Insecticidal Controlled Atmosphere for Management of Sweetpotato Whitefly 1994 Proposal
whiiefly
I propose to continue my investigation on the use of controlled atmospheres
for management of whitefly. Results to date indicate that 8 hr of low O2
conditions created by venting with factory-mixed N2 gas (<2 PPM O2)
at 20′C kill most of the greenhouse and sweetpotato whitefly, regardless
of the developmental stage. The some treatment did not affect the subsequent
growth of unrooted or rooted cuttings of poinsettias. In comparison, for
certain cultivars, treatment at the flowering stage led to development
of phytotoxicity on bracts. A preliminary study on how temperature influences
the effects of controlled atmospheres demonstrated that a 4 hr exposure
of greenhouse whilefly eggs to the low-O2 conditions at 30′C resulted in
the same fatality rate as those treated for 8 hr at 20′C. The short-time,
high-temperature conditions may increase the potential for use of this
technique as a means of disinfestation of whitefly on a wide range of crops.
The objectives of this proposal are (1) to examine the length of time needed
at a range of temperatures to effectively control sweetpotato whitefly
and (2) to test how various species of plants tolerate the treatment.
2) INTRODUCTION AND LITERATURE REVIEW
Extensive crop loss caused by sweetpotato whitefly, since the outbreak
in California in 1991 , has stimulated considerable attention in the agricultural
community. Currently, increased application of available pesticides and
the practices of integrated pest management have failed to control this
whitefly, and the estimated economic losses in 1991 alone were over half
a billion dollars (Perring et al., 1993).
Use of controlled atmosphere (CA) for long-term storage and pathogenic
control on edible crops has been extensively investigated. The method refers
to changes in the composition of the air surrounding the commodity and
generally involves reduction of oxygen and/or elevation of carbon dioxide.
In recent years, the treatment has been reported to effectively control
Caribbean fruit fly (Benschoter, 1987), codling moth (Soderstrom and Brandl,
1987), and Son Jose Scale (Chu, 1992) on various commodities and has been
suggested as a possible quarantine treatment for imported edible crops
(Ke and Kader, 1992). Commodities differ in their susceptibility to CA
and the recommendations for the level of tolerance to reduced O2 and/or
elevated CO2 varies (Ke and Kader, 1991). The time required for 100% mortality
of an insect depends on the species, its developmental stage, and the temperature
and atmospheric composition during the treatment. There is, however, limited
information on the influence of temperature on the mortality rate of insects
during CA, perhaps owing to the rapid deterioration of edible crops stored
at high temperatures. Studies on Caribbean fruit fly (Benschoter, 1987)
and western flower thrips (Reid, personal communication), however, do indicate
that increasing the temperature may increase the insecticidal effect of
the treatment. In comparison to edible crops, the greater surface to volume
ratio of floricultural crops allow these commodities to tolerate high levels
of CO2 (Joyce and Reid, 1985) and the range of temperatures tolerated during
the growing stage is less limited than during postproduction handling of
edible crops.
With funding from AFE, we have been studying the effects of elevated
CO2 and reduced O2 on greenhouse and sweetpotato whitefly. We envision
that this technique could be used to prevent spread of whitefly that generally
occurs via shipment of infested plant material. By disinfesting plants
prior to planting in the field or in the greenhouse, the growing season
would begin with a low or with a negligible population of whitefly. Furthermore,
the method can be used in greenhouses that cannot be sprayed with insecticides
and in conjunction with IPM practices of biocontrol as there is no residual
on plants materials.
Our eady investigations demonstrated that the level and duration of
CO2 treatment required to kill egg and pupal stages of greenhouse whitefly
often resulted in the development of phytotoxicity on poinsettias. Further
studies revealed that low oxygen treatments (<2 ppm O2) had a greater
effect on all stages of whitefly with less damage to plants. We have thus
focused our effort on the use of low-O2 CA, created by venting with factory-mixed
nitrogen. The adult stage was most sensitive to the CA treatment with 100%
mortality occurring after an exposure time of < 2 hr at 20′C (Fig. 1a).
In contrast, eggs were most resistant to the treatment. After a 4 or 8
hr treatment with low-O2, 10% and 80%, respectively, of the eggs failed
to hatch (Fig. 1b). The nymphal stage of greenhouse whitefly was killed
by a 4 hr treatment while sufficient control of sweetpotato whitefly required
8 hrs (Fig. 1c). The pupal stage responded somewhat to a 4 hr treatment
but an 8 hr exposure was required to kill >80% of the pupae (Fig. 1d).
Populations of whitefly visible on poinsettia leaves a few weeks after
an 8 hr exposure to low-O2 at 20′C indicate the insecticidal effectiveness
of the CA treatment (Fig. 2): Leaves infested with eggs of sweetpotato
whitefly and treated with air were densely covered with pupae (Fig. 2a).
In comparison, little further development occurred on treated leaves (Fig.
2b).
Fig. 1 Effects of low-O2 treatment (< 2 ppm O2) applied at 20′C on
the percent (a) mortality of adults, (b) hatch of eggs, (c) mortality of
nymphs, and (d) emergence of pupae of (TOP) greenhouse whitefly and (BOTTOM)
sweetpotato whitefly. Data are means +/- SE.
An 8 hr low-O2 treatment tested lost year on nine cultivars of rooted
poinsettia cuttings from Paul Eche Range demonstrated that the treatment
did not affect subsequent growth (AFE proposal, 1993). The some treatment
tested on six cultivars this year led to the some conclusions. Additionally,
unrooted cuttings and flowering plants were treated to determine if the
low-O2 treatment would affect the rooting potential of the cuttings and
to explore the possibility of using this technique to quarantine saleable
plants.
Four weeks after the CA treatment, there were no differences in root
or vegetative growth detected between Fig. 2. Poinsettia leaves infected
with eggs of sweetpotato whitefly and exposed to (a) air or (b) 8-hr of
low-O2 at 20′C. Photograph taken a few weeks after the treatment when the
eggs on the control leaves had developed into pupae. unrooted cuttings
treated with air or with low O2 (data not shown). Considerable differences,
however, existed between cultivars when plants were treated at the flowering
stage (Table 1). Phytotoxicity symptoms, evident as areas of discoloration,
typically appeared 24 to 48 hours after the treatment. Of the six cultivars
tested, ‘Annette Hegg’ was most sensitive to the treatment followed by
‘Freedom’. Minimal phytotoxicity occurred on the other cultivars tested.
Experiments conducted to date thus indicate that low-O2 CA can be used
for disinfestation of both greenhouse and sweetpotato whitefly on unrooted
and rooted cuttings of poinsettias. However, selection of plants for their
tolerance to the low-O2 treatment would be necessary if the technique is
to be employed on fully-colored plants. Table 1 . Susceptibility of bracts
of six cultivars of poinsettias to the 8 hr, low-O2 treatment. The degree
of phytotoxicity was visually estimated, at 10% increments, as the percentage
of total bract area with discoloration. Data were collected 2 days after
the treatment and are means ± SE.
Cultivar
Phytotoxicity
Cultivar Phytotoxicity
(%)^z (%)^z
Celebrate II
0.1 c^y
Pink Peppermint
0.3c
Freedom
7.Ob
Supjibi
4.1c
Hegg. Red
31.4a
V-14 Glory
1.1c
z Percentage of area with symptoms of phytotoxicity.
y Means separated by Duncan’s multiple test, P=0.05.
The effect of temperature during the CA treatment was tested on
six cultivars of rooted poinsettia cuttings. The height and weight of nine
replicate plants measured 4 weeks after the treatment demonstrated that
there were no differences in growth between cuttings treated at 15, 20,
or 25′C (data not shown). In contrast, the insecticidal effects of CA on
Caribbean fruit fly (Benschoter, 1987) and western flower thrips (Reid,
personal communication) have been demonstrated to be dependent on the temperature
during treatment. In a preliminary experiment where eggs of greenhouse
whitefly were exposed to the low-O2 conditions at 30′C, we observed that
a 10′ increase in temperature significantly increased the lethal effects
of the CA treatment (Fig. 3). A four-hr treatment at 30′C killed as many
eggs as an 8-hr treatment at 20′C. Since eggs are the stage most resistant
to the CA treatment (Fig. 1), this result suggests that a 4- rather than
8-hr treatment, may be all that is needed to disinfest plant materials.
Additionally, the shorter treatment time would suggest that the technique
could be used on a wider range of crops.
3) OBJECTIVES AND ANTICIPATED BENEFITS
The main objective of this proposal is to determine the length of time
required to kill adults, eggs, nymphs and pupae of sweetpotato whitefly
at various temperatures. In addition, we will evaluate the tolerance levels
of various crops that are susceptible to whitefly infestation. The proposed
study will benefit the industry by providing growers with an environmentally-safe
method of controlling whiteflies. The relatively simple set-up will enable
all growers to establish their own mini-quarantine treatment. In this way,
growers can start their poinsettia as well as other crops with non-infested
plant material, and thus, reduce the hazards and expenses associated with
application of pesticides.
4) MATERIALS AND METHODS
A) Influence of temperature on effectiveness of insecticidal CA in
controlling various stages of whitefly Leaves of poinsettia infested with
egg, nymphal or pupal stages of whitefly will be collected from a colony
of sweetpotato whitefly and will be placed in covered containers with two
venting holes in order to allow continuous flow of air or factory-mixed
gas. Adult whitefly will be collected using an aspirator and will be treated
similarly. The CA chambers will be placed in temperature-controlled dark
incubators set at 15C, 20C, 25C, 30C, or 35C. The survival rate of the
various stages will be assessed at weekly intervals and will allow for
the passage of sufficient time for the development of insects into the
next developmental stage. Mortality of adults will be assessed at intervals
for up to 24 hr directly following the treatment.
B) Sensitivity of various crops to the low-O2 treatment The purpose
of this study is to test the susceptibility of various crops to the low-O2
treatment. Crops to be tested include coleus, geranium, gerbera, miniature
rose, Salvia farinacea, cantaloupe, and tomato, as they are economically
valuable and highly susceptible to whitefly. Plants will be propagated
in accordance with conventional means. They will be grown in the greenhouse
until the commercial stage, i.e. six-paks for some crops and 4″ pots for
others, and then treated with air or low-O2. The temperature and duration
of the treatments will depend on results obtained in Objective a. The susceptibility
of the plants to the low-O2 treatment will be evaluated by (1) assessing
the percentage of area with symptoms of phytotoxicity and (2) determining
the growth of the plants 2 to 4 weeks following the treatment. The degree
of phytotoxicity will be analyzed using Sigma Scan Image and will be expressed
as the percentage of the total leaf area with symptoms of phytotoxicity.
Plant growth will be determined by measuring height, fresh weight, and
dry weight.
C) Sensitivity of develoomental stages to the CA treatment The goal
of this study is to determine if the developmental stages of the plants
affect their response to the low- O2 treatments. Plants of crops, determined
by the results of Objective b, will be grown until they reach various developmental
stages. Plants will be treated and evaluated as described in Objective
b. 5)
LITERATURE CITED
Benschoter, C.A. 1987. Effects of modified atmospheres and refrigeration
temperatures on survival of eggs and larvae of the Caribbean fruit fly
in laboratory diet. J. Econ. Entomol. 80: 1223-1225.
Chu, C.L. 1992. Postharvest control of Son Jose scale on apples by controlled
atmosphere storage. Postharvest Biol. and Technol. 1: 361-369.
Joyce, D.C. and M.S. Reid. 1985. Effect of pathogen-suppressing modified
atmospheres on stored cut flowers. In: Blankenship (ed.). Controlled atmospheres
for storage and transport of perishable agricultural commodities. Hart.
Report. No. 126. NC State Univ., Raleigh.
Ke, D. and A.A. Kader. 1991. Potential of controlled atmospheres for
postharvest insect disinfestation of fruits and vegetables. Postharvest
News and Information. 3: 31-37.
Perring, T.M., A.D. Cooper, R.J. Rodriguez, C.A. Farrar, T.S. Bellows,
Jr. 1993. Identification of a whitefly species by genomic and behavioral
studies. Science 259: 74-77.
Soderstrom, E.L. and D.G. Brandl. 1987. Controlled atmospheres for postharvest
control of codling moth on fresh tree fruits. California Tree Fruit Agreement,
Sacramento. CTFA 1986 research report.
U.S. Department of Agriculture. Agriculture Research, Nov. 1992, p.
4-13.
6) BUDGET
The funds requested will support a half-time technician to work on the
project. A half-time technician is required for thorough investigation
since in the past each experiment was repeated at least 4 times and the
data collection is quite labor intensive. The request for supplies is to
support purchase of gas cylinders, pots, growing media, and other materials
which will be required to conduct this research.
Salaries (half-time technical support) $ 12,000 FICA (1.45%) $ 174
Supplies $ 1,500
Publication $ 500
Total $ 14,174
7) PROJECT LEADER QUALIFICATIONS
The principal investigator has a Ph.D. degree in plant physiology from
the Univ. of California-Davis and a M.S. in floriculture from the Univ.
of Missouri-Columbia. This educational background has enabled me to conduct
both basic and applied research that are critical to the floricultural
industry. My laboratory is well equipped with the atmospheric chambers,
growth incubators, glasshouses needed for the proposed study.
