treatment, off- odors were noted in both broccoli and celery samples held in .... celery stalks ( Cel)after short- term exposures to air, 100% OOz, or 100% nitrogen.
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INTERNATIONAL SYMPOSIUM ON POSTHARVEST SCIENCE AND TECHNOLOGY OF HORTICULTURAL· CROPS Chinese Society for Horticultural Science American Society for Horticultural Science Asian Regional Center/AVRDC
June 27-July 1,1995 Beijing China
::=•
CHINA AGRICULTURAL SCI ENTECH PRESS
HIGH CARBON DIOXIDE TREATMENTS FOR INSECT DISINFESTATION OF CUT FLOWERS AND GREEN LEAFY VEGETABLES Marita Cantwell 1 , Xunli Nie 1 , Michael Reid2 , Alan Carpenter3 , and Ru- Jing Zong41 Depts. Vegetable Crops and
2
Environ. Hort., Univ .
California, Davis CA 95616 3
New Zealand Institute Crops and Food Research, Levin, N. Z.
4
Transfresh Corporation, 607 Brunken Ave., Salinas CA 93902
Abstract Long distance transport of horticultural commodities offers the opportunity to control common insect pests by prolonged exposure to low temperatures in combination with insecti'cidal atmospheres . Another alternative for postharvest inseci control is to apply more extreme short - term pre- transit controlled atmosphere treatments Various atmospheres enriched in carbon dioxide were evaluated for their efficacy in killi,ng adult aphids and thrips, common surface feeding insects on flowers and leafy vegetables. Short term (hours to days) treat ments with high
CO:z
levels ( 40 -;- 100% ) and long - term (at low temperature during usual
storage and transit periods) treatments with moderate C02 levels (10- 20%) were tested on lettuce, broccoli, roses and carnations at various temperatures ranging from Ot to 20t . Insect mortality was tested in similar atmospheres at Ot to 48t . Various treatment combinations are effective in achieving complete insect kill before the development of phytotoxic symptoms. Under moderate
COz concentrations,
adult insects (thrips) were killed in as little
as 7 days, although more typically kill was achieved after 10 to 14 days (aphids). Exposure of thrips and aphids to 60%
COz
in air showed that increasing the temperature from
20t increased adult insect kill (Table 1). At lower temperatures,
ot to
aphi~s were killed more
COz 100% COz
easily than thrips, whereas at 20t there were no differences in mortality. Under high concentrations, complete mortality was consistently achieved at Ot with 80 to
within 12 hours . The atmospheres need to be tested for efficacy on other life stages of the insects. A range of leafy vegetables and flowers were exposed to these high
COz atmospheres at
Ot to 20t and were found to tolerate the short exposures ( 8 - 24 hr) necessary for insect
kill. Introduction The U. S . Clean Air Act requires that any substance identified as ozone depleting be . 410 .
withdrawn from production, importation, and use in the U . S. by the year 2001. The principle uses of methyl bromide in agriculture are as a soil fumigant for pests and diseases and as a broad- spectrum postharvest fumigant ( Civerolo et al. , 1993) . Among the postharvest alternatives being investigated are other chemical fumigants, and biological and physical treatments. Recent work has demonstrated that carbon dioxide - enriched atmospheres ( > 20% ) were effective in killing surface feeding insect pests such as aphids, thrips, and omnivorous leafrollers on harvested horticultural commodities, as well as fruit pests such as codling moth (Carpenter and Potter, 1993; Fleurat - Lessard,. 1990; Ke and Kader, 1992) . Modification of the oxygen concentrations (in the range of 0. 25 - 12%) was much less important in affecting insect mortality than time of exposure and temperature: Carbon dioxide offers several advantages as a potential quarantine treatrment: postharvest quality of some products is benefited by carbon dioxide exposure, c~ is an effective fungistat at concentrations> 10%;
C~
is a readily available non- chemical control measure
which could be safely incorporated into current postharvest handling systems;
C~
is an envi-
ronmentally benign treatment which should be acceptable to all consumers. Two approaches can be taken. The first is to provide in - transit low
temperature~.
treatments, the effectiveness of which has already been demonstrated on a limited range of insects (Zheng et al., 1993). Recent technical advances in refrigerated container construction and monitoring systems now make it feasible to treat produce' with insecticidal CAs during the transport period . Another approach is to
pr~vide
short - term very high
C~
pre -
transit or in - transit treatments ( > 40% ) and these have been demonstrated to be particularly effective for hard to kill insect stages such as eggs and pupae (Carpenter and Potter,
1993). Tolerance to controlled atmospheres historically has been based on their use as longterm storage treatments. Other CA combinations need evaluation for their potential as methyl bromide alternatives. Both efficacy in disinfestation and tolerance by the products are essential criteria for acceptable quarantine treatments; this paper presents the results of some of these extreme atmosphere combinations.
Materials and methods Test products were obtained directly from growers or a local distributor and treated within 2 days of harvest unless otherwise noted . After selection, products were placed in glass containers in flow systems through which humidified air or controlled atmospheres were applied. Flow rates were initially high ( 10 x normal rate) and then were changed to normal rates (rates to keep C02 in air controls< 0 . 5%) . Atmospheres were monitored by periodic injection of gaseous samples on a sequential infrared - oxygen analyzer . Aphids (green peach) and injection thrips were collected on leaf samples from the field or greenhouse and placed in 20 to 30 - insect replicates in ;creened containers inside the product containers. After treatment, insects were held in air at 20'C for 3 - 4 hours . Insect mortality was
. 411 .
determined directly by gently brushing insects onto a sample grid and examining under a low -power microscope. Depending on the controlled atmospheres tested, products were generally stored for an additional period at typical storage temperatures in air and then evaluated after 3-6 hours at 20'C in air. Products were evaluated for visual quality, treatment-
in~
duced discoloratons or defects, and aroma. Commodity tolerance was based on the days for slight injury and/or slight off- odor to occur (a score of 2 on a 1 to 5 scale, where 1 =no off -odor, 5 =severe) and/ or visual quality to decrease below "good" (a score of 7 on a 9 to 1 scale, where 9 =excellent, 1 = unuseable). Cut flowers were placed in vases under controlled light at 20'C and their vase -life (loss of aesthetic appeal) determined. Three replicates were routinely used for all experimental conditions. Results and conclusions A range of quarantine insects are found on leafy vegetables and cut flowers. We have focused on the possible use of long- term (in transit) or short- term (pre- or post - transit) controlled atmosphere treatments for disinfestation of these commodities, using the common insects thrips and aphids as our models. Most of the work presented here focuses on shortterm treatments. Initial experiments indicated that relatively brief exposures (a few days to 1 week) to C~
- erujched atmospheres ( 10 - 30%) were effectiYe in killing adult thrips and aphids
with minimal phytotoxicity at low temperatures (Table 1) . Low oxygen in combination with 10%
~was
effective in achieving 100% mortalit;y of thrips by 7 days, but required>14
days for complete aphid kill at these low temperatures. All the products except lettuce could tolerate various treatment combinations which caused complete insect mortality. Further details of insecticidal atmospheres appropriate for storage and. long distance in - transit situations are described elsewhere ( Fleurat - Lessard, 1990; Potter et al. , 1994; Reid and Cantwell, 1994). Exposure of thrips and aphids to higher carbon dioxide concentrations showed that 60% ~in
air resulted in greater insect kill as the temperature increased form O'C to 20'C (Table
2), although high levels of mortality were achieved at storage temperature ( O'C). At the lower temperatures, aphids were killed more easily than thrips, whereas at 20'C there were no differences in mortality . We have extended these interesting fin'dings by examining the response of insects and commodities over a wider range of
C~
concentrations and temperatures. The response sur-
face for adult Western flower thrips (Frankliniella occidentalis) indicated that there was an increase in the insecticidal activity of C~ with increasing temperature (Tables 3 and 4). We found that relatively short exposures to very high c~ concentrations ( 80 - 100% c~) resulted in complete kill of adult thrips even at the low temperatures. Oxygen concentrations had more effect on mortality when combined with lower
C~
concentrations . From the re-
sults reported in Table 3 which was carried out with greenhouse insects collected in the summer, the thrips appeared to be weak as indicated by their high mortality even in air at low
. 412 .
temperatures . The susceptibility of other life stages of thrips were briefly studied under the same range of atmosphers used in Table 3 . As reported for other insect species, we found that second instar larvae were more tolerant than adults to the high C02 atmospheres tested, and pupae were more tolerant yet (data not shown). Longer exposures at intermediate and lower temperatures may result in adequate mortality of these more resistant stages. We have tested the tolerance of a range of commodities (fruits, flowers and vegetables) to these atmospheres and found them to be surprisingly tolerant of short exposures ( 4 - 24 hr) to these high concentrations of~ even at elevated temperatures. The results from the extreme conditions of applying 100% nitrogen are shown in Table 5 for four products. Lettuce did not tolerate high
c~
beyond 4 to 8 hours of treatment. After 24 hours of
treatment, off- odors were noted in both broccoli and celery samples held in the nitrogen atmospheres. Exposure of products to these atmospheres at temperatures above 20'C usually resulted in decreased visual quality. Notwithstanding the limitations noted, many products can tolerate short- term extreme insecticidal atmospheres . References
1. Carpenter, A. and M . A. Potter 1993. Controlled Atmospheres .• tn: ] . K. Sharp and G. J. Hallman (eds.). Quarantine Treatments. Westwood Press, Colorado. Chapter 12. 2.Civerolo, E.L., S.K. Narang, R . Ross, K . W. Vic~andL. Greezy(eds.). 1993 . Alternatives to methyl bromide: assessment of research needs and priorities. Proc. USDA Workshop Alternatives to Methyl Bromide, June 29 - July 1, 1993, Arlington, VA. 66 pp. 3. Fleurat- Lessard, F . 1990 . Effect of modified atmospheres on insects and mites infesting stored products . In: M . Calderon and R. Barkai- Golan, eds. Food Preservation by Modified Atmospheres. CRC Press, Boca Raton, Fl. pp. 21 - 39 . 4 . Ke, D. and A. A . Kader. 1992. Potential of controlled atmospheres for postharvest insect disinfestation of fruits and vegetables. Postharvest News and Information 3: 31N- 37N .
5. Potter, M. D. , A . Caq)enter, A, Stocker, and S . Wright. 1994 . Con trolled atmospheres for
the
postharvest
disinfestation of
adult
New
Zealand
flower
thrips
( Thysanoptera: Thripidae). ] . Econ . Entomology, in press. 6.Reid, M .S. and M. I. Cantwell. 1994 . Use of controlled atmospheres for control of thrips and aphids in harvested leafy greens and cut flowers. Dept Environmental Horticul- . ture, UC Davis, Final Report to CDFA, 13 pp. 7.Zheng, J . M ., M . S. Reid, D.Y . KeandM . I. Cantwell. 1993 . Atmospheremodification for postharvest control of adult aphids and thrips on flowers and green leafy vegetables. Proc . 6th Ind . Controlled Atmosphere Conference. NRAES - 71 . pp . 394 401.
. -113 .
Tab~
1
Insect and commodity tolerances to various controlled atmospheres at 0 or S"C •
J Temperatures and Atmospheres
Days for 100% Mortality'
'
Commodity Tolerance (days)b
Aphids
Thrips
Rose
>21
>21
>21
>21
>21
Broccoli
Lettuce
>21
>21
>21
>21
>21
>21
21
>21
>21
21
7-14
14-21
15-20
9
13
>2 1
21
21
21
17
14 -2 1
14-21
>21
>21
>21
14-21
14-21
>21
>21
>2 1
>21
7
7-14
7 -1 4
>21
4
11
O'C Air
>6
6
>1"4
>14
>14
>6
>~'!(,~
(It; Air ~
2%
0 .5 %
~ ~
0.02%
st:
Air ~
2%
0.5%
~
0 . 02%
~
Carnatio
>6
>6
>14
>14
>14
6
30%~
4
4
4
2
5
50%~
4
4
2
6 6.
2
5
Air
>6
>6
>6
>6
>6
>6
10%~
6
>6
>6
>6
>6
5
30%~
6
4
2
6
2
4
st:
50%~
6
4
1
6
2
3
> 14
> 14
> 14
>14
>14
> 14
10% C02
>1 4
7
> 14
>14
> 14
6
1%~+10%C02
>14
7
>14
>14
>14
6
>14
7
;
>14
>14
> 14
6
> 14
> 14
> 14
>1 4
>14
5
2%~+10%C02
> 14
14
> 14
> 14
>1 4
5
1%~+10%~
>14
7
> 14
>14
> 14
7
>14
>14
> 14 . >14
5 5
O'C Air ~+
2%
0 .5% 5'C
~+10% ~
Air
0 . 5% ~+ 10%
,.
COz
I
•
a Data were from non- feeding insects; more time was required for feeding thrips, but not aphids b Commodity tolerance based on days to slight injury and/or slight off- odor, or visual quality scored as fair.
The roses were red, carnations were pink and white, and iceberg lettuce was used .
Table 2
Mortality of feeding adult aphids (green peach) and thrips
(Fr.ankliniella occidentalis)
with short- term exposure to 60% C02 in air at O"C , lOt: and 20't . Data are from 3 experiments, and are calculated from 60 insects per treatment per experiment. % Mortality Aphids
Exposure
Thrips
O'C
10'C
20'C
O'C
10'C
20'C
24hr
86
95
89
46
30
89
36
97
99
100
67
47
100
48
97
100
100
75
78
100
60
99
100
100
88
93
100
Air, 60 hr
17
22
13
9
8
13
. 414 .
I
Table 3
Mortality of feeding adult thrips exposed to different controUed atmospheres for 4 or 8 hours at various temperatures. Data are means of four experiments, two for the 4 hour exposure and two for the 8 hour exposure; Data are means of 90- 120 insects per treatment. % Monality
Atmospberes/Temperature %~
%0z 21 0 0 0 0 .25 2 0 0 .25 2 0 0. 25 2
0 100 0 40 40 40 60 60 60 80 80 80
Table 4
Ot:
12'C
24'C
30t:
36t:
48t:
50 100 86 98 100 81 81 78 92 100 100 100
48 100 65
46 100 80 tOO
29 86 95
84
88 92 100 70 100 75 75 100
66 100 100 92 97 100 100 62 100 85 85 100
98 100 100 100 100 100 100 100 100 100 100 100
90 90
80 91 62 92 68 100 100
99
80 100 69 100 78 100 100
Mortality of feeding adult thrips exposed to air, and to 80°4 (In air) and 100% carbon dioxide atmospheres at Ot: or lOt • Data are means from 60 Insects per treatment per experi-
ment; data from 2 experiments are reported. %Monality 80%
Air Ot: 6 5,3 9,8
4hr 8hr 12hr
co;
lOt:
Ot:
10'C
5 5,6 7,6
8 35,31
· 12 14,31 100,100
100,90
100% C02 ot: 20 48,45
10'C 20 22,28
100,100
100,100
•- !-.,_~
Table 5
Overall visual quality of pink rnses (Ros), pink carnations (Car), broccoli heads (Bro) and celery stalks ( Cel)after short- term exposures to air, 100%
OOz,
or 100% nitrogen. Prod-
ucts were stored 1 week at Ot: before treatment and evaluated after an additional week at ot: in air plus 6 hrs at 20t:. A score of 9 =excellent and 1 = unuseable. Visual Quality Temp Time
100% C0 2
Air
100% nitrogen
Car 9 9 9 9
Cel
4hr 8 16 24
Ros 9 8 9 9
Bro
Ot:
9 9 9 9
9 9 9 9
Ros 7. 5 6.5 6.5 4. 5
Car 9 9 9 9
Bro 9 8 8.5 7
Cel 8.5 8 7 7
lOt:
4 8 16 24
9 8 9 8
9 8.5 9
9 8 .5
9
7.5
9 8 8 7. 5
8
9
9 8 9 9
8. 5 8 1. 5 8
·4 8 16 24
9 9 9
9
8.5 7.5
9 9 8
8 8 7
9
7
8.5 9 7
7
7
8
7
8
20'(;
8 --
8 7 7
9
9 9
8 7
Ros
Car
9 8.5 6.5 7
9 9 9 9
Bro 8.5 8 8.5 8.5
8 1.5 8 7
8 8
8 8 8 7
8 7.5 8
9 9 8.5 7
8 8 6 6
9 9
8.5 8 7. 5 7
8 8 6.5 7
9
8
7
9 8 7
8
5
9
Cel 9 9 9 8.5
------
. 415 .
