Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

EGYPT
ETHIOPIA
4.13 Ophiomyia phaseoli 245
The bean fly was first reported in 1922, together with a parasitoid, later
identified as Sphegigaster voltairei (= Trigonogastra agromyzae)
(Pteromalidae). The eurytomid Eurytoma larvicola was also recorded
(Hassan 1947). Later, Abul-Nasr and Assem (1968) recorded 5 parasitoid
species emerging from bean fly puparia in the laboratory (Table 4.13.1), but
no information was provided on their effectiveness.
O. phaseoli was first reported in the early 1970s from Phaseolus vulgaris
(French bean), Vigna unguiculata (cowpea) and soybean (Glycine max),
although economic damage occurred only on French bean. The leguminous
bush, Crotalaria laburnifolia was the only wild host which supported bean
fly and its 17 species of parasitoids throughout the year (Table 4.13.1). Of
these parasitoids, the pteromalids Sphegigaster stepicola and
S. brunneicornis were the commonest species, accounting for up to 44.5%
(average 26.2%) of total parasitisation on Crotalaria. Parasitisation by the
braconid Opius phaseoli averaged a low 5.6% (range 0% to 23.2%) on
Crotalaria, but it was the major parasitoid on French bean, accounting for
over 87% of the total parasitisation. Abate (1991) concluded from this that
the host plant plays an important role in Ophiomyia phaseoli population
dynamics, although it remains to be shown whether this applies equally to
the range of food legumes. It is, perhaps, relevant that the bean fly acts as a
true leaf miner on Crotalaria, the larvae mining and eventually pupating
within the leaf. This behaviour renders both stages more accessible to
smaller parasitoids than when larvae are in the deeper tissues of a bean stem.
The remaining 14 parasitoids recorded from Ethiopia (Table 4.13.1) were
classified as very rare, (defined by Abate (1991) as equal to or less than 10%
of total insect emergence) and together on average caused 9.6% mortality.
Observations suggested that mortality of French bean seedlings caused by
bean fly was much less severe in areas where the wild host, Crotalaria,
occurred (14.8% in 1987 and 3.8% in 1988) than in its absence (39.1% in
1987 and 36.1% in 1988 (Abate 1991)). This is circumstantial evidence that
natural enemies play an important part in regulating bean fly populations.
Negasi and Abate (1986) recorded a pteromalid Cyrtogaster sp. from
O. phaseoli on French beans but, as this was not mentioned in the later, much
more detailed paper on parasitoids by Abate (1991), it has not been included
in Table 4.13.1.