four occasions. Mesoclanis destroyed all the ovules in some capitula, and the maximum level of ovule destruction recorded for a site was 64%.