Optimising control of invasive cactus using biological control

Abstract

Invasive opuntioid cacti pose significant impacts to the environment, agriculture, and recreation in Australia. The cochineal insects, Dactylopius spp., are effective biological control agents for a number of invasive cacti species in Australia, e.g., Dactylopius opuntiae ‘US’ lineage on Opuntia stricta, D. opuntiae ‘Mexico’ lineage on O. robusta, D. ceylonicus on O. monacantha, and D. austrinus on O. aurantiaca. Studies have found that these agents might also be suitable for control of some emerging invasive cacti. Dactylopius austrinus and D. ceylonicus have relatively narrow host ranges, whereas both D. opuntiae lineages feed and develop on a wider number of cactus species. Routine post-release field surveys of D. opuntiae lineages on O. tomentosa revealed biotic interactions that provide potential explanations for why the cochineal is generally not as effective on larger tree-form cacti. The presence of a predatory ant, Crematogaster spp., was often associated with poor establishment and low population build-up of the cochineal. Other significant predators include the “mealybug destroyer” Cryptolaemus montrouzieri and several Neuropteran species. The cactus longhorn beetle, Lagocheirus funestus, was rediscovered at one field site where it was observed causing significant damage to O. tomentosa. The rediscovery of this agent and its observed impact in the field, suggests its rearing and redistribution could complement cochineal biological control of O. tomentosa.