THE INCIDENCE OF PARASITISM IN TRICHILOGASTER-ACACIAELONGIFOLIAE (FROGGATT) (HYMENOPTERA, PTEROMALIDAE), A GALL-FORMING BIOLOGICAL-CONTROL AGENT OF ACACIA-LONGIFOLIA (ANDR) WILLD (FABACEAE) IN SOUTH-AFRICA
Fs. Manongi et Jh. Hoffmann, THE INCIDENCE OF PARASITISM IN TRICHILOGASTER-ACACIAELONGIFOLIAE (FROGGATT) (HYMENOPTERA, PTEROMALIDAE), A GALL-FORMING BIOLOGICAL-CONTROL AGENT OF ACACIA-LONGIFOLIA (ANDR) WILLD (FABACEAE) IN SOUTH-AFRICA, African entomology, 3(2), 1995, pp. 147-151
Native parasitoid species became associated with the galls of Trichilo
gaster acacinelongifoliae (Froggatt) within two years of its deliberat
e introduction into South Africa during 1982 for biological control of
Acacia longifolia (Andr.) Willd., a perennial, leguminous shrubby wee
d from Australia. Emergence of adult parasitoids from galls collected
during the 1994 austral summer indicated that levels of parasitism wer
e low (0.6 %) and had not increased from previous years. Inspections o
f immature T. acaciaelongifoliae within galls showed that the incidenc
e of parasitism was much higher (8.6 %) than was deduced from adult em
ergence. Levels of parasitism varied from 0 % to 21.3 % at four differ
ent localities. Most parasitoids were found in chambers located close
to the surface of the gall, irrespective of gall size or the numbers o
f chambers per gall, and only a small proportion of the occupants of d
eep-seated chambers were parasitized. There were no parasitoids in the
galls until late-November by which time adult emergence of T. acaciae
longifoliae was well advanced. Consequently, T. acaciaelongifoliae is
protected, both by its physical position and by its asynchronized phen
ology, from the generalist parasitoids it has acquired, and the wasp p
ersists as an important biological control agent of A. longifolia in S
outh Africa.