PEST RISK ANALYSIS (PRA) TRAINING Group Exercises Manual

PEST RISK ANALYSIS TRAINING - GROUP EXERCISES MANUAL APPENDIX 8
154 African Entomology Vol. 9, No. 2, 2001
cracking (Ben-Dov et al. 1992; Wysoki et al.
1993). F. occidentalis was first documented in
South Africa in 1987 and possibly entered the
country on cut flowers imported from Europe
(Giliomee 1989), but has not previously been
recorded from mango in South Africa. The castor
thrips, Retithrips syriacus (Mayet), is listed on
mango in Israel, but is not considered to be of
economic importance (Wysoki et al. 1993). This
species is known in South Africa from
Combretum zeyheri Sonder (Zur Strassen 1960).
Thrips hawaiiensis (Morgan) occurs on mango in
Thailand (Lee & Wen 1982), while Haplothrips
tenuipennis Bagnall and Thrips palmi Karny cause
damage to mango flowers in South Asia (Lewis
1997a).
The objective of this study was thus to identify
the Thysanoptera associated with mango trees in
South Africa and to make observations on the
abundance and importance of the different
species.
MATERIAL AND METHODS
Thrips survey
Thrips occurring on mango leaves, flowers and
fruit were collected from 1992 to 1996 in different
production areas of Mpumalanga (Friedenheim
(25°27'S 30°58'E), Kaapmuiden (25°26'S
31°30'E), Malelane (25°30'S, 31°14'E), Nelspruit
(25°26'S 30°58'E)) and the Northern Province
(Hoedspruit (24°30'S 31°10'E), Letsitele (23°48'S
30°25'E), Nondweni (23°05'S, 30°58'E)). Leaves,
flowers and fruit were examined and any thrips
present were removed with a fine brush.
Inflorescences were also shaken over a tray and
the thrips collected using an aspirator. The thrips
were stored in a mixture of nine parts 60 % ethyl
alcohol and one part acetic acid.
Monitoring thrips in the flowers and
on young fruit
To determine the diversity of thrips found in
mango flowers, flowers were sampled from
budding (August 1995) until the average fruit
length was 71 mm. This was done in a mango
orchard at the Institute for Tropical and
Subtropical Crops (ITSC) Nelspruit Experimental
Farm (25°26'S 30°58'E). This orchard consisted of
selected open-pollinated seedlings (the origin of
the pollen unknown). Inflorescences at the same
stage of development were marked and sampled
weekly by shaking five inflorescences over a tray
and collecting thrips with an aspirator. This was
ITSC Friedenheim Experimental Farm (25°27'S,
30°58'E) during 1996. In this case, ten
inflorescences were sampled from each cultivar.
Sampling commenced on 12 August 1996 and
was terminated on 7 October 1996 when the
average length of the Zill fruit was 9 mm and the
Sensation fruit was 19 mm.
Monitoring thrips with yellow card traps
In a Sensation orchard at the ITSC Nelspruit
Experimental Farm, three non-fluorescent yellow
polyvinyl chloride traps (140 × 76 × 0.2 mm)
were used for the monitoring of adult thrips from
August 1992 until March 1993. Traps were also
placed in a Zill orchard and a Fascell orchard at
the ITSC Friedenheim Experimental Farm from
August to November 1992. From September to
November 1996 traps were placed in a Zill and
Sensation orchard on the ITSC Friedenheim
Experimental Farm. Both sides of the traps were
coated with a sticky adhesive, Fly-tac®. Traps
were suspended 1.5 m to 2 m above the ground on
the northern side of the tree. The traps were
placed along a diagonal across the orchard with
one trap in the centre and the other two traps near
the opposing corners. Every week, traps were
removed and replaced. Removed traps were
covered with clear polyethylene plastic wrap.
Thrips were counted using a stereo-microscope.
Monitoring thrips with dispersal/emergence traps
Dispersal/emergence (D/E) traps sample
mature thrips larvae as they drop to the ground to
pupate, as well as adults emerging from the soil.
Each trap consisted of a square glass plate (250 ×
250 × 3 mm) placed on top of a polyvinyl chloride
irrigation pipe with a diameter of 130 mm and a
height of 100 mm. The glass plate was covered
with a sticky adhesive, Fly-tac®, and served as
the trapping surface. Larger D/E traps were used
by Reed & Rich (1975) and Tanigoshi & Moreno
(1981) for monitoring Scirtothrips citri (Moulton)
in citrus orchards in the U.S.A. and Gilbert (1992)
for monitoring S. aurantii in South African citrus
orchards. These traps were used for monitoring S.
aurantii and other thrips in a Zill and Sensation
orchard at the ITSC Friedenheim Experimental
Farm from 26 August to 4 November 1996. Three
traps per orchard were used and placed 300 mm
from the tree trunks (Reed & Rich 1975; Gilbert
1992). Traps were placed on the northern side. As
the traps prevented the larvae from reaching the
ground, it was necessary to change the position to
81