Host‐plant affinities of two biotypes of Dactylopius opuntiae (Homoptera: Dactylopiidae): enhanced prospects for biological control of Opuntia stricta (Cactaceae) in South Africa

Abstract

1. Until recently, neither the phycitid moth Cactoblastis cactorum nor the cochineal insect Dactylopius opuntiae have been satisfactory biological control agents of Opuntia stricta in South Africa. 2. In marked contrast, both of these agents have kept O. stricta under biological control for many decades in Australia. 3. In an attempt to improve the situation in South Africa, a stock of D. opuntiae was obtained from O. stricta in Australia during 1996. 4. Host‐specificity tests confirmed that the newly imported D. opuntiae from Australia is a different biotype to the one already established in South Africa. 5. The Australian (‘stricta’) biotype thrives on O. stricta but is unable to develop satisfactorily on O. ficus‐indica, while the converse is true for the South African (‘ficus’) biotype, which thrives on O. ficus‐indica but fares poorly on O. stricta. 6. The integrity of the host‐plant specificity of the two biotypes of D. opuntiae has important implications for biological control of Cactaceae in South Africa, and has greatly enhanced prospects that O. stricta can be brought under biological control successfully.

Biological control of cactus weeds: implications of hybridization between control agent biotypes

“…This paper reports on the results of the cross-breeding experiments. As such, it differs from the earlier studies of Githure, Zimmermann & Hoffmann (1999) and Volchansky, Hoffmann & Zimmermann (1999), which reported on the host-specificity of the true-bred 'ficus' and 'stricta' biotypes of D. opuntiae .…”

“…The dilemma was resolved recently when it was confirmed that D. opuntiae comprised at least two distinct biotypes, each specifically associated with a particular Opuntia species (Githure, Zimmermann & Hoffmann 1999;Volchansky, Hoffmann & Zimmermann 1999). Experiments showed that the biotype of D. opuntiae in South Africa, referred to as the 'ficus' biotype, favoured development on O. ficus-indica above O. stricta , while the one from Australia, referred to as the 'stricta' biotype, favoured development on O. stricta above O. ficus-indica.…”

Weed biological control in the European Union: from serendipity to strategy

“…It is unclear whether this is due to the differing period of residence of the insect or the humidity gradient. It is important to report that no non-target feeding has been observed despite intentional attempts to infect other Opuntia species in the field (V. Deltoro, unpublished data), as expected given the well-established host specificity of cactus-feeding Dactylopius species (Mann 1969;De Lotto 1974;Githure et al 1999;Volchansky et al 1999).…”

“…Haw. whereas the ficus biotype is associated with tree-like O. ficus-indica (Githure et al 1999;Volchansky et al 1999).…”

Distribution and socio-ecological impacts of the invasive alien cactus Opuntia stricta in eastern Africa

“…Another genotype of D. opuntiae, originally from Texas in the USA, was introduced to South Africa from Australia in 1997, where it had successfully controlled O. stricta and O. inermis (Dodd 1940;Hosking et al 1994). This genotype showed a strong preference for O. stricta Volchansky et al 1999). Its release in the KNP has resulted in a drop in the biomass of around 35 O. stricta cladodes/m 2 to under 5 cladodes/m 2 (Paterson et al 2011) and negated the need for physical and/or chemical control.…”