Bip. Barratt et Pd. Johnstone, Factors affecting parasitism by Microctonus aethiopoides (Hymenoptera : Braconidae) and parasitoid development in natural and novel host species, B ENT RES, 91(4), 2001, pp. 245-253
A laboratory study of aspects of parasitoid host acceptance, suitability an
d physiological regulation in natural and novel host species was carried ou
t to investigate the degree of variability encountered with different hosts
and to determine the value of such observations in host range determinatio
n. The parasitoid Microctonus aethiopoides Loan was exposed to a natural ho
st, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) and three novel
hosts, the New Zealand native Nicaeana cervina Broun, the introduced weed
biological control agent Rhinocyllus conicus (Froehlich), and a congeneric
pest species, Sitona lepidus Gyllenhal (all Coleoptera: Curculionidae). Per
cent parasitism of these species was 54%, 43%, 39% and 0%, respectively. T
he results indicated that for both S. discoideus and R. conicus more males
than females were parasitized (69% cf. 45%, and 49% cf. 32% respectively) b
ut host size was not a significant factor. Overall, superparasitism was rec
orded in about 29% of parasitized weevils and there was evidence that host
discrimination to avoid superparasitism occurred in the natural host. Conve
rsely, superparasitism occurred more frequently than would be expected in N
. cervina (42%) coupled with higher survival of larvae in superparasitized
hosts in this species. The frequency distribution of attack of R. conicus b
y M. aethiopoides was not different from random. Parasitoid development was
more rapid in the natural host, S. discoideus, and parasitoid size was pos
itively correlated with host size. There was a strong positive relationship
between parasitoid larval survival and the presence of teratocytes in all
hosts. Host fecundity and fertility were reduced by parasitism for most spe
cies, and in some cases, by exposure to parasitoids in the absence of detec
table parasitism. It was concluded that laboratory observations can provide
useful information on the compatibility between host and parasitoid which
can complement traditional host range tests to predict field host range.