Heated-Controlled Atmosphere Postharvest Treatments for
Macchiademus diplopterus (Hemiptera: Lygaeidae) and Phlyctinus
callosus (Coleoptera: Curculionidae)
Author(s) :S. A. Johnson and L. G. Neven
Source: Journal of Economic Entomology, 104(2):398-404. 2011.
Published By: Entomological Society of America
DOI:
URL: http://www.bioone.org/doi/full/10.1603/EC10316
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COMMODITY TREATMENT AND QUARANTINE ENTOMOLOGY
Heated-Controlled Atmosphere Postharvest Treatments for
Macchiademus diplopterus (Hemiptera: Lygaeidae) and
Phlyctinus callosus (Coleoptera: Curculionidae)
S. A. JOHNSON1
AND
L. G. NEVEN2
J. Econ. Entomol. 104(2): 398Ð404 (2011); DOI: 10.1603/EC10316
ABSTRACT Nonchemical, environmentally friendly quarantine treatments are preferred for use in
postharvest control of insect pests. Combined high temperature and controlled atmosphere quarantine
treatments for phytosanitary fruit pests Macchiademus diplopterus (Distant) (Hemiptera: Lygaeidae)
and Phlyctinus callosus (Schöenherr) (Coleoptera: Curculionidae) were investigated to determine the
potential of such treatments for quarantine security. Field-collected, aestivating M. diplopterus adults
and P. callosus adults were treated using a controlled atmosphere waterbath system. This system
simulates the controlled atmosphere temperature treatment system (CATTS) used to control a
number of phytosanitary pests in the United States and allows for a rapid assessment of pest response
to treatment. Insects were treated under regular air conditions and a controlled atmosphere of 1%
oxygen, 15% carbon dioxide in nitrogen, at two ramping heat rates, 12 and 24⬚C/h. Treatment of both
species was more effective under both heating rates when the controlled atmosphere condition was
applied. Under these conditions of controlled atmospheres, mortality of P. callosus was greater when
the faster heating rate was used, but the opposite was true for M. diplopterus. This could be due to
the physiological condition of aestivation contributing to metabolic arrest in response to the stresses
being applied during treatment. Results indicate that the potential for the development of CATTS
treatments for these phytosanitary pests, particularly P. callosus, is promising.
KEY WORDS postharvest, controlled atmosphere temperature treatment system, heat, Macchiademus diplopterus, Phlyctinus callosus
Macchiademus diplopterus (Distant) (Hemiptera:
Lygaeidae), commonly known as the “grain chinch
bug,” and Phlyctinus callosus (Schöenherr) (Coleoptera: Curculionidae), commonly known as the
“banded fruit weevil,” are two key phytosanitary pests
of South African export fruit. They are indigenous to
South Africa, affecting a variety of fruit types, but they
have a very limited global distribution and are thus of
quarantine concern to countries importing fruit from
South Africa (Slater and Wilcox 1973, Barnes et al.
1986, CABI 2007, Pryke and Samways 2007, Johnson
and Addison 2008). M. diplopterus feeds and reproduces on wild grasses and cultivated grain crops, such
as wheat, Triticum aestivum L. During summer, adult
M. diplopterus seek shelter sites for aestivation (Myburgh and Kriegler 1967). Orchards that are in proximity to wheat Þelds often become infested with aestivating adults. M. diplopterus does not damage fruit,
but it can be found sheltering in grape (Vitis spp.)
bunches and pome (Malus and Pyrus spp.), stone
(Prunus spp.), and citrus (Citrus spp.) fruit, sometimes
1 Corresponding author: Department of Conservation Ecology and
Entomology, University of Stellenbosch, Private Bag X1, Matieland,
7602 South Africa (e-mail: [email protected]).
2 USDAÐARS, Yakima Agricultural Research Laboratory, 5230 Konnowac Pass Rd., Wapato, WA 98951.
entering at the calyx end of apples and pears, and the
navels of oranges. It is at this time that M. diplopterus
infests fruit being harvested and packed for export. P.
callosus females lay eggs in hollow spaces in plant
tissue and leaf litter (Barnes and Pringle 1989). The
larvae are soil-dwelling and feed on plant roots. After
pupation in the soil, emerging adults move into the
aerial parts of fruit trees. Adult P. callosus cause damage to trees and fruit by feeding on leaves, bark of fruit
stalks and directly on fruit, particularly affecting
grapes and apples. Management strategies for preharvest control of P. callosus are implemented and continuously improved upon, but such strategies are lacking, and they require development for M. diplopterus.
Cultural practices for posthavest control reduce the
threat of infestation. These include strategies implemented during harvest and transport of fruit and handling in the packhouse. However, speciÞc postharvest
treatments for these key phytosanitary pests are
needed. Other than the option of methyl bromide
fumigation, there are no effective postharvest treatments to ensure quarantine security against these
pests on packed fruit. The global phase-out in the use
and production of methyl bromide, according to the
Montreal Protocol (Anonymous 2000), has resulted in
this treatment becoming more expensive, as well as
April 2011
JOHNSON AND NEVEN: POSTHARVEST TREATMENTS FOR M. diplopterus
increasing efforts to develop suitable alternative postharvest treatments (Fields and White 2002). Methyl
bromide fumigation for quarantine purposes however,
is exempt from the phase out plan until alternatives are
available.
Potential alternative postharvest treatments include
the use of extreme temperatures, controlled atmospheres, irradiation, and biofumigation (Mitcham
2005, Heather and Hallman 2008, Lacey et al. 2009,
Neven et al. 2009, Neven 2010). Combining treatments
can improve efÞcacy by reducing time to mortality,
and in turn, reduced treatment times can help to
maintain fruit quality. One such combination treatment already developed is the controlled atmosphere
temperature treatment system (CATTS), in which
heat and a controlled atmosphere is applied to fruit
(Neven and Mitcham 1996). The controlled atmosphere, which has reduced levels of oxygen and elevated levels of carbon dioxide, together with the thermal stress of the heated environment affects insect
respiration and ultimately results in death. CATTS
treatments already developed include ones to control
codling moth, Cydia pomonella (L.); and western
cherry fruit ßy, Rhagoletis indifferens Curran in sweet
cherries, and codling moth and oriental fruit moth,
Grapholita molesta (Busck) in apples, peaches, and
nectarines (Neven 2005; Neven and RehÞeld-Ray
2006a,b; Neven et al. 2006). These treatments are attainable in two ton commercial-scale chambers
(Neven and RehÞeld-Ray 2006b) and have been included in the USDA-APHIS (2008) manual. The development of CATTS quarantine treatments is time
consuming and expensive. In an effort to speed up the
development of CATTS treatments for other insect
species, simulated-CATTS treatments using a water
bath system have been developed previously (Neven
2008). Without the expense of a laboratory CATTS
unit, a simple system comprising a water bath, insect
container, gas source, and gas analyzer can be used
to evaluate the potential for CATTS treatments for
various phytosanitary pests. This controlled atmosphere water bath (CAWB) system has been used to
test combined heat and controlled atmosphere
treatments on the eggs and larvae of Thaumatotibia
leucotreta (Meyrick) (Lepidoptera: Tortricidae),
another phytosanitary pest from South Africa
(Johnson and Neven 2010). The CAWB system was
used to establish the most tolerant life stage of this
pest to such treatments, which was determined to be
the fourth instar. Further developments of CATTS
technology against T. leucotreta will focus on this life
stage in determining effective treatments that still
maintain fruit quality.
In the current study, the CAWB system was used to
test treatments on M. diplopterus and P. callosus with
the view to also developing CATTS treatments for
these pests in the future.
Materials and Methods
Insects. Field collections of M. diplopterus and P.
callosus were done as insects were required for treat-
399
ments, and insects were used to test treatments within
2 wk of collection. Aestivating M. diplopterus adults
were collected from shelter sites under the bark of
blue-gum, Eucalyptus globulus Labill., trees near
Malmesbury in the Western Cape, South Africa. Aestivating adults were used to test these postharvest
treatments because M. diplopterus are in this dormant
physiological state when they are found on fruit. Insects were kept in the laboratory in ventilated plastic
vials with pieces of bark and corrugated cardboard to
provide shelter (⬇24⬚C; ⬇70% RH, and a photoperiod
of 12:12 [L:D] h).
Single-faced corrugated cardboard bands tied
around the base of fruit trees were used to collect P.
callosus adults from apple orchards in Elgin in the
Western Cape, South Africa. P. callosus adults are
active at night and seek shelter during the day. The
corrugated cardboard bands provide convenient shelter sites and are generally used in monitoring for
weevils in orchards and vineyards. Weevils were kept
in the laboratory in ventilated Perspex cages (390 by
290 by 300 mm) and fed on fresh Coprosma repens A.
Rich. leaves daily, until used in treatments (⬇24⬚C;
⬇70% RH, and a photoperiod of 12:12 [L:D] h).
CAWB System. A controlled atmosphere water
bath system comprising a programmable water bath,
an O2/CO2 gas analyzer and insect container, as described in Johnson and Neven (2010), was used to test
insect response to combination treatments. Premixed
cylinders of gas containing 1% O2, 15% CO2 and balance N2 were used to supply the controlled atmosphere (CA) to the insect containers. Heat treatments
also were run with regular room air (RA) instead of
CA, in which case room air was pumped by the gas
analyzer into the insect container. The ßow rate of gas
through the system was 1 liter/min. Relative humidity
in the insect container was monitored using iButton
data loggers and Climastats software (FairBridge
Technologies, Gauteng, South Africa). Temperatures
inside the test tubes (16 by 100 mm), extending from
the insect container, were monitored using thermocouples and a KM22 digital thermometer (Kany-May,
Herfordshire, England).
Relative humidity in the insect container during RA
treatments averaged 79.0 ⫾ 1.5 and 72.0 ⫾ 2.0% during
CA treatments. Temperatures in the test tubes lagged
1Ð2⬚C behind the water temperature as the water bath
temperature ramped up at both heating rates.
Treatments. The start temperature of water for all
treatments was 23⬚C and was increased to 45⬚C by
either a slow rate of 12⬚C/h, or a faster rate of 24⬚C/h.
Both heating rates were applied with the CA and with
RA. Each treatment (combination of time and atmosphere type) was replicated four times and 20 insects
(one individual per test tube) were used per replicate.
As controls, an equal number of insects were placed
into test tubes and left on the bench for the duration
of each trial. Before starting treatments, the open
insect container with insects in test tubes was lowered
into the water bath and left for 15 min to allow the
insects to settle and for the temperature to stabilize at
23⬚C. When treatments were started the lid of the
400
JOURNAL OF ECONOMIC ENTOMOLOGY
Vol. 104, no. 2
Table 1. Mean percentage corrected mortality ⴞ SE of M. diplopterus and P. callosus adults after RA and CA treatments at the 12°C/h
heating rate
Time (min)
Temp (⬚C)
Min at temp ⬎42⬚C
0
30
60
90
120
150
180
23
29
35
41
45
45
45
0
0
0
0
25
55
85
M. diplopterus
P. callosus
RA
CA
RA
CA
0 ⫾ 0.0
0 ⫾ 0.0
0 ⫾ 0.0
3.8 ⴞ 2.4
6.3 ⴞ 1.3
17.5 ⴞ 1.4
26.3 ⴞ 3.2
0 ⫾ 0.0
0 ⫾ 0.0
2.5 ⫾ 1.44
38.8 ⴞ 7.5
91.3 ⴞ 3.2
95.0 ⴞ 2.0
100 ⴞ 0.0
0 ⫾ 0.0
0 ⫾ 0.0
0 ⴞ 0.0
3.8 ⴞ 2.4
97.5 ⫾ 2.5
0 ⫾ 0.0
0 ⫾ 0.0
18.8 ⴞ 5.5
27.7 ⴞ 4.3
100 ⫾ 0.0
CA conditions were 1% O2 and 15% CO2. Start temperature was 23⬚C and end temperature was 45⬚C. Times are total times from start of the
heat treatment. n ⫽ 80 insects for all treatments. For each species, cases in which mortality under CA differed signiÞcantly from mortality under
RA are indicated in bold.
container was clamped down, heat ramping initiated
and gas ßow started. Heat ramping at a linear rate of
12⬚C/h to a Þnal temperature of 45⬚C took 110 min and
55 min at a rate of 24⬚C/h. Once reached, the Þnal
temperature was maintained for the duration of treatment. The effect of each timeÐtemperature combination was assessed at 30-min incremental time points,
after the start of treatment. This was accomplished by
turning off gas ßow to the selected insect container
and removing insects from test tubes to assess mortality. Each treatment ran in a closed system for the
duration of each time period. The numbers of live and
dead M. diplopterus and P. callosus were determined
immediately after treatment and conÞrmed 24 h later,
because in some instances insects seemed dead immediately after treatment but revived when left for a
while.
Statistics. AbbottÕs formula was used for calculation
of corrected control mortality for both species because uniform numbers of test and control insects
were used (Abbott 1925). Mean percentage corrected
mortality and SE were determined across replicates
for each time point. Mean percentage corrected mortalities were arcsine 公x transformed for further analysis. Factorial analysis of variance was performed on
the transformed data of each test subject in each
treatment using STATISTICA version 8 (StatSoft Inc.
Tulsa, OK). SigniÞcantly different means were separated using TukeyÕs honest signiÞcance difference
test.
Results
Control mortality for M. diplopterus and P. callosus
individuals held on the bench during each treatment
did not reach ⬎2%.
Comparison of Mortalities Based on Atmospheric
Conditions. For M. diplopterus, percentage corrected
mortality was signiÞcantly different under RA and CA
conditions at both the slow and fast heating rates. In
the 12⬚C/h treatment, higher mortality was achieved
under CA compared with RA at four of the time points
tested after the start of each treatment (F5,36 ⫽ 42.30;
P ⬍ 0.05) (Table 1). Percentage corrected mortality
increased rapidly under CA, between elapsed treatment times of 90 and 120 min, from 38.8 to 91.3%. By
treatment time of 120 min, insects had been held at
temperatures ⬎42⬚C for at least 25 min, but a further
60 min at high temperature was required for mortality
to reach 100% (i.e., after 180-min elapsed treatment
time and 85 min at temperatures ⬎42⬚C). Under RA
conditions, this same temperature treatment regime
resulted in only 26.3% mortality. In the 24⬚C/h treatment, signiÞcantly higher mortality was achieved under CA compared with RA during the last two treatment times (F5,36 ⫽ 4.81; P ⬍ 0.05) (Table 2). Despite
the more rapid heating rate used in this treatment, at
180-min elapsed treatment time, after insects had been
held at temperatures ⬎42⬚C for 133 min, 71.3% mortality was reached under CA, whereas 37.5% mortality
was reached under RA conditions.
Table 2. Mean percentage corrected mortality ⴞ SE of M. diplopterus and P. callosus adults after RA and CA treatments at the 24°C/h
heating rate
Time (min)
Temp (⬚C)
Min at temp ⬎42⬚C
0
30
60
90
120
150
180
23
35
45
45
45
45
45
0
0
13
43
73
103
133
M. diplopterus
P. callosus
RA
CA
RA
CA
0 ⫾ 0.0
0 ⫾ 0.0
15 ⫾ 3.5
18.8 ⫾ 4.3
22.5 ⫾ 3.2
28.8 ⴞ 8.0
37.5 ⴞ 6.6
0 ⫾ 0.0
0 ⫾ 0.0
13.8 ⫾ 2.4
23.8 ⫾ 5.5
38.8 ⫾ 11.1
67.5 ⴞ 2.5
71.3 ⴞ 2.4
0 ⫾ 0.0
0 ⫾ 0.0
5.0 ⴞ 2.5
100 ⫾ 0.0
0 ⫾ 0.0
0 ⫾ 0.0
30.8 ⴞ 4.6
100 ⫾ 0.0
CA conditions were 1% O2 and 15% CO2. Start temperature was 23⬚C and end temperature was 45⬚C. Times are total times from start of the
heat treatment. n ⫽ 80 insects for all treatments. For each species, cases in which mortality under CA differed signiÞcantly from mortality under
RA are indicated in bold.
April 2011
JOHNSON AND NEVEN: POSTHARVEST TREATMENTS FOR M. diplopterus
401
Fig. 1. Mean percentage corrected mortality ⫾SE at 12 and 24⬚C/h heating rates for P. callosus under RA conditions (a),
P. callosus under CA conditions (b), M. diplopterus under RA conditions (c), and M. diplopterus under CA conditions (d).
For P. callosus, percentage corrected mortality also
differed signiÞcantly under RA and CA conditions at
both heating rates. When 12⬚C/h heat rate was applied, mortality under CA was signiÞcantly higher
after 60- and 90-min elapsed treatment times (F3, 24 ⫽
9.91; P ⬍ 0.05) (Table 1), and 100% mortality was
achieved after only 120-min treatment and 25 min at
temperatures ⬎42⬚C. At this time, 97.5% mortality was
achieved under RA conditions. When the heat rate
was doubled, mortality under CA only differed signiÞcantly from that under RA after 60 min of treatment (F3,24 ⫽ 20.46; P ⬍ 0.05) (Table 2). The effect of
the faster heat rate improved efÞcacy of both RA and
CA treatments, with 100% mortality reached after only
90 min under both atmospheric conditions, when insects had been held at temperatures ⬎42⬚C for 43 min.
In comparison, P. callosus was more responsive than
M. diplopterus to both RA and CA treatments, requiring between 25 and 43 min at temperatures ⬎42⬚C for
effective levels of control to be achieved in treatment
times of ⱕ120 min. M. diplopterus was the more thermotolerant of the two species, reaching ⬍40% mortality under RA conditions. M. diplopterus was also was
more resistant to the CA treatment, requiring 85 min
at temperatures between 42 and 45⬚C for effective kill
to be achieved at the slower heating rate in 180-min
treatment time. At the faster heating rate ⬎133 min at
such high temperatures would be required for effective control.
Comparison of Mortalities Based on Different
Heating Rates. The expected effect of greater mortality at the faster ramping heat rate was seen for P.
callosus under both atmospheric conditions. Mortality
was signiÞcantly higher and reached 100% sooner, at
the faster heat rate for both RA (F3,24 ⫽ 99.71; P ⬍
0.05) (Fig. 1a) and CA conditions (F3,24 ⫽ 100.65; P ⬍
0.05) (Fig. 1b). P. callosus required 30 min less treatment time at the faster heat rate for effective mortality
levels to be achieved.
However, for M. diplopterus, the expected effect of
a faster ramping heat rate was only seen under RA
atmospheric conditions. Under CA, the doubled heat
rate produced lower mortalities than the slower ramping heat rate. Under RA conditions, mortality was
signiÞcantly greater at the faster heat rate than when
12⬚C/h was applied (F5.36 ⫽ 4.22; P ⬍ 0.05) (Fig. 1c).
While under CA, mortality was lower under the more
intensive heat treatment (F5,36 ⫽ 16.19; P ⬍ 0.05) (Fig.
1d). M. diplopterus required a substantially longer
treatment time at the faster heat rate for mortality,
comparable with that achieved by the slower heating
rate, to be reached.
Discussion
Extreme temperatures that are lethal to insects, or
severely limit activity, are referred to as their upper
and lower critical thermal limits (Chown and Nicolson
2004). One would expect a more intensive treatment
(e.g., increased rate of temperature change) to result
in poorer thermal tolerance and greater mortality,
essentially, a decreased upper thermal limit. However,
when under CA, the upper thermal tolerance of M.
diplopterus increased when rate of temperature
change increased. Although the current study does
not deÞne the upper critical thermal limits of M.
diplopterus and P. callosus speciÞcally, treatments performed here under RA give some idea of the responses
402
JOURNAL OF ECONOMIC ENTOMOLOGY
of these species to different heating rates. A study of
the methodology used in determining critical thermal
limits showed that rates of temperature change used
in protocols signiÞcantly affect critical thermal limits,
and thermal tolerance does not necessarily respond to
these changes as expected (Terblanche et al. 2007).
The expected response was seen here for M.
diplopterus and P. callosus when treated under RA, in
that greater mortality was seen when the heat rate was
doubled. Under CA, P. callosus still responded as expected. With the heat rate doubled, and the additional
stress of the CA environment, mortality was increased
even more. The surprising response of M. diplopterus,
with greater survival at the faster heat rate when under
CA conditions, requires further investigation. Consequently the interaction between the CA condition and
upper thermal tolerance also should be considered.
The general principle that a low oxygen environment
affects critical thermal limits causing a decline in upper thermal tolerance proposed by Pörtner (2001) was
tested by Klok et al. (2004). Authors found that the
principle does not necessarily hold true for insects,
where the tracheal gaseous exchange system provides
efÞcient enough oxygen delivery under conditions of
oxygen limitation.
The contrasting responses of M. diplopterus and P.
callosus under CA conditions in the current study
highlight some interesting aspects of the physiology of
these insects. The response seen in M. diplopterus may
be due to the reduced metabolic state during aestivation. In this reduced state, the constraints of a
heated controlled atmosphere may trigger another
form of metabolic arrest (Danks 1987), allowing for
greater survival of the treatment. SpeciÞc experiments
to determine the critical thermal maxima and minima
of the phytosanitary pests studied here are required to
advance the development of postharvest treatments.
The results seen here suggest the possibility that certain treatment protocols already developed for other
phytosanitary pests might be made more effective by
reducing the heating rate.
The response of another phytosanitary pest of South
African export fruit, Thaumatotibia leucotreta, to the
same CAWB treatments described here, has been investigated previously (Johnson and Neven 2010). In
that study the low O2, high CO2 environment of the
CA treatment improved efÞcacy above that of the RA
treatments at both heating rates. The different developmental stages of T. leucotreta eggs and larvae were
subjected to treatments to determine the most tolerant stages.
The most tolerant developmental stage of T. leucotreta eggs, the white egg stage, required a 150-min
exposure time to the 12⬚C/h CA treatment and 120
min at 24⬚C/h (Johnson and Neven 2010). The most
tolerant T. leucotreta larval stage, the fourth instar,
could not be controlled at 12⬚C/h, because effective
treatment time was considered to be much too long
and would probably have deleterious effects on fruit
quality before controlling larvae. At 24⬚C/h, effective
treatment time for the fourth instar was not speciÞcally determined but found to be slightly ⬎150 min
Vol. 104, no. 2
(Johnson and Neven 2010). Comparisons of the responses of T. leucotreta to CAWB treatments, and the
effective treatment times determined here for M.
diplopterus and P. callosus, allows for deductions to be
made as to which the most and least tolerant of the
three species would be. Based on the Þndings of both
studies it is clear that, of the three species and life
stages, T. leucotreta larvae were more tolerant than M.
diplopterus and P. callosus adults, at the slower heat
rate, requiring a CA treatment at 12⬚C/h for a substantially longer time than 150 min for effective control (Johnson and Neven 2010). However, at the faster
heat rate, M. diplopterus adults were the most tolerant
species, requiring slightly more than a 180-min CA
treatment. P. callosus adults were the least tolerant to
the heated CA treatments applied here at either heating rate. Also, because 100% mortality was achieved by
the 90-min time point for P. callosus under both RA
and CA at 24⬚C/h, a heat treatment alone also seems
to be very effective against P. callosus. Future CATTS
treatments developed for T. leucotreta and M. diplopterus
will easily control P. callosus on packed fruit. If single
treatments to control all three pest species are required,
the slower heat rate is not viable in terms of maintaining
fruit quality due to the time required to control T. leucotreta larvae. Thus, treatments at the 24⬚C/h ramping
heat rate would need to be focused on for further development of CATTS technology.
Of the commercial CATTS treatments already available for controlling codling moth and oriental fruit
moth on stone fruit, one is a 150-min CA treatment at
24⬚C/h ramping heat rate (USDAÐAPHIS 2008). In
comparison to CAWB treatment results for codling
moth and oriental fruit moth, T. leucotreta was found
to be more tolerant of heated CA treatments (Neven
2008, Johnson and Neven 2010). Codling moth and
oriental fruit moth are both present in South Africa
and also would be subject to phytosanitary restrictions
for certain markets. Ultimately, future CATTS treatments developed for T. leucotreta will allow for control
of codling moth and oriental fruit moth, if required.
Obenland et al. (2005) showed that the commercial
CATTS treatment mentioned above does not adversely affect the fruit quality and marketability of a
variety of stone fruit cultivars. Also, pilot studies on the
effects of heated CA treatments on plum cultivars
indicated that treatment at a ramping heat rate of
24⬚C/h helped to maintain storage quality (W. Witbooi, personal communication). Pome fruit storage
quality also reportedly beneÞted from CATTS treatments (Neven et al. 2001). M. diplopterus and P. callosus also affect table grapes as phytosanitary pests.
The effect of a heat treatment on the postharvest
quality of grapes is an important consideration for the
development of CATTS treatments for table grapes.
However, there is little published on the subject
(Pryke and Pringle 2008). Research conducted to investigate the use of vapor heat to control a pathogen
on table grapes also measured important quality indices after treatment (Lydakis and Aked 2003). Treatments at temperatures between 52 and 55⬚C for time
periods of ⬍30 min did not signiÞcantly affect the
April 2011
JOHNSON AND NEVEN: POSTHARVEST TREATMENTS FOR M. diplopterus
measured quality parameters. CATTS treatments lasting for just 30 min is not likely to control the insect
pests tested here; however, the CATTS treatments will
be performed at lower temperatures, so could possibly
still be successfully applied to table grapes.
Irrespective of the contrasting responses to changing heat rates, the efÞcacy of the combined heat and
controlled atmosphere treatments seen here holds
promise for the development of CATTS technology
for M. diplopterus and P. callosus. Further research is
underway to develop CATTS treatments for South
African phytosanitary pests by using a laboratory-scale
CATTS unit, with fruit quality assessments done in
conjunction with insect mortality determinations.
Acknowledgments
We thank Casper Nyamukondiwa for assistance with Þeld
collections and for performing the CAWB treatments. We
acknowledge the Centre for Statistical Consultation, University of Stelllenbosch, South Africa, for help with statistical
analyses. We also thank Drs. John Terblanche (University of
Stellenbosch) and Robert Hollingsworth (USDAÐARS, U.S.
PaciÞc Basin Agricultural Research Center, Hilo, HI) for
peer reviews of this manuscript. This research was funded by
the Deciduous Fruit ProducersÕ Trust.
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Received 25 August 2010; accepted 23 November 2010.