Greenhouse Investigations on the Effect of Guava on Infestations of Asian Citrus Psyllid in Grapefruit

REFEREED MANUSCRIPT
Proc. Fla. State Hort. Soc. 121:104–109. 2008.
Greenhouse Investigations on the Effect of Guava on
Infestations of Asian Citrus Psyllid in Grapefruit
D.G. HALL1*, T.R. GOTTWALD1, N.C. NGUYEN2, K. ICHINOSE3, Q.D. LE2,
G.A.C. BEATTIE4, AND E. STOVER1
1USDA-ARS, U.S. Horticultural Research Laboratory, Fort Pierce, FL
2Southern Fruit Research Institute, Ministry of Agriculture and Rural Development,
Mytho City, Vietnam
3Japanese International Research Center for Agricultural Sciences, Ishigaki, Okinawa-den, Japan
4University of Western Sydney, Centre for Plant and Food Science, University of Western Sydney,
New South Wales, Australia
ADDITIONAL INDEX WORDS. Diaphorina citri, huanglongbing, citrus greening disease
Reports from Vietnam indicate interplanting guava with citrus reduces infestations of Asian citrus psyllid (ACP)
(Diaphorina citri) in citrus. We therefore conducted cage studies in a greenhouse to assess the effect of different guava
cultivars on adult ACP mortality and settling behavior on citrus (young potted grapefruit). The effects of cotton and
tomato were also evaluated in some tests as non-citrus, neutral host species. Survival of adult ACP con?ned to potted
guava in no-choice situations was reduced as compared to survival on potted grapefruit. However, adult survival was
also reduced when they were con?ned to potted cotton or tomato. Adult ACP released into cages containing only citrus
generally moved faster to citrus than when either ‘White’ guava or cotton was present. Greater numbers of adults were
consistently observed on citrus over time in cages with only citrus as compared to in cages with citrus in the presence
of guava or cotton. This may have been due to differences in the total plant surface area in cages with citrus alone
compared to citrus caged with another plant. Mortality rates of adults were increased in cages containing both citrus
and guava in one of two studies. While signi?cant reductions in infestations of adults on young grapefruit sometimes
occurred in cages containing both citrus and guava in the greenhouse, the reductions were not enough to verify the
Vietnamese guava effect.
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama ACP and, consequently, incidences of citrus greening disease
(Hemiptera: Psyllidae), is an important pest of citrus in Florida, in citrus are greatly reduced when citrus is interplanted with
primarily because it is a vector of “Candidatus Liberibacter asi- guava, Psidium guajava L. (plant family Myrtaceae) (Beattie et
aticus” (Halbert and Manjunath 2004). This and other species of al., 2006). These observations were made in high density plant-
“Ca. Liberibacter” are phloem-limited, non-culturable bacteria ings of citrus that were intercropped with guava at a one-to-one
responsible for citrus greening disease (huanglongbing) (Halbert tree ratio [2.5-m (8.2 ft) row spacing, 2.5-m (8.2 ft) tree spacing
and Manjunath, 2004; Hung et al., 2004). Citrus greening is con- along rows]. It is speculated that guava volatiles or phytotoxins
sidered to be one of the world’s most serious diseases of citrus might be responsible for reducing infestations of the psyllid on
(Bové, 2006). Citrus trees infected by this devastating disease may citrus. Putative guava volatiles may interfere with the psyllid’s
only live 5 to 8 years, during which time they produce misshapen, ability to locate and infest citrus grown next to guava, or they
inedible fruit (Bové, 2006; Gottwald et al., 2007). ACP was ?rst might repel psyllids away from citrus. Putative guava toxins
found in Florida during June 1998 (Tsai and Lui, 2000) and is might negatively affect the biology of the psyllid, interfering
now established throughout the state’s citrus-growing regions with psyllid reproduction in citrus.
(Michaud, 2004). Citrus greening was found in Florida during late
The reports from Vietnam prompted greenhouse investigations
Aug. 2005 (Gottwald et al., 2007) and was subsequently shown in Florida. Three experiments were conducted to assess survival
to be widespread, especially in southern areas of the state.
of adult psyllids con?ned to citrus, guava (cultivars available in
Recent reports from Vietnam indicate that infestations of Florida), and other plants in no-choice situations. Two experi-
ments were conducted to assess settling behavior and survival of
adult psyllids in cages containing a young citrus plant by itself,
A
in cages containing both young citrus and guava plants, and in
CKNOWLEDGMENTS. The authors acknowledge and thank Matt Hentz and Kathy
Moulton, USDA-ARS Fort Pierce, for their contributions to this study. This article cages containing both young citrus and cotton plants.
reports the results of research only. Mention of a trademark or proprietary product
is solely for the purpose of providing speci?c information and does not constitute
Materials and Methods
a guarantee or warranty of the product by the U.S. Department of Agriculture
and does not imply its approval to the exclusion of other products that may also
be suitable. This research was supported in-part by a Florida Department of
The insects for the studies were obtained from a colony estab-
Agriculture and Consumer Service Grant.
lished during early 2000 at the USDA-ARS U.S. Horticultural
*Corresponding author; email: david.hall@ars.usda.gov; phone: 772-462-5897
Research Laboratory, Fort Pierce, FL. Originally collected from
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Proc. Fla. State Hort. Soc. 121: 2008.

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citrus, the psyl ids have since been continuously reared in Plexiglas experiment 1 and start of experiment 2. The adult psyllids were 1
(0.6 × 0.6 × 0.6 m) (2 × 2 × 2 ft) or BugDorm-2 cages (60 × 60 to 2 weeks old at the beginning of the test. The test was initiated
× 60 cm) (24 × 24 × 24 inches) (MegaView Science Education 1 May 2007 and terminated 14 May 2007.
Services Co., Ltd., Taichung, Taiwan) containing potted orange
EXPERIMENT 3. Procedures of this experiment were the same
jasmine, Murraya paniculata (L.) Jack (plant family Rutaceae). as those of the ?rst adult survival experiment with respect to
The colony is maintained by adding new M. paniculata plants on a how psyllids were caged on plants and how many psyllids were
bi-weekly schedule using procedures similar to those described by introduced onto each plant, and the same test plants were used.
Skelley and Hoy (2004) with no introduction of wild psyllids.
An exception was that young tomato (Solanum lycopersicum L.)
(Florida dwarf ‘Lanai’) (plant family Solanaceae) plants growing
Adult survival in no-choice host plant experiments
E
in 0.5-L (1 pt) pots were substituted for the young ‘Pink Oval’
XPERIMENT 1. Adults were caged in a no-choice situation on plants. With respect to the plants that were used in the second
each of the following types of guava (each cultivar represented experiment, these were maintained in the greenhouse during
by two plants) in a greenhouse on 5 Mar. 2007: ‘White’ seedless the eight wk interval between the end of experiment 2 and start
guava, ‘Thai’ white guava, ‘Ruby Supreme’ guava, ‘Barbie Pink’ of experiment 3. The adult psyllids were about 25 d old at the
guava, ‘Pink Oval’ guava, and ‘Duncan’ white grapefruit (Citrus beginning of the test. The test was initiated 9 July 2007 and
paradisi Macf., plant family Rutaceae). All of the guava plants terminated 20 July 2007.
were 80 cm (31 inches) or taller except “Pink Oval’ guava, of
which both plants were seedlings 8 to 13 cm (3 to 5 inches) tall. Adult settling behavior and survival in choice situations
The taller guava plants were growing in 11.4-L (3 gal) pots and
EXPERIMENT 1. Forty adult psyllids (20 of each sex) were re-
the small ‘Pink Oval’ guava plants were growing in 0.5-L (1 pt) leased into BugDorm-2 cages (described earlier) containing either
pots. None of the guava plants had any ?owers or fruit except the a young citrus tree (‘Duncan’ grapefruit) by itself (treatment 1) or
‘White’ seedless guava plants, each of which had a few developing a young citrus tree with a young ‘White’ guava tree (treatment 2)
blooms. The grapefruit plants were seedlings 14 cm (6 inches) tall (10 replications). The young citrus trees were growing in 3.0-L
growing in 0.5-L (1 pt) pots. For the guava plants that were 80 (0.8 gal) pots and the guava were in 6.0-L (1.6 gal) pots. Each
cm (31 inches) or taller, one branch from each was selected and of the 10 cages containing a citrus plant was paired with one of
a 3.8L (1 gal) clear plastic container (7F18 Screw-Lid Canister, 10 cages containing both citrus and guava, and each pair was
Rubbermaid, Fairlawn, OH) measuring 14.5 cm (5.7 inches) in randomly placed together in a greenhouse [cages 1 to 2 m (3–7
diameter and 24 cm (9.4 inches) tall was placed over the end of ft) apart]. Psyllids were released into the cages on 29 Mar. 2007
the branch to house adult psyllids. We cut a narrow slit in the when they were approximately 16 d old. The number of adult
container’s lid [11 cm (4.3 inches) in diameter, the slit extend- ACP on each citrus tree in each cage was counted at 1.5, 3, 5, 7,
ing about 6.4 cm (2.5 inches) from the edge of lid through the 8 and 24 h after they were released into the cages and thereafter
center of the lid], which enabled us to slip the stem of a branch daily each morning (except on weekends) for 17 days. Data were
into the slit of the lid and to screw the lid into place. To counter collected daily (except weekends) on the number of dead adults
the weight of the containers, a string harness suspended from in each cage. Numbers of eggs and nymphs on each citrus plant
above was tied around each container. The containers had been were counted on days 7, 14, and 18 of the study by excising all
ventilated prior to the study by cutting a 10 × 10 cm (4 × 4 inch) ?ush shoots from each citrus tree leaving no immatures in the
opening on one side of the container and gluing a screen over the cage. The total numbers of dead and live adults in each cage
opening to prevent psyl ids from escaping. Each caged branch was were counted on the last day of the experiment, 13 Apr. 2007.
approximately 20 cm (8 inches) in length and generally consisted Data on numbers of adult psyllids settled on citrus and numbers
of 3 or 4 mature tough leaves, 3 or 4 fully expanded new leaves, found dead each day were plotted over time to visually compare
and 2 or 3 young developing leaves. Five male and ?ve female settling behavior and survival of adults in cages with citrus alone
adults (age not recorded) were placed into the container, and the to those in cages with both citrus and guava, and the data were
slit was sealed shut using a piece of foam rubber stuffed into the compared using paired t-tests (? = 0.05) (PROC TTEST, SAS
slit and around the stem of the branch. The small grapefruit and Institute, 2002). Mortality of adults over time in cages with citrus
‘Pink Oval’ guava plants were housed as whole potted plants in alone and citrus with guava was assessed using simple linear
the 3.8-L (1 gal) plastic containers (7F18 Screw-Lid Canisters regression (PROC GLM, SAS Institute 2002).
?tted with screened lids for ventilation). Five male and ?ve female
EXPERIMENT 2. This experiment was the same as the ?rst ex-
adults (age not recorded) were placed into the container and the periment with respect to assessing psyllid settling behavior and
lid was attached. Prior to the study, Plaster of Paris was used to survival in BugDorm-2 cages containing citrus alone (treatment
cover the soil of the small potted plants to expedite ?nding dead 1) and in cages with both citrus with guava (treatment 2). The
adults. For all infested plants, dead adults were tabulated each same size plants were used, and the same number of male and
day except on weekends until the end of the experiment on 16 female psyllids was introduced into each cage. However, in ad-
Mar. 2007.
dition to cages with citrus alone and cages with both citrus and
EXPERIMENT 2. Procedures of this experiment were the same guava, cages with citrus and cot on (treatment 3) were included for
as those of the ?rst adult survival experiment with respect to how comparison purposes. The cotton was growing in 3.0-L (0.8 gal)
psyllids were caged on plants and how many psyllids were intro- pots. Another difference in experiment 2 was that data on the sex
duced onto each plant. The exact same test plants were used except of psyllids found dead each day during the study were recorded.
young cot on (Gossypium hirsutum L.) (‘Tamcot 22’) (plant family The test was arranged in a randomized block design (blocked
Malvaceae) plants growing in 0.5-L (1 pt) pots were substituted on location in the greenhouse) with 10 replications. Adult psyl-
for the young ‘Pink Oval’ plants. With respect to the plants that lids introduced into the cages were approximately 10 d old. The
had been used in the ?rst experiment, these were maintained in study was initiated on 15 Aug. 2007 and terminated 4 Sept. 2007.
the greenhouse during the 6-week interval between the end of Numbers of eggs and nymphs on each citrus plant were counted
Proc. Fla. State Hort. Soc. 121: 2008.
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on days 7, 10, and 20 of the study following the same procedures with respect to numbers of adult ACP settled on citrus plants
as in the ?rst experiment. For each observation date, numbers during the ?rst 3 h after adults were released into the cages (Fig.
of adults settled on citrus and numbers of eggs and nymphs on 2a). Signi?cantly fewer adults were observed on citrus in cages
citrus in cages with citrus alone (treatment 1) were compared to containing both citrus and guava after 5, 7, and 8 h during the
numbers on citrus in cages with citrus and guava (treatment 2), ?rst day of the experiment and on 12 of the following 13 daily
and to numbers in cages with citrus and cotton (treatment 3), using observation dates. Mean numbers of eggs laid per ?ush shoot
analysis of variance for the randomized complete block design were signi?cantly lower on citrus in cages containing both cit-
(PROC ANOVA, SAS Institute, 2002), and mean comparisons rus and guava on one of three sample dates (Table 1). However,
were made using the Ryan-Einot-Gabriel-Welsch test. Mortality conclusions from this experiment regarding the effect of guava
of adults over time in cages with citrus alone, citrus with guava, on numbers of eggs laid on citrus were confounded by a limited
and citrus with cot on was assessed using linear regression (PROC
GLM, SAS Institute, 2002).
Results and Discussion
Adult survival in no-choice host plant experiments
Greater than 50% mortality of adult psyllids occurred in the
?rst experiment within less than 5 d when they were caged on each
of the ?ve different types of guava (Fig. 1A). All adults caged on
‘White’ or ‘Ruby Supreme’ guava were dead by 7 d. Greater than
90% of adults caged on ‘Duncan’ grapefruit survived during the
11 d study. In the second experiment, all adults caged on ‘Duncan’
grapefruit survived over the 13-d study (Fig. 1B). Similar to the
?rst experiment, greater than 50% mortality of adult psyllids oc-
curred within less than 5 d when they were caged on each of the
four different types of guava. However, survival rates on cotton
were similar to survival rates on guava. In the third experiment,
all adults caged on ‘Duncan’ grapefruit survived over the 11 d
study (Fig. 1C). Greater than 50% mortality of adult psyllids
occurred within less than 3 d when they were caged on each of
the four guava cultivars. Survival rates on tomato were similar
to survival rates on guava
These results indicated that adults of the Asian citrus psyllid
do not survive for very long when con?ned to guava, cotton,
or tomato in a no-choice situation, with relatively high rates of
mortality occurring within 2 d and greater than 95% mortality
occurring within 6 to 9 d. Psyllids observed on guava, cotton or
tomato during the studies were often in what appeared to be a
feeding position but, based on the poor survival of adults, the
psyllids were either unable to obtain from these plants nutrients
required for survival, or chemicals associated with the plants were
toxic. There was little evidence from these no-choice feeding
experiments in the greenhouse that any of the guava cultivars
might be much different than cotton or tomato with respect to
their effect on survival of adult psyllids in a grove.
Adult settling behavior and survival in choice situations
During the ?rst 8 h after releasing adults into the cages in experi-
ment 1, the adults in one cage containing only citrus (replication 7)
congregated in the northeast end of the cage and remained there.
By the next morning, 39 of the 40 adults were found dead on
the ?oor of this cage in the northeast corner. A similar incidence
occurred but at a lower death rate in two other cages containing
only citrus, with 15 and 16 dead adults found on the northeast
?oor of each cage. The attraction of psyllids to the northeast end
of the cages was attributed to their strong attraction to sunlight
and the particular locations of the three cages in the greenhouse.
Replication seven was dropped from the analyses. Mean ± SEM
air temperature in the greenhouse during the experiment was 24.4
± 0.1 °C (75.9 ± 0.2 °F).
Fig. 1. Survival of adult Diaphorina citri caged in no-choice situations. (A) citrus
There was no signi?cant difference in the ?rst experiment
(‘Duncan’ grapefruit) compared to ?ve guava cultivars (‘Barbie’, ‘Pink’, ‘Ruby’,
between the two treatments (citrus alone or citrus plus guava)
‘Thai’, and ‘White’); (B) same as A except cotton substituted for ‘Pink’ guava;
(C) same as A except tomato substituted for ‘Pink’ guava.
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Fig. 2. Settling behavior and survival of Diaphorina citri in cages with citrus
alone or with both citrus and ‘White’ guava (starting population of 40 psyllids
per cage): (A) mean number and SEM of adults settled on citrus; (B) cumulative
mean number and SEM of dead adults.
amount of ?ush suitable for oviposition for multiple females in
each cage. Signi?cant linear relationships were found between
cumulative mean number of dead adults per cage (Y) and day
of the study (X) for both citrus alone and citrus plus guava (Fig.
2b). For adults in cages with citrus alone: Y = 3.4 + 1.1X, slope
SEM = 0.1, F = 149.9, df = 125, Pr > F = <0.0001, r2 = 0.55. For
adults in cages with both citrus and guava, Y = 2.4 + 1.8X, slope
SEM = 0.1, F = 265.8, df = 125, Pr > F = <0.0001, r2 = 0.68. The Fig. 3. Settling behavior and survival of Diaphorina citri in cages with citrus
slopes from these regressions were signi?cantly different, indicat-
alone, citrus with cotton, and citrus with ‘White’ guava (starting population of
ing that mortality rates were faster among adults in cages with
40 psyllids per cage): (A) mean number and SEM of adults settled on citrus;
cumulative mean number and SEM of dead (B) males and (C) females.
both citrus and guava. A t-test indicated that the mean number
of dead psyllids found each day differed signi?cantly between
cages with citrus (mean ± SEM of 1.5 ± 0.1) versus cages with second experiment was 27.8 ± .02 °C (82.0 ± 0.1 °F). Signi?cantly
both citrus and guava (mean ± SEM of 2.3 ± 0.2) (t = –2.85, df greater numbers of adults were observed on citrus caged alone
= 178, Pr > |t| = 0.0049).
than on citrus caged with either guava or cotton during the ?rst 2 d
Mean ± SEM air temperature in the greenhouse during the after psyllids were introduced into the cages (Fig. 3a). Signi?cant
Table 1. Mean (SEM) number of Diaphorina citri eggs and nymphs/shoot on citrus in a cage with and without
a guava plant (settling behavior and survival experiment 1). All infested ?ush shoots were removed on
each observation day. Mean ± SEM air temperature in the greenhouse during the experiment was 24.4 ±
0.1 °C (75.9 ± 0.2 °F).

Mean (SEM) no. of immature D. citri per ?ush shoot
Treatment
Day 7z
Day 14y
Day 18x
Overallw
Citrus alone
318.7 (88.8)a
95.0 (10.2)a
48.5 (14.4)a
142.8 (34.8)a
Citrus with guava
275.9 (104.5)a
49.0 (14.5)b
33.2 (12.5)a
115.9 (39.5)a
zt = 0.31, df = 13, Pr > |t| = 0.76.
yt = 2.60, df = 14, Pr > |t| = 0.02.
xt = 0.80, df = 16, Pr > |t| = 0.43.
wt = 0.51, df = 47, Pr > |t| = 0.61.
Proc. Fla. State Hort. Soc. 121: 2008.
107

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differences between numbers of adults settled on citrus caged
Greater numbers of adults were consistently observed set led on
alone and numbers of adults settled on citrus caged with cotton citrus over time in cages with just citrus. In the ?rst experiment,
were observed on four of the following 13 observation dates. For increased mortality of adults in cages with both citrus and guava
citrus caged with guava, signi?cant differences between numbers may have in-part been responsible for fewer adults being observed
of adults on citrus caged alone and numbers of adults on citrus on citrus in these cages. Furthermore, in both experiments, the
caged with guava were observed on nine of the 13 observation presence of non-citrus leaf area may have simply diluted ACP
dates. Mean numbers of eggs and nymphs per ?ush shoot were efforts to ?nd and feed on citrus. The different outcomes of the
signi?cantly lower on citrus in cages containing both citrus and two experiments with respect to mortality rates of adults may
guava than in cages with just citrus on two of three sample dates, have been related to differences in the age of psyllids introduced
though cumulative numbers were not signi?cantly different (Table into cages (16 d old in the ?rst experiment, 10 d old in the second
2). Cumulative mean numbers of dead adults observed during the experiment) or differences in air temperatures. Mortality rates in
study indicated that mortality rates of male (Fig. 3b) and female cages with citrus alone were similar in each experiment, but lower
(Fig. 3c) ACP were similar among cages with citrus alone, citrus mortality rates occurred in cages with citrus and guava during
with guava, and citrus with cotton. Regression analyses indicated the second experiment (hotter conditions) than during the ?rst
similar mortality rates of adults in cages with citrus alone, citrus experiment (cooler conditions). In contrast, adult ACP survival is
with guava, and citrus with cotton (Table 3). Means ± SEM of usually longer under cooler conditions (Liu and Tsai 2000).
3.1 ± 0.3, 2.8 ± 0.3 and 2.6 ± 0.2 dead psyllids were found each
Reports from Vietnam indicate interplanting guava with citrus
observation day in cages with citrus, citrus and cotton, and citrus reduces infestations of ACP and its spread of citrus greening dis-
and guava, respectively. There were no signi?cant differences ease in citrus. In our greenhouse studies when citrus and guava
among these means (F = 1.6, df = 319, Pr > F = 0.03; main effect were caged together, signi?cant reductions sometimes occurred
F = 0.7, df = 2, Pr > F = 0.49).
in numbers of adults settled on citrus. Numbers of eggs laid on
Adult Asian citrus psyllids introduced into cages generally citrus were sometimes reduced and adult survival was reduced
moved to citrus faster when citrus was alone than when citrus in one experiment. We considered these reductions notable but
was with guava. The increase in overall plant surface area in less than anticipated. It is also notable that the presence of cotton
cages with guava might have been involved since psyllids were with citrus did not produce markedly different psyllid responses
also slow to infest citrus in cages with cotton. Unfortunately, than the presence of guava with citrus. It is possible that guava
little is known regarding how ACP ?nds a host plant. There may in?uence on psyllid behavior may have been more pronounced
be volatiles associated with citrus that attract migrating psyllids if a citrus genotype other than grapefruit had been studied. The
from long distances, or there may be citrus volatiles that attract ‘White’ guava plants used in our settling behavior and survival
psyllids that are already in close proximity. In addition to possible studies were genetically similar but not identical to the ‘Bom’ and
plant volatiles that attract the psyllid, there may be visual cues ‘Xaly’ white guavas interplanted with citrus in Vietnam (Stover
that attract adults to plants from short or long distances. Such et al., 2008). It was therefore possible that, due to genetic differ-
visual cues might be missing in cage studies.
ences, our guava plants were de?cient in the traits responsible
Table 2. Mean number of immature (eggs and nymphs) Diaphorina citri on citrus in cages with citrus alone,
citrus and cotton, or citrus and ‘White’ guava (settling behavior and survival experiment 2). All infested
?ush shoots were removed on each observation day. Mean ± SEM air temperature in the greenhouse during
the second experiment was 27.8 ± .02 °C (82.0 ± 0.1 °F).

Mean (SEM) no. of immature D. citri per ?ush shootz
Treatment
Day 7
Day 10
Day 20
Overall
Citrus alone
252.5 (31.8)a
112.8 (11.2)a
24.9 (3.7)a
93.5 (10.8)a
Citrus with cotton
235.9 (28.3)a
119.8 (17.2)a
11.6 (1.7)b
85.1 (10.7)a
Citrus with guava
152.7 (19.3)b
91.4 (12.5)a
16.7 (3.6)b
71.5 (8.0)a
zFor each column, means followed by the same letter are not signi?cantly different (? = 0.05), Ryan-Einot-
Gabriel-Welsch test.
Table 3. Mortality rates of male and female Diaphorina citri in cages containing citrus, citrus and cotton, or
citrus and guava based on simple linear regression of cumulative mean number of dead adults (Y) on day
of the study (X) (settling behavior and survival experiment 2).z
Sex
Treatment
Regression
Slope SEM
r2
F
Male
Citrus alone
Y = 1.5 + 0.8X
0.04
0.76
342.1

Citrus with cotton
Y = 1.7 + 0.7X
0.04
0.73
287.6

Citrus with guava
Y = 1.8 + 0.6X
0.04
0.70
253.8
Female
Citrus alone
Y = 3.2 + 0.6X
0.04
0.71
263.2

Citrus with cotton
Y = 1.5 + 0.7X
0.05
0.68
230.3

Citrus with guava
Y = 3.7 + 0.6X
0.06
0.49
104.6
Over both
Citrus alone
Y = 4.9 + 1.4X
0.06
0.82
507.1

Citrus with cotton
Y = 3.1 + 1.4X
0.06
0.82
478.8

Citrus with guava
Y = 5.7 + 1.3X
0.09
0.65
202.4
zFor each regression, df = 109 and Pr > F = <0.0001.
108
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for the Vietnamese guava effect on psyllids. If guava produces Gottwald, T.R., J.V. da Graca, and R.B. Bassanezi. 2007. Citrus
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citrus huanglongbing in vector psyllids: Application to the study of
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Document Outline

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