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POTENTIAL OF BEAUVERIA BASSIANA AND PAECILOMYCES
FUMOSOROSEUS (DEUTEROMYCOTINA: HYPHOMYCETES) AS BIOLOGICAL
CONTROL AGENTS OF THRIPS PALMI (THYSANOPTERA: THRIPIDAE)
A. Castineiras1, J. E. Peña1, R. Duncan1
and L. Osborne2
1Tropical Research and Education Center
2Central Florida Research and Education Center
The melon thrips, Thrips palmi Karny, is one of the
most important vegetable pests damaging pepper, eggplant, bean
and cucurbits in South Florida. Eggs are laid in the leaf tissue.
Life cycle consists of two aerial feeding stages and two subterranean
non-feeding stages. Adults emerge from the soil and move to the
leaves of the host plant (Walker 1992).
Literature on biological control of thrips is mostly
about predators (Riudavets 1995) and parasitoids (Loomans et al.
1995). There have been only a few reports on the efficacy of entomopathogenic
fungi. Neozygites parvispora (MacLeod & Carl) Rem. & Keel.
(Saito et al. 1989) and Verticillium lecanii (Zimm.) Viégas
(Saito 1992) have been documented infecting T. palmi in greenhouses
in Japan. Also, an unidentified species of the genus Hirsutella
Patouillard was found in Trinidad, British West Indies, infecting
approximately 80% of T. palmi populations in the field (Hall 1992).
To determine the potential of Beauveria bassiana
(Bals.) Vuill. and Paecilomyces fumosoroseus (Wize) as biological
control agents of T. palmi, strains BbH and BbHa of B. bassiana
and strain 97 of P. fumosoroseus (Table 1) were tested.
Beauveria bassiana and P. fumosoroseus inocula were
cultured on Dodine medium (Oatmeal agar plus 0.8 g dodine and
0.2 g tetracycline) and grown on rice in an incubator at 26 ±
1°C, 75-85% RH and a photoperiod of 12:12 (L:D).
Green bean plants (Phaseolus vulgaris L. cv. Opus)
were grown singly in pots in a greenhouse at 26 ± 2°C
and 80 ± 5% RH. When plants had 3 to 4 leaves, they were
inoculated with 50 T. palmi larvae taken from a laboratory colony.
Table 1. Strain origin of Beauveria bassiana and
Paecilomyces fumosoroseus tested on Thrips palmi.
Strains
Four groups of 10 infested bean plants were tested.
Three groups of plants were treated with the entomopathogenic
fungi, each one with a different strain, by spraying one ml of
conidial suspensions (2.0 × 108 conidia per ml) on each plant.
High conidial concentrations were used expecting a high mortality
on T. palmi. Conidial suspensions were obtained by washing 100
g of rice with mycelium in 400 ml of sterile 0.05% Tween 80 water
solution. One group of plants (control) was sprayed with sterile
0.05% Tween 80 water solution.
Plants were maintained in the same greenhouse and
conditions for 24 h, then one leaf of each plant was placed in
one 135 mm petri dish lined with moist filter paper. Plates were
sealed with parafilm and incubated for 72 h at 26 ± 1°C
and a photoperiod of 12:12 (L:D). Infection by the fungus was
confirmed by microscopic examination of mycelium visible externally
on the insect cuticle. Percent mortality was calculated. On the
same days infected larvae on incubated leaves were counted, a
sample of one leaf was taken from each plant in the greenhouse
and checked for infected thrips larvae. Data were analyzed using
Statistical Analysis System general linear models (SAS 1985) for
balanced ANOVA. Means were separated by a Waller-Duncan k-ratio
t-test.
No infected insects were found on the non-incubated
leaves taken from the greenhouse. On the incubated leaves, B.
bassiana BbHa caused the highest mortality but the percent of
infected larvae was rather low (Table 2). It has been documented
that a very high relative humidity (95%) is necessary for conidial
germination of entomopathogenic fungi (Ramoska 1984, Walstad et
al. 1970) and the average relative humidity in the greenhouse
was below 85%. P. fumosoroseus 97 was not a good candidate for
biological control of T. palmi because only a few insects (0.20%)
were infected by the fungus.
Because B. bassiana BbHa was the strain that induced
the highest mortality on the thrips in the previous experiment,
it was further tested in the soil.
Bean plants were grown on PRO-MIX BX® (Les Tourbières
Premier Ltée, Rivière-du-Loup, Québec, Canada)
potting soil (75-85% Canadian Sphagnum Peat Moss, pH=6.5) in 49×34×5
cm plastic flats in a greenhouse (26 ± 2°C and 80 ±
5% RH) until 3 to 4 leaves developed. Plants were infested by
placing bean leaves on top of them with T. palmi taken from a
bean field in Homestead, Florida. Potting soil was infested with
thrips pupae ten days later with plants that were cut and left
to dry on the flats. The dried plants were removed from the flats
4 days later.
Eight flats taken at random were sprayed with 100
ml of a spore suspension (3.1 × 108 spores per ml) obtained
as described before, and eight flats also taken at random (control),
were sprayed with 100 ml of sterile 0.05% Tween 80 water solution.
Mean temperature and relative saturation value of the soil (monitored
daily) were 22.6 ± 2°C and 47.5 ± 3% RS, respectively.
Table 2. Percent mortality of Thrips palmi larvae
treated with Beauveria bassiana and Paecilomyces fumosoroseus.
Entomopathogens
1Means followed by the same letter are not significantly
different according to a Waller-Duncan k-ratio t-test on arcsine
transformed data (p>0.001, k-ratio=100). Untransformed means
are presented.
Soil fungus concentration was determined 24 h after
treatment by taking 5 g soil samples from each flat. Samples were
suspended in 30 ml of sterile 0.05% Tween 80 water solution. Serial
suspensions (10-1 to 10-8) were plated on Dodine medium and incubated
as in the previous experiment. The number of colony forming units
(CFU) was determined after 6 days.
The effect of the pathogen on thrips survival was
evaluated by placing one ground emergence trap (Peña &
Duncan 1992) per flat and counting the number of emerging adults
at 3, 4, 6, 9, and 12 days after treatment. Traps consisted of
an opaque vinyl chloride pipe (20.5 cm diam, 15 cm high) covered
with a transparent plastic plate coated with Tanglefoot® (The
Tanglefoot Co.Grand Rapids, MI). New plates with Tanglefoot®
were placed on top of the pipes after each counting. Means were
separated using Statistical Analysis System t-test procedures
(SAS 1985).
Concentration of the fungus in the potting soil 24
h after spraying was 1.2 × 107 CFU per ml. The number of
adult thrips caught in the traps from sprayed flats was always
significantly lower than in control flats (Table 3). Emerging
adult thrips populations were 50.12%, 53.03% and 40.09% lower
in the treated flats on the third, fourth and sixth days after
spraying compared with the controls. Because all replicates were
conducted concurrently under the same conditions, and flats were
taken randomly, differences in adult emergence can be attributed
to the action of B. bassiana BbHa in the soil.
This study shows that there may be potential for
epizootics of B. bassiana in populations of T. palmi under certain
conditions. Beauveria bassiana is a soil fungus and soil provides
environmental conditions favorable to conidia (Gaugler et al.
1989). Because high aerial populations of the melon thrips are
related to low rainfall periods (Etienne et al. 1990, Cooper 1991)
and fungal pathogens need high relative humidity (Ramoska 1984,
Walstad et al. 1970), the soil inhabiting pupal stage seems to
be the most susceptible to fungal infection. However, much more
information is needed to determine the impact of entomopathogens
on pupal mortality, and on the frequency of pathogen inoculations
to effectively reduce T. palmi populations in the field.
Thanks to R. M. Baranowski (Tropical Research and
Education Center, University of Florida, Homestead, FL) and Roberto
Pereira (Dept. of Entomology and Nematology, University of Florida)
for reviews of the earlier version of this manuscript. This is
Florida Agricultural Experiment Station Journal No. R-04892.
Table 3. Cumulative number of adult Thrips palmi
emerged from flats treated with Beauveria bassiana BbHa and untreated
(control).
Emerged Adults ± S.E.1
Summary
The potential of Beauveria bassiana (strains BbH
and BbHa) and Paecilomyces fumosoroseus (strain 97) as biological
control agents of the melon thrips, Thrips palmi, was studied
in greenhouse experiments. Twenty-four percent mortality was found
on thrips larvae treated with B. bassiana BbHa but infection only
developed when leaves with larvae were incubated after being sprayed
with the pathogen. Mortality by P. fumosoroseus was very low (0.20%).
A reduction of 50% in adult emergence was observed when potting
soil with pupae was sprayed with B. bassiana BbHa.
References Cited
Cooper, B. 1991. Status of Thrips palmi (Karny) in
Trinidad. FAO Plant Protection Bulletin. 39: 45-46.
Etienne, J., J. Guyot, and X. Van Watermeulen. 1990.
Effect of insecticides, predation, and precipitation on populations
of Thrips palmi on aubergine (eggplant) in Guadeloupe. Florida
Entomol. 73: 339-343.
Gaugler, R., S. D. Costa, and J. Lashomb. 1989. Stability
and efficacy of Beauveria bassiana soil inoculations. Envirom.
Entomol. 18:412-417.
Hall, R. A. 1992. New pathogen on Thrips palmi in
Trinidad. Florida Entomol. 75: 380-383.
Loomans, A. J. M., and J. C. Van Lenteren. 1995.
Biological control of thrips pests: a review on thrips parasitoids.
Wageningen Agric. Univ. Papers. 95: 89-200.
Peña, J. E., and R. Duncan. 1992. Sampling
methods for Prodiplosis longifila (Diptera: Cecidomyiidae) in
limes. Envirom. Entomol. 21: 996-1001.
Ramoska, W. A. 1984. The influence of relative humidity
on Beauveria bassiana infectivity and replication in the chinch
bug, Blissus leucopterus. J. Invert. Pathol. 43: 389-394.
Riudavets, J. 1995. Predators of Frankiniella occidentals
(Perg.) and Thrips tabaci Lind.: a review. Wageningen Agric. Univ.
Papers. 95: 43-87.
Saito, T. 1992. Control of Thrips palmi and Bemisia
tabaci by a mycoinsecticidial preparation of Verticillium lecanii.
Proceedings of the Kanto Tosan Plant Protection Society. 39: 209-210.
Saito, T., T. Kubota, and S. Shimazu. 1989. A first
record of the entomopathogenic fungus, Neozygites parvispora (MacLeod
and Carl) Rem. and Kell., on Thrips palmi Karny (Thysanoptera:
Thripidae) in Japan. Appl. Entomol. and Zool. 24: 233-235.
SAS Institute, Inc. 1985. SAS User’s Guide: Statistics.
SAS Inst. Cary, N.C. 957 pp.
Walker, A. R. 1992. Biology and population ecology,
in D. J. Girling [ed.] Thrips palmi,a literature survey with an
annotated bibliography. International Institute of Biological
Control. Ascot, Berks, UK. 37 pp.
Walstad, J. D., R. F. Anderson, and W. J. Stambaugh.
1970. Effects of environmental conditions on two species of muscardine
fungi (Beauveria bassiana and Metarhizium anisopliae). J. Invert.
Pathol. 16: 221-226.
University of Florida, IFAS
18905 SW 280th St.
Homestead Florida 33031
University of Florida, IFAS
2807 Binion Road, Apopka 32703-9598
Isolated from
Locality
B. bassiana BbH
Cosmopoltes sordidus Germ. (Coleoptera: Curculionidae)
Homestead, Florida
B. bassiana BbHa
Bephrateloides cubensis (Ashm.)
(Hymenoptera: Eurytomidae)
Homestead, Florida
P. fumosoroseus 97
Mealybugs
(Homoptera: Pseudococcidae)
Apopka, Florida
% Mortality ± S.E1
B. bassiana BbHa
24.23 ± 0.84 a
B. bassiana BbH
12.90 ± 0.27 b
P. fumosoroseus 97
0.20 ± 0.02 c
Control
0.00 ± 0.00 c
Days after Treatment
Treated with B. bassiana BbHa
Untreated (Control)
t-value
(df =14)
Sig. level
3
97.87 ± 15.81
196.25 ± 15.81
2.28
P < 0.03
4
125.00 ± 20.15
266.50 ± 45.05
2.86
P < 0.01
6
254.62 ± 41.35
431.37 ± 53.16
2.62
P < 0.02
9
413.75 ± 48.14
587.75 ± 59.88
2.26
P < 0.04
12
429.62 ± 47.64
612.62 ± 63.27
2.31
P < 0.03