The host range of four new biotypes of <i>Dactylopius tomentosus</i> (Hemiptera: Dactylopiidae) from southern USA and their potential as biological control agents of <i>Cylindropuntia</i> spp<i>.</i> (Cactaceae) in Australia: Part II

Eight <i>Cylindropuntia</i> species have naturalised in Australia and pose serious economic, environmental and social impacts. The host range of four additional biotypes of <i>D. tomentosus</i> from southern USA was investigated. Feeding and development were restricted to the genus <i>Cylindropuntia</i>. However, they showed differences in specificity within this genus and some biotypes discriminated between the provenances of <i>Cylindropuntia rosea</i> and <i>Cylindropuntia tunicata</i>. Efficacy trials were conducted to determine whether populations of each biotype could be sustained on the naturalised <i>Cylindropuntia</i> species and if these populations could retard the growth or kill these plants. The ‘acanthocarpa’ biotype offers potential control of <i>C. rosea</i> (Lorne Station), while the ‘cylindropuntia sp.’ biotype shows great potential to control <i>C. rosea</i> (Grawin). The ‘cylindropuntia sp.’ biotype also had a high impact on <i>Cylindropuntia kleiniae</i> and <i>Cylindropuntia imbricata</i>, and a moderate impact on <i>Cylindropuntia leptocaulis</i> and <i>Cylindropuntia prolifera</i>. The ‘acanthocarpa × echinocarpa’ biotype had its greatest impact on <i>C. tunicata</i> (Grawin), killing this plant in 18 weeks. A fourth biotype, ‘leptocaulis’, was damaging to some species, but was less effective than the other biotypes. <i>Cylindropuntia spinosior</i> is the only naturalised species in Australia where no effective biocontrol agent has been found.