PARASITOIDS
In a study in KwaZulu-Natal, South Africa high levels of parasitism of
Busseola fusca pupae by the parasitoid Procerochasmias
nigromaculatus (Cameron) (Ichneumonidae) were recorded. Up to 100%
parasitism was recorded in the middle of the growing season, during
February-March, and 80% during November, when borer larvae which had terminated
diapause were parasitised after pupation. Larval parasitism mainly by
Cotesia sesamiae, which was reared from about 87% of parasitised
larvae, peaked at 75% during January. Despite the high parasitism levels by
these parasitoids they did not prevent economically significant damage.
In addition the following parasitoids were also recorded from Busseola fusca
in South Africa: the egg parasitoids Telenomus busseolae Gahan
(Scelionidae) and Trichogrammatoidea lutea Girault (Trichogrammatidae);
the larval parasitoids Aleiodes sp. (Braconidae), Bracon
sesamiae Cameron (Braconidae), Chelonus curvimaculatus Cameron
(Braconidae), Stenobracon (=Euvipio) sp. (Braconidae),
Glyptapanteles maculitarsis (Cameron) (Braconidae), Habrobracon
brevicornis (Wesmael) (Braconidae), Iphiaulax sp. (Braconidae),
Palexorista sp. (Tachinidae), Paradrino halli Curran
(Tachinidae), Sarcophaga sp. (Sarcophagidae), Temelucha sp.
(Ichneumonidae) and Odontepyris transvaalensis (De Buysson)
(Bethylidae); the pupal parasitoid Pediobius furvus Gahan (Eulophidae),
and the hyperparasitoids Aphanogmus fijiensis (Ferrière)
(Ceraphronidae) which attacks C. sesamiae cocoons, and Eurytoma
braconidis Ferrière (Eurytomidae) which attacks Stenobracon sp.
and H. brevicornis.
In the North-West Province of South Africa, peaks of up to 100% parasitism
were recorded on Chilo partellus pupae every year in several
consecutive growing seasons during the second part of January and the first part
of February. The most abundant pupal parasitoids were the solitary
Dentichasmias busseolae and the gregarious Pediobius furvus.
Occasionally, Conomorium sp. (Pteromalidae), was also reared from
field-collected pupae of Chilo partellus. Larval parasitoids were
active throughout the growing season on maize and grain sorghum. Parasitism
oscillated around 10% with occasional peaks of 20-30%. The most abundant larval
parasitoid of Chilo partellus was Cotesia sesamiae. This parasitoid was
active throughout the season and was reared from about 93% of all parasitised
larvae. The hyperparasitoid, Aphanogmus fijiensis, was frequently
reared from field-collected Cotesia sesamiae cocoons, sometimes
reaching 50-100% parasitism in autumn. Other larval parasitoids that attacked
C. partellus were Iphiaulax sp., the egg-larval parasitoids,
Chelonus curvimaculatus, and Chelonus sp., Bracon
sp., Norbanus sp. (Pteromalidae), Pristomerus sp.
(Ichneumonidae) and Palexorista sp. (Tachinidae) The hyperparasite,
Eurytoma sp., was reared from field collected cocoons of
Iphiaulax sp. on several occasions. During winter, parasitism of
diapausing C. partellus larvae was very low. Two parasitoids, C.
sesamiae and Bracon sp. were observed to be active during winter.
Three parasitoids, Chelonus curvimaculatus, Chelonus sp. and
Pristomerus sp. diapaused in synchrony inside the larvae, and Iphiaulax
sp. diapaused in its own cocoon inside the dry stalks.
All the above parasitoids are indigenous to Africa and their association with
the exotic C. partellus is relatively new. These parasitoids usually
develop on other indigenous Lepidoptera and they moved from their indigenous
hosts to utilize C. partellus as a new alternative host. Although
larval and pupal parasitoids are playing an important role in reducing the
population levels of C. partellus, they are not able to reduce it to
below economic damage levels. The parasitoids could not prevent the dispersal
and subsequent wide distribution of C. partellus after its introduction
into Africa.
PREDATORS
The ant, Dorylus helvolus (L.) and the mouse, Mastomys natalensis
(Smith) were found to be the dominant predators of stem borers in maize and
grain sorghum in South Africa. Other predators in descending order of importance
were Cardiophorinae larvae, the doryline ant Aenictus sp.,
larvae of Astylus atromaculatus Bl. (Coleoptera: Melyridae),
tenebrionid larvae, larvae and adults of Heteronychus arator F.,
carabid larvae, staphylinids and Dermaptera.
PATHOGENS
Stem borer pathogens in southern Africa have received very little attention.
High winter mortality of hibernating B. fusca larvae was recorded. As
low activity by stem borer parasitoids was recorded in winter, this mortality
could be partially attributed to pathogens. A microsporidium, Nosema
partelli Walters & Kfir (Protozoa: Microsporidia: Nosematidae), was
recorded in C. partellus in South Africa. In addition, a recent survey
of pathogens conducted in South Africa revealed the following pathogens
identified from cadavers of B. fusca: cytoplasmic polyhedrosis virus,
granulosis virus, nuclear polyhedrosis virus, the entomopathogenic fungi
Beauveria bassiana (Balsamo) (Fungi imperfecti) and Entomophthora
sp. (Phycomycetes), the bacteria Serratia marcescens Bizio
(gram-negative facultative anaerobic pathogen, non-sporeformer) and Bacillus
thuringiensis Berliner (endospore-forming rods and cocci, obligate
pathogen), and the microsporidium Nosema sp. From cadavers of C.
partellus cytoplasmic polyhedrosis virus, entomopox virus, the fungi
Beauveria bassiana, Entomophthora sp. and Aspergillus sp.
(Fungi imperfecti) the bacteria Streptococcus sp. (gram-nagative
cocci), Serratia maecescens and Bacillus thuringiensis and the
microsporidium Nosema partelli were isolated.
