. - - -- - --- . - - ---

. EFFICACY OF 'IDIPERATURE TREATNENTS FOR INSECTDISINFESTATION OF DRIED FRUITS AND ~11l'S

J. A. Johnson, H. R. Bolin, G. Fuller, A. A. Rhodes and J. F. Thompson

ABSTRACT

In order to determine the potential of various temperature treatments fordisinfesting dried fruits and nuts of postharvest insect pests, e>qx>suretimes for 50, 95 and 99% mortality in navel orangeworm eggs and pupae andIndiaruneal moth pupae were estimated. For navel orangeworm eggs, 99%mortality was achieved with a.-posure times of 194 minutes at 45°C and 14minutes at 49°C. Navel orangeworm pupae reacted differently totemperatures; 99% mortalities were produced at 37 minutes at 46°C and 12minutes at 49° C. Indiaruneal moth pupae were less heat tolerant, similarmortali ties were obtained at 42 minutes at only 420C and 13 minutes at46°C. Freezing points for various stages of the Indianmeal moth werealso determined. Pupae and diapausing larvae were the most freezetolerant, with freezing points of -25°C and -23°C, respectively. Thefreezing point for non-diapausing larvae was -15°C. The protocol forstudies on the effect of high temperatures on product quality wasestablished and experiments were begun. Infonnation on the engineeringand economic aspects of both high and low temperature treatments wasgathered and an analysis begun.

OBJECTIVES

The purpose of the study is the developnent of temperature treatments asalternatives to fumigation for insect disinfestation of postharvest driedfruits and nuts. In accomplishing this goal the following objectives havebeen set.

(a) Determine the temperature extremes and associated eA-posure timesrequired to kill various stages of the Indianmeal moth (INM), thenavel orangeworm (NO\v) and the driedfruit beetle (DFB).(b) Compare control efficacy of different heat application methodsagainst the above insects in infested raisins, prunes and walnuts.(c) Evaluate the effect of the above treatments on product quality.(d) Estimate and compare the costs and feasibility of the abovetreatments to currently used fumigants and other alternatives.

PROCEDURES

The mortality of pupae of the ThIN, and eggs and pupae of the NOWeA-posedto temperatures ranging from 42 to 49°C for different times wasdetermined. Treatments were applied in a water bath capable ofmaintaining constant temperatures with to. 20C accuracy. For IMMpupae,both direct hot water immersion and ind}rect immersion in small watertightcells were used to predict the efficacy of different heating methods. ForNOWeggs and pupae, only direct immersion was used. Data were analyzed toplot thermal death rate curves and predict LTsos, LT9ss and LT99Sfor each temperature.

107

Freezing points for I~~ pupae, non-diapausing larvae and diapausing larvaewere determined by cooling test insects at constant rates in dewar flasks

containing liquid nitrogen. Freezing events were observable as suddenincreases in insect surface temperatures as detected by thermocouples.

To deteI1uine the effect of high temperatures on product quality, various

protocols for each conunodity have been established. These protocols areoutlined in the flow charts in Fig. 6. In addition, researchers have

begun to gather the necessary infoI1f1ation for analysis of the economic

feasibility of temperature treatments for raisins, prunes and walnuts.Ini tial focus is on cOllunodity treatments most likely to be economically

feasible: in-transit heat treatments using modified "grain-driers",

in-storage heating, and cold-storage at above freezing temperatures (to

suppress insect activity and reproduction).

RESULTS

Percent mortalities from direct hot water iuunersion of L'M and NOW pupae

plotted against exposure time for each treatment temperature are given inFigs. 1 and 2. Exposure times that would provide 50, 95 and 99% mortality

(LTs 0, LT95, and LT99) were estimated using simple regressionanalysis, and are presented in Table 1. For both insects, a single degree

change in temperature resulted in considerable differences in LT values.

NOW pupae proved to be more heat resistant than II-JH pupae. The LTg 9 forNOW at 460C was nearly three times that for lit-I.To obtain NOW LTgg s

that were comparable to those of lil'lat 46°C, tile temperature had to beraised to 49°C.

In order to compare the effectiveness of the different heating u~thods

used for IMM pupae, the logs of the LTs 0s for each method were plotted

against temperature. LTs 0s of fenale INN pupae inuuersed in water-tightcells were very similar to those from direct iuunersiontests. Nale L'1l'1

pupae in cells appeared to be more heat tolerant, with higher LTsos forthe same temperatures (Fig. 3). Actually, because males were smaller thanfemales and were thus more irlsulated by air in the narrow cells, n~les

experienced a slower heating rate than females. The difference in heatingrate accounts for the apparent difference in mortalities, because a slower

heating rate increases the e'>"T.JOsuretimes necessary for the desired

mortali ty .

Percent mortalities for NOW eggs directly uwnersed in hot water were

plotted against exposure times for each temperature in Fig. 4. Again,simple regression analysis gave fairly accurate estulJations of LTsos,LT9SS and LT99S, and are presented in Table 2. At lower temperatures,NOW eggs were fairly heat toler< 194 Ininutes were required to produce

99% mortality at 45°C. At 49°C, the same mortality is obtained at 14

minutes. To compare the heat tolerance of NO\~ eggs with NO\v pupae, logs

of the LTsos for each stage were plotted against teJnperature (Fig. 5).Eggs proved much more heat tolerant than pupae at lower teJnperatures, but

this difference decreased as temperatures increased, with eggs less

tolerant than pupae at 49°C.

108

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]NM larvae and pupae were capable of surviving eA-posure to temperatureswell below 00C. IMN pupae proved most freeze resistant, the averagetemperature at which INH pupae froze ""as -24.9° C. Dio.pausing larvae,the natural overwintering stage of the insect, had. an average freezingpoint of -22.50C. Non-diapausing lar\'ae, with an average freezing pointof only -15.10C, were much less freeze tolerant than either dia.pausinglarvae or pupae.

The economic analysis of high temperature disinfestations was begun, andwill be based on the current cost of driers for products such IlS pistachionuts, walnuts, and dried prunes. Five separate types of driers that areused for these conunodi ties have ~n identified and data on their energyuse and capital costs have been collected. The complete financialanalysis of high temperature disinfestation will prob&.bly be based onusing these driers in their off season. These driers are idle for 10 to11 months per year and would be available for use. Also, they willprobably require very little modification in order to be used for .

disinfestation because they are already set up to harldle the crops that weare considering.

Low temperature disinfestation costs will be based on forced air coolingand storage operations which are commonly used in California's fresh fruitand vegetable industry. The off season for many of these facilities issix to nine months and we may assLUne that existing installations can beused for disinfestation in our financia.l analysis. We have collected. somecapi tal cost and energy use information for recently constructedfacilities.

Studies on product quality have been initiated; but results from storagetests are not available at this time.

OONCLUSI<1'lS

The results from the efficacy tests indicate that temperatures of as lowas 46°C for as little as 13 minutes would effectively control nr-I pupae.Both NOWeggs and pupae were more heat resistant; 49°C for 14 and 12minutes would be needed to control eggs and pupae, respectively. Whenboth insects are present, a treatment temperature of 50°C for 15 minutesshould insure complete control. Before final recommendations can be made,the thermal death points for larval and adult stages of both NOWand IMM,along with eggs of the IMMand all stages of the DFB, need to bedetermined.

The comparison of heating methods indicates that minor differences inheating rate can dramatically effect efficacy. This must be taken intoconsideration when treatment temperatures and eA'posures are predicted fordifferent heat treatments. Nore work needs to be done on the effect ofheating rate and transient temperatures on insect mortality.

The freezing point determinations indicate that the pupal stage of the nt-Iis the most freeze tolerant. This information will be useful whenlarge-scale low temperature disinfestation of cOJWllOdities are conducted.Freezing points for NOWand DFB must also be determined in order toidentify the most resistant species.

109

Preliminary engineering and econuJuic studies indicate that modifications

of existing dehydration procedures may provide the most economical heatdisinfestation of candidate cOJluuodities. The USe of existing lm-l

temperature facilities for disinfestation may also prove ucceptable.

110

Fig. 1 Thermal Death Points tor IMMPupaeDirect Immersion

Fig. 2 Thermal Death Pointstor NOWPupaeDirect Immersion

-111

100

% 80

SU 60rv

4°1 \:44C '\1va1 20

Ix

00 10 20 30 40 50

Time (Minutes)

100

% 80--

SU 60rv1 40VaI 20

00 10 20 30 40 60

Table I Lethal Times tor IMM and NOWPupae

.._ ._<_On' _

IMM NOW-- -- -----

LT50 LT 95 LT 99 LT50 LT 95 LT99

(minutes)

.-- --- --. .-.------

Fig. 3 Direct Immersion vs Dry Heatfor IMM Pupae

0.541

-1 I. L

42 43 44 45

Temperature,OC

46 47

112

42 27.7 40.6 41.8

43 19.128.429.2

44 13.2 19.7 20.3

45 9.5 16.5 17.2

46 7.4 12.4 12.9 24.0 35.6 36.6

47 - - - 16.9 23.4 23.9

48 - - - 10.8 17.117.7

49 - - - 7.2 11.3 11.6

-- - -

Fig. 4 Thermal Death Points for NOWEggs

%

surviva1

Fig. 5 Thermal J:fS01or NOWEggs vs Pupae

Log LTso2.5--- ---....---.-----.----.

*2

1.5.-

0.544

-~ _J L 1 1.--_

45 4~ 41 48o

T&mporolure.C

49 50

113

Table 2 Lethal Times tor NOW Eg"gs

L1' LT95 99

(minutes)

114

45 143.0 169.9 194.1

46 57.4 106.9 111.3

47 31.4 57.8 60.2

48 11.1 28.1 29.6

49 5.0 10.9 14.2

Fig. 6 Product Qual1ty Evaluations tor Temperature Treatmen ts

Procedures for Quality Evaluations for Prunes

Tasle )lanel

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