PEST RISK ANALYSIS (PRA) TRAINING Group Exercises Manual

PEST RISK ANALYSIS TRAINING - GROUP EXERCISES MANUAL APPENDIX 8
156 African Entomology Vol. 9, No. 2, 2001
Frankliniella occidentalis was collected for the
first time on mango flowers in this study (Table
1). Although found at Letsitele, this species may
expand its range as it was introduced during the
1980s (Giliomee 1989). This species is highly
polyphagous, having been recorded on numerous
hosts (Brodsgaard 1989; Mound 1997). In Israel,
where serious damage is inflicted on mango fruit,
very large numbers of F. occidentalis were
present on the inflorescences (Ben-Dov et al.
1992; Wysoki et al. 1993). Such numbers have
never been observed in South Africa and it
remains to be seen whether or not this species can
inflict the levels of damage observed in Israel.
Frankliniella schultzei (Trybom), known as the
common flower thrips, occurred at four localities
(Table 1). This polyphagous and flower-living
species has a worldwide distribution and can
damage young leaves within the bud (Mound
1997). It is known to carry spores of mildews,
moulds and rusts from infected plants and is also a
vector of tomato spotted wilt virus (Ullman et al.
1997). Frankliniella schultzei also occurs in citrus
flowers in South Africa but does not cause
damage (M.J. Gilbert, pers. comm.).
Hydatothrips adolfifriderici (Karny) was only
collected on one occasion (Table 1). It is known to
occur on a wide range of host plants, including
legumes (Zur Strassen 1960; Mound 1997).
Megalurothrips sjostedti (Trybom) was collected
from mango flowers at four localities (Table 1).
This species is known as the bean thrips in Africa
and is a major pest of cowpeas, where mechanical
damage to flowers may result in yield loss
(Alghali 1992). Ramaswamiahiella subnudula
Karny was collected from flowers at three
localities (Table 1).
Scirtothrips aurantii was collected from the
flowers, leaves and fruit and occurred at all
collecting sites (Table 1). This species was only
collected from new leaves and young fruit and it
seemed that feeding did not take place on mature
leaves and fruit. Both adults and larvae were
observed to cause lesions on the fruit, leaf
malformation and stunting of new growth. The
lesions on the fruit consisted of silvering and
cracking of the skin. The damage on the fruit was
only cosmetic and no harm was done to the fruit
flesh. Mango fruit with large lesions are not
suitable for export. According to the export
standards of the South African Mango Growers’
Association, lesions larger than 400 mm 2 for
count 7-14 and 500 mm 2 for count 4-6 fruit are
not acceptable for export. Criteria for the local
market are not as strict, but appearance of the fruit
affects its marketability. This species appeared to
be the most economically important thrips species
on mango and is also a well documented pest on
citrus in South Africa (Gilbert & Bedford 1998).
Selenothrips rubrocinctus fed on both young
and mature leaves and fruit but was not found in
the flowers (Table 1). Characteristically
associated with feeding damage on the fruit and
leaves were numerous small, shiny black spots of
excreta. Selenothrips rubrocinctus fed on both
sides of the leaves and caused rust-coloured
feeding scars as well as curled leaf edges. Greyish
lesions were caused on the mango fruit. Although
S. rubrocinctus can become a severe pest in young
mango plantings (Hill 1975), numbers in the
orchards were usually low and seemed to be under
good biological control. The phytoseiid mites,
Euseius sp. nr. rhusi, Iphiseius degenerans
(Berlese), Typhlodromus vescus Van der Merwe
and Euseius citri (Van der Merwe & Ryke) were
found in association with S. rubrocinctus and
seemed to regulate thrips numbers.
Taeniothrips gowdeyi (Bagnall) was found in
inflorescences at three sites (Table 1). It occurs
commonly within citrus flowers but its numbers
are low compared to Thrips tenellus Trybom
(Gilbert 1990). Thrips acaciae Trybom was
collected from flowers at two localities (Table 1)
and is also known to occur in the flowers of
Acacia karroo (Zur Strassen 1960). Thrips
tenellus was common in the mango flowers and
occurred at all the collecting sites (Table 1). It is
also commonly found in citrus flowers and in the
flowers of Acacia spp. (Gilbert 1990). Both T.
acaciae and T. tenellus probably feed on pollen.
Very high numbers of Thrips spp. were observed
in the flowers, but fruit abortion and yield loss did
not seem to be affected.
Aleurodothrips fasciapennis (Franklin), which
was collected from the leaves at two localities
(Table 1), is a predatory thrips that feeds on scale
insects (Palmer & Mound 1989). This species is
known to prey on the mango scale Aulacaspis
tubercularis Newstead in South Africa
(Labuschagne 1993).
Apart from thrips, there was a large complex of
other insects and mites present in the flowers. The
most noteworthy of these were Orius spp.
(Anthocoridae), which were commonly found
preying on thrips in the flowers.
Many species of thrips are known to transmit
fungi on their bodies by contact and movement.
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