Stem borers were monitored at Cedara (KwaZulu-Natal Province), Delmas (Mpumalanga Province) and Brits (North-West Province), South Africa. Moth populations of Busseola fusca were monitored with synthetic sex pheromone traps, while larval populations of the two stem borer species were monitored by scouting maize and grain sorghum fields. It was determined that Chilo partellus, which invaded Africa from India in the 1930’s, is expanding its distribution into the high elevations of the eastern Highveld region of South Africa, displacing the local B. fusca. Natural enemies (parasitoids, predators and microbial pathogens) were identified and their relative abundance and seasonal occurrence determined in the following provinces.

  • KWAZULU-NATAL
  • MPUMALANGA PROVINCE
  • NORTH-WEST PROVINCE

MONITORING OF BUSSEOLA FUSCA AND ITS NATURAL ENEMIES IN KWAZULU-NATAL PROVINCE

Moth flights of the stem borer Busseola fusca (Fuller) were monitored with synthetic sex pheromone traps during 1985-86 to 1990-91 (five growing seasons) in the KwaZulu-Natal Province, South Africa. Changes in larvae, pupae and parasitoid populations were monitored continuously on grain sorghum and ratoon crops during 1988-89 and 1989-90 (two growing seasons and a winter).

Two peaks of moth flights occurred every year. The first flight, which resulted from moths emerging from hibernating borers, peaked around the middle of November, and the second flight, usually larger, peaked at the end of February. B. fusca completed two generations on grain sorghum at Cedara. The first generation, which infested the early plants of the ratoon, peaked in the middle of January and the second generation peaked on the crops at the beginning of April. The fluctuation of borer numbers in the crops was synchronized with the instar distribution. An increase in the proportion of young larvae resulted in an increase in larval population, whereas an increase in the proportion of pupae resulted in a decline.

Pupal parasitism by Procerochasmias nigromaculatus peaked at 100% during February-March and coincided with a general decline in the population and a high proportion of pupae. Larval parasitoids were active from January to the end of May, peaking at 75% on the ratoon during January. Peaks of larval parasitism usually lagged behind the peaks of larval population and occurred when populations started to decline. The most abundant larval parasitoid was Cotesia sesamiae, which was reared from about 87% of parasitised larvae.

For more detail see:

Kfir, R. & Bell, R. 1993. Intraseasonal changes in populations of the African stem borer Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and its parasitoids in Natal, South Africa. Journal of African Zoology 107: 534-553.

MONITORING OF BUSSEOLA FUSCA AND THEIR NATURAL ENEMIES IN THE HIGHVELD REGION OF MPUMALANGA PROVINCE

Stem borers were also monitored in maize and grain sorghum fields near Delmas in the Highveld Region of Mpumalanga Province, South Africa from 1986-87 to 1992-93. Infestation of maize and sorghum by larvae and pupae of Busseola fusca peaked from February to April, then declined rapidly when the crops matured around May. Larvae that infested the crops during January and February diapaused in winter as mature larvae, pupated by October and emerged as moths during October and November.

Timing of male moth flights of B. fusca, determined with synthetic sex pheromone traps, was consistent, with three peaks occurring every year. The first flight, which resulted from moths emerging from pupae from larvae hibernating in spring, peaked around the middle of November, while the second and the third flights peaked around the middle of February and April respectively.

Larval parasitoids were active from February to May, with parasitism peaking at 40% at the end of the growing season in May. Peaks of larval parasitism lagged about four weeks behind peaks of larval populations and occurred when populations were declining. The most abundant larval parasitoid of B. fusca was Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) which was active throughout the growing season and in spring. Pupal parasitoids were abundant only during the 1989-90 growing season, peaking at around 50% parasitism during October.

The most abundant pathogen of B. fusca was the nucleopolyhedrosis virus (NPV) which occurred throughout the growing season and in winter, and caused mortalities during March to May that coincided with peak larval populations. Larval parasitoids, especially C. sesamiae, and microbial pathogens, especially NPV, were the major cause in the autumn decline of the larval populations of B. fusca.

For more detail see:

Kfir, R. 2000. Seasonal occurrence, parasitoids and pathogens of the African stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), on cereal crops in South Africa. African Entomology 8:1-14.

MONITORING OF CHILO PARTELLUS AND ITS NATURAL ENEMIES IN NORTH-WEST PROVINCE

The seasonal abundance of Chilo partellus (Swinhoe), and its parasites was studied at Brits in maize and grain sorghum from 1985 to 1989, and from 1985 to 1986 at Warmbaths, South Africa. C. partellus generations overlapped, and all development stages were present throughout most of the summer (November - March). The borer completed two and a half generations per season. The first generation occurred during October-November, infesting only early grain sorghum tillers from a ratoon crop. C. partellus produced an additional one and a half generations on the commercial crops that emerged later. In March-April, fifth and sixth instars of the third generation entered diapause in the dry stalks. During the second part of August, the larvae started to emerge from diapause and all had pupated or emerged as adults by October-November. Diapausing larvae were present during most of the year. An increase in the proportion of young larvae indicated an increase in the population, and an increase in the proportion of pupae indicated a decline. Infestation by borers started on the funnel leaves and then moved down in the stalks as the season progressed. The majority of winter larvae diapaused in the lower parts of stalks.

Pupal parasitism generally peaked at 100% and this corresponded with a decline of the first-generation larvae. The most abundant pupal parasites were Dentichasmias busseolae Heinrich at Brits, and Pediobius furvus (Gahan) at Warmbaths. Larval parasitism lagged behind peak larval populations and peaked at 80% parasitism. The most abundant larval parasite of C. partellus was Cotesia sesamiae (Cameron). Most recorded parasites are indigenous to Africa and their association with the exotic C. partellus is relatively new. Although they reduced densities of C. partellus, parasites did not reduce densities below economic damage levels.

For more detail see:

Kfir, R. 1992. Seasonal abundance of the stem borer Chilo partellus (Lepidoptera: Pyralidae) and its parasites on summer grain crops. Journal of Economic Entomology 85: 518-529.