Reduction of Oriental Fruit Fly (Diptera: Tephritidae)
Populations in Papaya Orchards by
Field Sanitation l •2
Nicanor J. Liquido
Tropical Fruit and Vegetable Research Laboratory, USDA-ARS
Biocont.rol, Biology. Ecology, and Field Operations Research Unit
P. O. Box 4459, Hilo. Hawaii 96720
J. Agric. Entomol. 10(:1):163-170 (July 1993)
ABSTRACT The efTect offield sanitation in suppressing oriental fruit fly,
Dacus dorsalis Hendel, populations in 'Sunrise' pupaya (Cari.ca papaYfl L.)
orchards was dele.'mined by comparing larval density and percentage
infestation in mature green to fully ripe fruits sampled from fields with and
without cultural practice of sanitation. In addition, the relative density of
adults estimated using methyl eugenol-bailed traps was compared between
orchards with and without sanitation. Sanitation involved removal of ripe
fruits on trees and on the ground t ..... ice a week. The orcha,'ds without
sanitation had an irregular harvesting pattern which resulted in abundant
ripe fruits on trees and fallen, mtting fruits on the ground. Mature green
fruits had no oriental fruit fly infestation; infestntion was obsCl"V'cd only in
half- and fully·ripe fruits. Ol'iental fmit ny larval infestation (density and
percent infested fruit> was lower in half- and fully-ripe fruits collected from
the fields where sanitation was practiced. Likewise, the relativc density of
ol'icntal fruit ny adults was lower in the orchards with sanitation. Field
sanitation should, therefor'c, be an integral component of pest management
methods aimed at suppressing oriental fruit ny population in papaya
Ol"chards.
KEY WORDS
Insecta, Dipt.cra, Tcphritiduc, D(//:/l8, sanitation, suppression,
pest management.
-=--------------
Field sanitation is generally not practiced in commercial papaya (Carica
papaya L.) orchards in Hawaii. Ripe fruits and those with abnormal shapes and
sizes are removed from trees and left rotting on the ground. Adults of oriental
fruit Oy, Da.cus dorsalis Hendel, and melon Oy, Dacus cucurbitae Coquillett,
oviposit in and feed readily on the exudate of these fallen fruits (Liquido et al.
1989, Liquido 1991a,b). Liquido (unpublished dalal found that the juice exuding
from broken, ripe papaya fruit provides the nutrition necessary for normal
female egg production and longevity of both male and female adults. Liquido
(1991a) reported that fallen, ripe fruits on the ground serve as a reservoir of
resident melon fly populations in papaya orchards; melon Oy does
I
'J.
Received ror publication 2 November 1992; accepted 22 .Jonunry 1993.
This puper reports the results or research only. Mention or a proprietary product docs not constitute
an endorsement by USDA.
163
164
J. AgT1C. Entomol. Vol. 10, No.3 (993)
not normally infest papaya (McBride and Tanada 1949, Sea et aJ. 1982, Couey et al.
1984, Liquido et al. 1989, Liquido and Cunningham 1990, Liquido 1991b). In
addition, Liquido (1991a,c) found that fruits on the ground have higher oriental
fruit fly and melon fly larval densities than ripe fruits on trees. Therefore, a logical
deduction from these intensive field studies is that sanitation, i.e., removal of ripe
fruits on trees and on the ground, may be a valuable component of pest
management methods to suppress oriental fruit ny and melon fly infestations in
host commodities.
This paper reports on the effect of field sanitation in suppressing OI;cntal fruit
fly populations in 'Sunrise' papaya orchards on the island of Kauai. Hawaii.
Materials and Methods
Study site. The study was conducted in commercial ISunrisc' papaya orchards
on the windward side of the island of I(auai. These orchards were situated at
about 100 m elevation, with average monthly rainfall of 10-14 em, 16-2rC average
monthly minimum temperature, and 24-28°C average monthly maximum
temperature. Three I-ha fields with complete sanitation were selected as
treatment plots. Ripe fruits were regularly removed from trees and the ground
t\'nce a week in these plots. Likewise, three I-ha fields without field sanitation
were selected and designated as control plots. Plots without field sanitation had an
irregular harvesting pattern resulting in abundance of rotting fru.its on trees and
on the ground. Treatment and control plots were sun-ounded by tropical forest
with abundant wild guavas, Psidirtm guajaua L. and P. littoralle Radd.i, and
Eugenia spp., which are suitable hosts of oriental fruit fly.
Collection of fruit samples. Papaya fields were divided into equal quadrats
(15 m by 15 m). Twenty-five quadrats were randomly selected in both the
treatment and control plots. Trees at the middle of each quadrat were used as the
sampling points; each quadrat had 20-25 trees. Each sample tree was marked with
a flag tape, and farmers were requested not to harvest any fruit [Tom these trees.
One mature green, one half-ripe, and one fully-ripe fruit were collected from each
of the 25 sample trees per month. Sampling was done from May 1989 to August
1990.
Determination of oriental fruit fly density in fruits. The methods of
individual fruit holding, sifting of fruit and rearing medium for larvae and pupae,
and rearing of recovered larvae and pupae to adults followed the "emergence
method" described by Liquido et al. (1989). This method involved holding fruits
individually in plastic buckets (3.78 liters) that. contained a 5-cm layer of wheat
bran at the bottom. After 2 wk, pupating larvae and pupae were sifted from the
fruits and placed in a plastic container (0.25 liter) with sand for pupation. Adults
were allowed to emerge, then killed and preserved in alcohol for later
ident.ification and counting.
Adult trapping. The relative density of oriental fruit fly adults in t.he orchard
was surveyed using Morrocan traps (Hafraoui et al. 1980) with 2.5-cm cotton wick
impregnated with 2 ml of methyl eugenol (an oriental fruit fly male lure). Methyl
eugenol (Agrisense, Fresno, California) applied in cotton wicks contained 2% (by
volume) technical grade Naled (1,2-dibromo-2,2-dichloroethyl dimethyl phosphate
[A. H. Robins, Richmond, Va.]) as a toxicant. Three traps were installed 50 m
LIQUIDO: Suppression of Oriental Fruit Fly in Papaya
165
apart inside treatment and control plots. Trapping was done every 2 wk, with a 4-h
trapping duration (0800-1200 h) during each trapping occasion. Trapping was done
from September 1989 to August 1991.
The use of methyl eugenol-baited traps is a recognized reliable method of
estimating the relative abundance of oriental fruit fly populations (Harris et al.
1971, Vargas et al. 1983).
Analyses of data. Data were sorted and summarized by plot, ripeness index
and month of collection. The difference in mean oriental fruit fly larval density
per fruit and mean percentage fruit with larvae ~ 1 in half- and fully·ripe fruit
samples from fields with and without sanitation over time was determined by a
single-factor repeated measure analysis of variance (ANOVA). Sampling periods
(months) during which the fruit samples from both the sanitary and unsanitary
fields had zero infestation were not included in ANOVA (Steel and Tome 1980).
The variation in the relative density of oriental fruit fly adults caught in traps in
fields with and without sanitation was also determined by a single-factor repeated
measure ANOVA.
ANOVA by ripeness index was performed because it has been established that
oriental fruit fly infestation in 'Sunrise' papaya varies significantly with the degree
of fruit ripeness (Liquido 1991c). Before ANOVA, the number of oriental fruit fly in
fruits (lOglO[X + 1]) and traps (loglOx) were transformed to logarithmic values. The
percentage oriental fruit fly infestation in sample fruits was transformed to
arcsine values.
Statistical analyses were done using SAs/STAT Release 6.03 (SAS Institute
1988). Discussion by Collyer and Enns (1986) was used as the statistical reference.
Results
Mature green fruits had no oriental fruit fly infestation; infestation was
observed only in half- and fullYMripe fruits. Figs. 1 and 2 show the density and
percentage infestation of oriental fruit flies in half- and fully-ripe fruits,
respectively. Table 1 summarizes the results of repeated measures ANOVA
showing consistently (through time) significant variation in larval density and
percentage infestation of oriental fruit fly in half- and fully-ripe 'Sunrise' papayas
sampled from fields with and without cultural practice of sanitation. Half- and
fully-ripe fruits from clean, sanitary fields had 63% and 79% lower larval density,
respectively, than fruits of the same levels of maturity from dirty fields without
sanitation (Fig. 1). Similarly, the percentage oriental fruit fly infestation in half­
and fully-ripe fruits from sanitary fields was 84% and 83% lower, respectively,
than those from unsanitary fields (Fig. 2).
The relative density of oriental fruit fly male adults in sanitary and unsanitary
fields val;ed significantly, with the adult population being consistently less dense
in the field with sanitation (Table 1) (Fig. 3).
Discussion
Liquido (1991b) reported and discussed the density and percentage infestation
of oriental fruit fly in 'Sunrise' papaya, with appropriate emphasis on variation of
oriental fruit fly infestation due to the degree of fru.it ripeness and the absence of
J. Agric. Entomol. Vol. 10, No.3 (1993)
166
o
• Without sanitation
Wrth sanitation
6
Half ripe
OX = 0.33, SEM=0.21
• X" = 0.90, SEM=0.45
4
f­
-
2
o
.I
~ 35
.~ 30
o
c
.11
,
,
Fully ripe
OX= 2.70,SEM=1.12
• X=
m 25
"
,
12.62, SEM ~2.59
20
15
10
5
o
M
J
J
A
1989
SON
•
0
I
Iril
.:.J.....:.F-'M"--,==A~M'-J=-.:.J---'-'A
1990
Fig. 1. Density of oriental fruit fly in half.. and fully-ripe 'Sunrise' papaya fruits
sampled from fields with and without sanitation, May 1989-August
1990, Kauai, Hawaii. Each value shown is the mean number of larvae
per frult per month.
any infestation in mature green and color break fruits. He attributed the
infestation-free status of mature green and color break 'Sunrise' fruits to: (1) the
preference of ol"iental fruit fly females to oviposit in half-ripe and I'iper fruits; and
(2) the low population density of oriental fruit Oy adults in the orchard, which
consequently results in an extremely low probability of oviposition in the less
prefen'ed mature green and color break fruits. The practice of field sanitation in
'Sunrise' papaya orchard may, therefore, maintain the absence of oriental fruit fly
infestation in mature green and color break fruits.
Although, sanitation has long been recommended as a cultural method to
control Mediterranean fruit Oy, Ceratitis capitala (\Viedemann) (Back and
Pemberton 1918), oriental fruit fly <Van Zwaluwenbw'g 1947), and melon fly (Back
and Pemberton 1917, Nishida and Bess 1950, 1957) in several host commodities,
its practice has not been widely implemented in Hawaii because it is labor­
intensive, can be costly, and requires coordination and cooperation among
LIQUIDO: Suppression of Oriental Fruit Fly in Papaya
o
With sanitation
•
167
Without sanitation
25
Half ripe
20
OX =
0.47, SEM=0.27
• X=
2.85, SEM=I.32
OX =
• X=
23.49, SEM=4.35
15
;
~
.~
.
.E
c
10
·C
5
~
0
.c
~
~
."
~
~
~
.~
.E
0
70
Fully ripe
60
50
4.04, SEM=I.47
C
•~
40
~
a.
c
~
•
::;
30
20
10
o
M
J
J
A
SON
1989
D
J
F
M
A
M
J
J
A
1990
Fig. 2. Percentage infestation of oriental fruit fly in half- and fully-ripe 'Sunrise'
papaya fruits sampled from fields with and without sanitation, May 1989­
August 1990, Kauai, Hawaii. Each value shown is the mean percent
infested fruit per month.
neighboring growers. Sanitation may involve collecting ripe fruits on the ground
and unwanted fiuits on trees, shrubs, or vines and disposing these fruits either by
burrowing deep in the soil, burning, or application v.rith insecticides. Because of
the extreme polyphagy of oriental fruit fly (U. S. D. A. 1983), a sanitation program
may include removal of other breeding or alternate hosts growing within and
along borders of the field or orchard.
Data presented here clearly show that sanitation results in a significant
reduction of oriental fruit fly larval infestation in fruits and suppression of adults
in the orchard. The observed suppression of oriental fruit ny population in the
orchard by removal of ripe fruits on trees and on the ground may be explained by
two factors. One, sanitation limits the biomass of ripe fruits that are preferred by
females for oviposition and serve as suitable hosts ror larval development. Two,
removal of ripe fruits results in a significant reduction in number of oriental fruit
ny adults immigrating, foraging, and residing in the orchard. It must be
emphasized that sanitation maintained a low level oflarval infestation and adult
J. Agrie. EntomoL Vol. 10, No.3 0993}
168
Table I. Summary of repeated measure ANOVA on tbe infestation rates
(larval density per fruit, percent infested fruit, and relative
density of trapped adults) of oriental fruit fly in 'Sunrise'
papaya orchards with and without sanitation (May 1989August 1990, Kauai, Hawaii)ll. b, C
ANOVA values
df
SS
MS
1
8
8
0.419
0.853
0.467
0.419
0.107
0.058
7.72
1.96
1.07
0.009
0.086
0.407
1
8
8
0.032
0.052
0.049
0.032
0.006
0.006
12.46
2.49
2.34
0.001
0.033
0.043
1
13
13
8.446
8.458
2.533
8.446
0.195
76.88
5.92
1.77
0.0001
0.0001
0.076
Mean percent infested fruit
Field type
Time
Field type * time
1
13
13
1.319
1.055
0.612
1.319
0.081
0.047
73.23
4.50
2.61
0.0001
0.0001
0.008
Mean number adults per trap
Field type
Time
Field type * time
1
11
11
2.096
12.331
2.096
1.121
0.224
28.59
15.28
3.06
0.0001
0.0001
0.004
Source of variation
F
P
Half ripe
Mean larval density per fruit
Field type
Time
Field type
* time
Mean percent infested fruit
Field type
Time
Field type * time
Fully ripe
Mean larval density per fruit
Field type
Time
Field type * time
2.465
O.65L
Repeated measure ANOVA was performed on transformed data: Jog lo (mean larval density per fruit
+ 1), loglo (menn number adults per trap), and arcsine-Lransformed percenL infcsted froiL
h Field t.ype: with sanitation vs. without. sanitation.
r Time: includes only months during which the measured variables were> 0 for either one of the two
types of fields, or both.
Q
density in the clean, sanitary field despite its close proximity to abundant, suitable
reservoir hosts of oriental fruit fly. This observation strengthens the hypothesis
that field sanitation has a consequent significant reduction in adult immigration,
foraging, and residence in the orchard; i. e., reduction in number of females
foraging for food and oviposition site and males searching for mate and food.
Sanitation together with adult mass trapping and releases of sterile adults has
been successfully implemented in the suppression of several medically important
dipterous insects (Knipling 1979). Aside from the direct importance of field
sanitation in the integrated central oftephritid fruit fly pests, it has been proposed
LIQUIDO: Suppression of Oriental Fruit Fly in Papaya
169
Q With sanijation
• Wijhout sanijation
500,-----------------_
o X=
400
77.77, SEM=20.37
• X = 150.27, SEM=37.71
a.
~ 300
Q;
a.
-=>­
~
200
]g
c
.~
oc
100
'"
Q)
::;:
o
S
o
N
o
J
F
M
1989
A
M
J
J
A
1990
Fig. 3. Relative density of oriental fruit fly males caught in traps with methyl
eugenol + Naled per 4 h exposure in 'Sunrise' papaya orchards,
September 1989-August 1990, Kauai, Hawaii. Each value is the mean
number of adult males caught per trap per 4 h.
as a primary component of commodity quarantine treatments for papaya. For
instance, removal of all quarter-ripe and riper fruits on trees and the ground is
required for the certification of the proposed systems approach quarantine
treatment for tephritid fruit Oy infestations (which may include Mediterranean
fruit fly, Anastrepha spp., and Toxotrypa,na curvicaudata [GerstaeckerJ) in
'Sunrise,' 'I<apoho Solo,' and 'Waimanalo' papayas grown in Costa Rica and
intended for expOIt to the mainland United States (A. P. H. I. S. 1992).
Acknowledgment
I thank the technical assistance of Heide Ketter and Darlene Babin (USDA­
ARS, Kauai) for fruit collection and processing for fruit Oy infestation; and Paul
Barr and Lei Shinoda (USDA-ARS, Hilo) for data management. Special thanks are
extended to papaya farmers in Kilauea and Moloaa, Kauai for the cooperation.
170
J. Agric. Entomol. Vol. 10, No.3 (1993)
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