Host suitability of three Opuntia taxa for the Dactylopius opuntiae (Hemiptera: Dactylopiidae) 'stricta' lineage

Dactylopius opuntiae 'stricta' lineage was released more than 20 years ago in South Africa where it has successfully controlled Opuntia stricta. However, its host preference had not been tested against all invasive cacti in South Africa. Therefore, the possibility exists that it might successfully control other invasive cacti. We compared the performance of the 'stricta' lineage on Opuntia stricta, Opuntia humifusa and two lineages of Opuntia engelmannii. Additionally, we assessed if morphology of these Opuntia taxa could be used as an indicator of host selection by the 'stricta' lineage of D. opuntiae. Acceptability and suitability of the host taxa were measured by D. opuntiae life history parameters such as crawler development time and female weight. Principal component analysis of six morphometric characters of the Opuntia taxa was used to assess similarities between the taxa. Opuntia stricta is morphologically more similar to the O. engelmannii lineages than to O. humifusa, which showed little similarity to any of the other taxa. Additionally, the two O. engelmannii lineages showed some morphological similarity to each other. The 'stricta' lineage completed its development on O. humifusa such that the cochineal could be considered as a potential biological control agent for O. humifusa. Conversely, D. opuntiae 'stricta' was not able to complete development on O. engelmannii. Consequently, it would not be a suitable biological control agent for either lineage of O. engelmannii. The results show that O. humifusa is a suitable host for D. opuntiae 'stricta' and that Opuntia morphology is not an obvious indicator of host suitability.

Automated summary

The study found that the 'stricta' lineage of Dactylopius opuntiae could potentially be a biological control agent for Opuntia humifusa; morphology is not a clear indicator of host suitability.