137 Twentieth Australasian Weeds Conference Summary Six biotypes of Dactylopius tomentosus (Lamarck) (Hemiptera: Dactylopiidae) have been imported into Australia as biological control agents to combat the eight naturalised invasive Cylindropuntia species. Each D. tomentosus biotype tested exhibited significant differences in host specificity, host pref- erence and performance across the Cylindropuntia species. Biocontrol success is dependent on the cor- rect identification of the targeted plant species and the correct matching of an insect or pathogen to that plant. An optimal release strategy is to match the most effective biotype to the targeted Cylindropuntia spe- cies. Biotype matching to Cylindropuntia species was enhanced through the use of molecular phylogenetic tools and more thorough morphological observations of the cacti species. Molecular studies demonstrated that using two plastid markers (Rpl36-Rps8 spacer region and TrnH-PsbA spacer) and a nuclear region (phosphoenolpyruvate carboxylase) allowed for differentiation of the eight Cylindropuntia species. Molecular analyses using three markers enable the identification of unknown Cylindropuntia species when species identification is not possible using tra- ditional phenological and morphological tools. The genetic identification of the Cylindropuntia provides a time efficient match of target host species and biotype within days rather than the traditional long term host trials (three month life cycle) previously required. Utilising DNA analyses will markedly improve the chance of containment of Cylindropuntia infestations in Australia through better matching of biocontrol agents with their most preferred host. Keywords Host specificity, biotypes, molecular analysis, biocontrol. INTRODUCTION The genus Cylindropuntia is native to southern USA and Mexico and comprises 33 species, eight of which have naturalised in Australia. These eight species: C. fulgida var. mamillata (DC.) Backeb., C. imbricata Improving the effectiveness of the release strategy for the array of Dactylopius tomentosus biotypes for the biocontrol of Cylindropuntia species by using DNA analysis Peter K. Jones 1 , Jane Oakey 2 , Michael D. Day 1 and Joseph S. Vitelli 1 1 Queensland Department of Agriculture and Fisheries, Ecosciences Precinct GPO Box 267, Brisbane, Queensland 4001, Australia 2 Queensland Department of Agriculture and Fisheries, Health and Food Sciences Precinct, Box 156, Archerfield BC, Queensland 4108, Australia (peter.jones@daff.qld.gov.au) (Haw.) F.M.Knuth, C. kleiniae (DC.) F.M.Knuth, C. leptocaulis (DC.) F.M.Knuth, C. prolifera (Engelm.) F.M.Knuth, C. rosea (DC.) Backeb., C. spinosior (Engelm.) F.M.Knuth and C. tunicata (Lehm.) F.M.Knuth are shrubs ranging in height from 60 cm to 3 m (Holtkamp 2012b, Botanic Gardens Trust 2013). These plants have succulent segments growing end- to-end that are armoured with large barbed spines and tiny bristles known as glochids. Collectively these weeds pose serious environmental, agricultural and recreational problems through restricting access to recreational areas, reduced productivity of agricultural land and injury to livestock and native animals. Variation within species has been a major obstacle for correct identification and the wide variability in morphological traits is increased by environmental conditions that ultimately influence the growth habit of the plants – leading to confusion in correct identi- fication of some species. Two cochineal insects, Dactylopius tomentosus ‘imbricata’ biotype and D. tomentosus ‘cholla’ bio- type have been released to control C. imbricata and C. fulgida respectively. There are another four D. tomentosus biotypes in quarantine awaiting approval for field release. These six biotypes collectively at- tack the majority of Cylindropuntia species found in Australia. However, they all show a significant differ- ence in performance and preference between the eight Cylindropuntia species. Successful biological control of these Cylindrop- untia species is dependent on releasing the most effec- tive biotype to control each individual Cylindropuntia species. Ultimately, the success of the release strategy is thus dependent on the correct identification of the infestation species. This paper describes the molecular techniques on how to distinguish the eight naturalized Cylindro- puntia species in Australia and the impact this has on the future success of the Cylindropuntia biological control program.