One of the significant factors causing seed mortality on the mother plant is pre-dispersal predation which has been intensively studied in many Asteraceae. Pre-dispersal predators could limit thistles propagation to new niches. Flower heads of thistles contain the most varied, specific and well-known insect fauna of any part of the plant. They present rich source of food, packed with achenes, and their inhabitants are protected from vertebrate predators by the tough spiny bracts.
Pre-dispersal predators are often considered as the first potential enemies in the generative reproduction of plant. The most known pre-dispersal predators used as biological control agents are classified into the weevils (Coleoptera: Curculionidae, especially Lixinae and Ceutorhynchinae) and tehpritids (Diptera: Tephritidae). Several of them are already used as successful biological control agents (Louda et al. 1997, Andreas et al. 2008, Van Driesche et al. 2008).
The most effective seem to be weevils (Curculionidae) (their larvae do not attack only seeds as Tephritidae or Tortricidae, but also the receptacle) and/or a combination of two and more bioagents which together create multiple stresses on the plant (e.g. Tephritidae + Tortricidae (sometimes + Curculionidae)).
Our study has focused on the occurrence and diversity of seed-feeding insects (pre-dispersal seed predators) in flower heads of over 30 Carduoideae species from Europe and North America, many of which are invasive in North America.
Anobiidae
Nitidulidae
Cecidomyiidae
Tortricidae
Chalcidoidea
Ichneumonoidea
Miridae
Tingidae