Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

94 Biological Control of Insect Pests: Southeast Asian Prospects
fungi were capable of killing adults and larvae (Delattre and Jean-Bart 1978;
Filho et al. 1987; Busoli et al. 1989; Castineiras et al. 1991a,b; Pea and
Duncan 1991; Ponce et al. 1992; Brenes and Carballo 1994; Carballo and de
Lopez 1994; Pea et al. 1995). In the field the best results were obtained with
application of fungi twice a year at a dose of 10 13 conidia per ha. This
reduced trap catches of adults by 52% and rhizome damage by 65%, leading
to a 25% yield increase. Parallel experiments with 9 colonies per ha of the
predatory ant Pheidole megacephala yielded similar results (Castineiras et
al. 1991a,b).
Early laboratory tests in Guadelupe by Laumond et al. (1979) showed
that C. sordidus is susceptible to the entomopathogenic nematode
Steinernema carpocapsae (= S. feltiae), an observation since widely
confirmed in Central America for this and other nematode species (e.g.
Figueroa 1990; Pea and Duncan 1991). However, the most extensive recent
work has been carried out in Australia and Tonga. Twenty-one different
species of Steinernema and Heterorhabditis, 7 strains of Steinernema
carpocapsae, 2 of S. feltiae, 4 of H. bacteriophora and 2 of
H. zealandica were tested against adult banana weevils. The best of these,
S. carpocapsae BW strain, gave 85% infection in the laboratory (Parnitzki et
al. 1990, 1998; Treverrow et al. 1991). Adult C. sordidus are highly resistant
to entomopathogenic nematodes, due to the difficulty of nematodes entering
the host via the mouth or anus. The large spiracles of the first abdominal
segment offer an effective site of entry for the nematodes if they are able to
pass under the tightly fitting elytra. By adding paraffin oil to the nematode
preparation to seal the elytra, the beetle is caused to raise them slightly to
respire, simultaneously giving the nematodes access to the spiracles. Adult
weevils are strongly attracted to holes or cuts in the rhizome or psuedostem,
but they require a thigmotactic stimulus to remain long enough to become
infected by nematodes. If a core of tissue is removed from two sites at the
base of a residual corm using a desuckering tool, 250000 nematodes
(S. carpocapsae BW) added to each hole and the core loosely inserted,
nearly all adult weevils attracted are killed. In one large scale field trial in
New South Wales 8% of plants in untreated plots suffered significant
damage, 3% when prothiophos was added to the core, 1% when nematodes
were added and 0% when prothiophos was applied to the soil around the base
of the plant. It was concluded that control of banana weevil using
entomopathogenic nematodes should now be economically feasible
(Treverrow and Bedding 1992, 1993a,b). More recently, Treverrow (1994)
has found that baiting, and stem injection with very small amounts of
insecticide, can reduce treatment costs to less than 1 cent per stool. This
makes nematode applications against adults uncompetitive unless market