Biological Control 16, 81-87 (1999) ®Article ID bcon.1999.0737, available online at http://www.idealibrary.com on IDE~L

Life History Characteristics of Three Populations of Edovum puttleriGrissell (Hymenoptera: Eulophidae) at Three Temperatures

Nuris M. Acosta and Robert J. O'Neil

Department ofEntomology, Purdue University, West Lafayette, Indiana 47907-1158

Received November 10, 1998; accepted April 11, 1999

The exotic egg parasitoid Edovum puttleri Grissellhas shown promise for biological control of the Colo­rado potato beetle, Leptinotarsa decemlineata (Say).However, because the activity of currently availablepopulations is decreased at low temperatures, the useof biotypes of E. puttleri adapted to low temperaturesmay provide more effective control. To determine ifthere are populations of E. puttleri adapted to lowtemperatures, the life history characteristics of threepopulations collected in Honduras were compared atthree temperatures (15,24, and 30·C) over three genera­tions. In general, life history characteristics differedbetween the first generation and subsequent genera­tions. Among temperatures, parasitoids reared at 24·Cwere more reproductively active, lived longer, andsurvived better than those reared at other tempera­tures. At the lowest temperature, there was a signifi­cant difference in the frequency of total egg produc­tion, with females from the "River" collection siteproducing more eggs than females from the other twosites. Coincidentally, the River area is located at thehighest elevation and experiences a cooler climate.Comparison ofE. puttleri collected in Honduras, Colom­bia, and Mexico showed differences in life historycharacteristics. The implications for this study forselection ofbiotypes ofE. puttleri are discussed. © 1999

Academic Press

Key Words: Leptinotarsa decemlineata; Edovum put­tleri; egg parasitoid; biotypes; foreign exploration;Colorado potato beetle.

INTRODUCTION

The Colorado potato beetle, Leptinotarsa decemlin­eata (Say) (Coleoptera: Chrysomelidae), is the mostimportant defoliating pest of potato, Solanum tu­berosum L. (Hare, 1990). Because Colorado potatobeetle is an exotic pest in North America and Europe,foreign exploration for new natural enemies has beenconducted in its home range of Latin America (Puttlerand Long, 1983; Logan et a!., 1987). Edovum puttleriGrissell (Hymenoptera: Eulophidae), a solitary egg

parasitoid, collected in Colombia and Mexico, has beenevaluated for biological control programs in the UnitedStates (Ruberson et al., 1987). While showing promiseunder certain conditions, E. puttleri fails to overwinterin United States potato production areas (Obrycki etal., 1985). As a result, its use in augmentative biologicalcontrol programs has been suggested (Obrycki et al.,1985, 1987).

Populations of E. puttleri collected in Mexico andColombia have shown differences in their life historycharacteristics (Ruberson et al., 1987, 1988). For ex­ample, although the developmental response to tem­perature was similar for both populations, the Mexicanpopulation had higher survival at 15°C (Obrycki et al.,1987; Sears and Boiteau, 1989). Because the effective­ness of E. puttleri declines at lower temperatures,variation in its ability to tolerate low temperaturescould be overcome by artificial selection, by geneticengineering, or by identifying populations that areactive under low-temperature regimes (Obrycki et a!.,1985). However, there has been neither a directedsearch for such populations nor an extensive examina­tion of the life history characteristics of E. puttleri atlow temperatures (Obrycki et al., 1985).

E. puttleri has been found at relatively high eleva­tions (>1200 m) in Honduras (O'Neil, unpublisheddata). While a tropical country, Honduras has a distinctwet/dry seasonality and shows considerable variationin temperature as a function of altitude (Grolier Inter­active Inc., 1997). The potential isolation of popula­tions, their need to survive periods of adverse climaticconditions, and the existence ofE. puttleri at a range ofaltitudes suggest that there may be populations adaptedto local climatic regimes. The objective ofthis study wasto determine if E. puttleri populations collected inHonduras differ in their life history characteristics atdifferent temperatures.

MATERIALS AND METHODS

Populations of E. puttleri were collected in March1997 from parasitized eggs of L. undecemlineata Stal

81 1049-9644/99 $30.00Copyright © 1999 by Academic Press

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82 ACOSTA AND O'NEIL

on wild Solanum spp. from three sites in westernHonduras. The location and altitude of collection siteswere recorded using a Magellan GPS satellite locator(Magellan System Corp., San Dimas, CA.). The site"Marcala" (14°09'25/1 N; 88°00'58/1 W; 1279 m) is about25 kID. from the second site "La Paz" (14°15'30/1 N;87°47'57/1 W; 1360 m), and both are approximately 140kID. from the third site "River" (14°25'55/1 N; 89°07'59/1W; 1506m).

After collection in Honduras, parasitoids where main­tained as separate colonies on eggs of L. decemlineatain the Biological Control Laboratory at Purdue Univer­sity. Colorado potato beetles used as hosts for rearingand experiments were cultured following the methodsofValicente (1992). Potato plants (varieties Russet andKennebec) used to feed L. decemlineata were cultivatedfollowing the methods of Valicente (1992). Parasitoidcolonies were started with 9 parasitoids from River, 231from Marcala, and 264 from La Paz and were main­tained following the methods of Schroder et al. (1985).Briefly, adult parasitoids were maintained in cylindri­cal plastic containers (11 cm in diameter and 14 cm inheight) at 16:8 (L:D) photoperiod, 24 ± 2°C, and40-60% RH. A 1:4 honey-water solution deliveredthrough a dental wick was provided and changed asneeded. Every other day, eggs of Colorado potato beetle«48 h old) were provided for oviposition and hostfeeding. Following removal from the colony containers,eggs were kept in a cardboard container (8 cm indiameter and 10 cm in height) until emergence. Newlyemerged parasitoids were used to create new adultcontainers with approximately 100 parasitoids, at a sexratio of approximately 2:1 (female: male). Prior toexperiments, E. puttleri were cultured for approxi­mately three generations (about 3.5 months) in thelaboratory (Acosta, 1998).

Fifteen 3-day-old mated females from each popula­tion were held individually in plastic petri dishes (9 cmin diameter). Each population was kept in a growthchamber (60-70% RH range, photoperiod of 16:8 (L:D»set at 15, 24, and 30°C, respectively. Each day, a single,24-h-old Colorado potato beetle egg mass (=22 eggs/mass) was provided to each female. A cotton rollsaturated with a 1:4 honey-water solution was pro­vided every other day. Egg masses were changed dailyand placed individually in a 5-mm3 cotton-stopperedplastic vial for subsequent measurements and adultparasitoid emergence. For each female, longevity (adultemergence to death), preoviposition period (emergenceto first oviposition), oviposition period (first to lastoviposition), parasitism rate (average proportion ofeach egg mass parasitized), total eggs per female(number hosts parasitized per egg mass), eggs perfemale per day (total eggs/oviposition period), imma­ture development time (oviposition to adult emer­gence), and average emergence percentage (number

emerged adults/number parasitized eggs per egg mass)were measured at three temperatures for each popula­tion. Successful oviposition and parasitism were judgedby observation of parasitoid pupa within individualeggs. No estimate of host egg killing (see Corrigan andLashomb, 1990) was made.

The experiment was repeated for three adult genera­tions kept at 24 and 30°C.Alow emergence rate at 15°Cin the first generation precluded measurement ofsubse­quent generations at this temperature. Females usedin the second and third generations were selected fromthose emerging approximately halfway through theprevious generation. Mean longevity was calculatedusing all females assigned to each population, genera­tion, and temperature. For all the other adult character­istics, only those females that produced eggs wereincluded in data analysis.

Life table statistics were estimated for females ateach temperature, population, and generation. Netreproductive rate, the intrinsic rate ofnatural increase,mean generation time, and doubling time, were calcu­lated as described by Ricklefs (1979), Price (1984), andWeidenmann and O'Neil (1990). Net reproductive rate(Ro) was calculated as R o = I lx . mx, where lx is the agespecific survivorship and m x is the number ofdaughtersproduced per female. The intrinsic rate of naturalincrease (rm) was calculated as rm = In RJT, where Tisimmature developmental time. Doubling time (t) wascalculated as t = In 2/rm. Life history characteristics ofparasitoids collected from Honduras were compared tosimilar measures of life history characteristics of E.puttleri from Colombia and Mexico (Obrycki et al.,1987; Ruberson et al., 1987, 1989). Comparisons weremade for life history characteristics measured at 24°C.

To test for significance across generations, a split­split-plot analysis ofvariance (ANOVA) was performedusing temperatures as main plots, populations as asub-plot, and generations as sub-sub-plots. Within gen­erations, a split-plot ANOVA was performed usingtemperature as a main plot and population as a sub­plot. Prior to ANOVA, each variable was tested fornormality and homogeneity ofvariance. When a trans­formation was indicated, a Box-Cox procedure wasused to determine the most appropriate transformation(Montgomery, 1991). Transformations used were arcsinfor emergence percentage and female percentage and10glO for longevity, preoviposition period, immaturedevelopment, and eggs/day. All the statistics wereevaluated at the ex = 0.05 level of significance. Allstatistical analyses were conducted using SAS (1985)software programs.

RESULTS

Mean female longevity ranged from 9.7 to 54.3 days(Table 1). First generation females reared at 15°C lived

Edovum LIFE HISTORY 83

TABLE 1

Adult Life History Characteristics (Mean::!: SEM) ofThree Populations ofEdovum puttleri

First generation (N = 15)" Second generation (N = 10) Third generation (N = 10)b

Characteristics River Marcala LaPaz River Marcala LaPaz River Marcala LaPaz

15°C

Female longevity (days)' 45.7:!: 10.2 54.3 :!: 5.99 46.3 :!: 8.26Preoviposition period (days)' 8.2:!: 1.49 13.3:!: 1.25 1O.2:!: 1.45Oviposition period (days)' 36.0:!: 6.68 25.5:!: 2.64 29.2 :!: 4.78Parasitism (%), 16.3:!: 1.91 16.6:!: 0.98 15.6:!: 1.32Total eggs/female' 124.0 :!: 21.6 90.9:!: 11.4 96.6:!: 15.1Eggs/female/daY' 3.4 :!: 0.40 3.5 :!: 0.21 3.3 :!: 0.28

24"C

Female longevity (days) 16.8:!: 1.87 15.4 :!: 2.33 14.3:!: 1.42 36.9::':: 5.27 31.1 :!: 5.04 33.9 :!: 4.03 33.5 :!: 9.13 37.4 :!: 3.81 32.1 :!: 5.12Preoviposition period (days) 4.5 :!: 0.24 4.8:!: 0.28 5.6:!: 0.61 4.1 :!: 0.22 4.5::':: 0.22 5.6::':: 0.92 5.7 :!: 0.87 4.6 :!: 0.16 4.3 :!: 0.24Oviposition period (days) 14.0:!: 1.87 13.6 :!: 2.23 10.5:!: 1.59 24.4 :!: 2.62 19.8::':: 2.87 22.7 :!: 2.39 21.2 :!: 4.13 26.6::':: 2.16 23.7 :!: 2.78Parasitism (%) 32.3::': 2.54 32.9::': 2.39 30.1 :!: 2.12 43.8::':: 3.99 45.2::':: 2.04 46.8::':: 2.41 46.2::':: 3.01 43.3::':: 2.47 45.5 :!: 4.74Total eggs/female 104.0::': 16.9 98.6::': 16.5 76.3:!: 12.6 240.1::':: 28.1 201.7 ::':: 31.5 233.1::':: 25.7 205.1::':: 40.3 239.9::':: 19.5 238.3 :!: 31.1Eggs/female/day 7.1::': 0.57 7.2::': 0.53 6.6::': 0.47 9.5::':: 0.97 9.8::':: 0.41 10.1 :!: 0.48 9.4 ::':: 0.60 9.1 ::':: 0.48 9.4 :!: 0.99

30°C

Female longevity (days) 9.7:!: 1.88 12.4 :!: 1.42 11.0:!: 1.95 14.0 :!: 2.25 20.6 :!: 3.56 19.6::':: 2.11 12.7 :!: 2.10 20.9:!: 2.67 17.8::':: 3.65Preoviposition period (days) 4.6 :t 0.54 4.3 :t 0.13 4.5 :!: 0.13 4.4 :!: 0.22 4.3::':: 0.21 4.2 :!: 0.13 4.6::':: 0.26 4.6::':: 0.18 4.0 :!: 0.01Oviposition period (days) 8.2:!: 1.86 9.8:!: 1.37 8.6:!: 1.81 11.5 ::':: 1.83 17.0 :!: 2.54 16.3::':: 1.46 11.5 :!: 1.66 15.0:!: 2.78 14.2 :t 2.96Parasitism (%) 36.4 :t 4.20 28.7 :!: 3.66 27.6 :t 3.48 26.9:!: 2.94 32.0::':: 3.48 38.0::':: 2.26 23.4 :!: 2.34 25.3 :!: 3.35 25.6 :t 2.64Total eggs/female 66.5:!: 16.3 63.1 :t 12.5 44.8:t 8.28 67.1::':: 12.8 111.4 :!: 12.9 130.8 :!: 8.08 57.4 ::':: 7.95 86.4 :!: 21.5 83.89 :!: 21.2Eggs/female/day 8.0 :!: 0.92 6.3 :!: 0.81 6.1 :!: 0.77 5.9 :!: 0.65 7.0::':: 0.74 8.3 ::':: 0.51 5.1 :!: 0.46 5.3 :!: 0.69 5.4:t 0.56

a For all characteristics except longevity, data are reported for only those females that laid eggs. In the first generation N at 15, 24 and 30°C;River = 9, 15, 13; Marcala = 14, 14, 14; La Paz = 14, 15, 15; respectively.

b In the third generation N at 24 and 30°C; River = 9,8; Marcala = 10,9; La Paz = 9,9.C Not measured for second and third generations at 15°C. See text for details.

longer than females reared at 24 and 30°C (F = 42.37;df = 2, 126; P = 0.0001). Second and third generationfemales reared at 24 and 30°C lived longer thanfemales reared in the first generation at the sametemperatures (F = 22.55; df = 2, 192; P = 0.0001). Fe­males at 24°C lived longer than females at 30°C(F = 34.38; df = 1, 192; P = 0.0001). There was nosignificant difference in longevity among populationseither within temperatures or among generations(F = 2.56; df = 2, 192; P = 0.0796).

On average, the preoviposition period ranged from4.0 to 13.3 days (Table 1). First generation females hada longer preoviposition period at 15°C than at 24 and30°C (F = 59.85; df = 2, 114; P = 0.0001). For subse­quent generations, females at 24°C had a longer preovi­position than females at 30°C (F = 6.80; df = 1, 182;P = 0.0099). First generation females from River had ashorter preoviposition period than females from Mar­cala and La Paz (F = 3.94; df = 2, 114; P = 0.0222). Forsubsequent generations there were no significant differ­ences among populations (F = 0.03; df = 2, 182;P = 0.9703).

Oviposition period ranged from 8.2 to 36.0 days(Table 1). Females reared at 15°C oviposited overlonger periods than females reared at 24 and 30°C(F = 44.84; df = 2, 114; P = 0.0001). Second and third

generation females had a longer oviposition periodthan first generation females (F = 28.81; df = 2, 182;P = 0.0001). For all generations, females reared at24°C had longer oviposition periods than females rearedat 30°C (F = 43.63; df = 1, 182; P = 0.0001). Therewere no significant differences in oviposition periodsamong populations within temperatures or among gen­erations (F = 0.95; df = 2, 182; P = 0.3904).

The percentage of eggs parasitized ranged from 15.6to 46.8 (Table 1). Parasitism during the first generationwas lower in females reared at 15°C than at 24 and30°C (F = 27.99; df = 2, 114; P = 0.0001). Also, para­sitism was lower in the first generation than in thesecond and third generations (F = 8.89; df = 2, 182;P = 0.0002). Within generations, females reared at24°C had higher parasitism rates than females rearedat 30°C (F = 55.71; df = 1, 182; P = 0.0001). Therewere no significant differences in parasitism ratesamong populations within temperatures or among gen­erations (F = 0.16; df = 2, 182; P = 0.8505).

On average, total eggs per female ranged from 44.8 to240.1 (Table 1). Egg production in the first generationwas higher for females reared at 15 and 24°C than forfemales reared at 30°C (F = 7.02; df = 2, 114;P = 0.0013). Total eggs per female was lower in the firstgeneration than in the second and third generations

84 ACOSTA AND O'NEIL

TABLE 3

Offspring Life History Characteristics ofThree PopulationsofEdouum puttleri

a For all characteristics except longevity, data are reported for onlythose females that laid eggs. In the first generation N at 15, 24, and30°C; River = 9, 15, 13; Marcala = 14, 14, 14; La Paz = 14, 15, 15.

b Characteristics not measured at 15°C for second and thirdgeneration. See text for details.

c In the third generation N at 24 and 30°C; River = 9, 8: Marcala =10, 9; La Paz = 9, 9.

Developmental time (days) 39.7:!: 1.23 38.4:!: 0.86 39.1 :!:: 0.69Emergence (%) 15.5 :!:: 6.96 9.9:!: 4.12 13.9:!:: 3.99Percentage of females 60.5:!:: 11.8 67.4 :!:: 12.0 62.9:!: 8.82

24°C

Developmental time (days) 18.5 :!:: 0.14 18.4 :!:: 0.21 18.4 :!:: 0.19Emergence (%) 76.7:!: 5.89 79.6:!: 2.19 84.9:!: 2.16Percentage offemales 75.1 :!:: 5.03 55.7 :!:: 7.02 71.3 :!:: 6.49

30°C

LaPazMarcalaRiver

First generation (N = 15)a

15°C

Characteristics

Developmental time (days) 11.9 :!:: 0.05 12.0:!:: 0.05 12.1 :!:: 0.07Emergence (%) 84.4:!: 3.93 85.7:!: 1.88 80.8 :!:: 3.10Percentage of females 70.1 :!:: 6.67 62.1 :!:: 9.26 82.8 :!:: 1.79

Second generation (N = 10)b

24°C

Developmental time (days) 17.7:!:: 0.11 16.9:!:: 0.11 16.7 :!:: 0.11Emergence (%) 93.7 :!:: 0.63 95.2 :!:: 0.77 93.5:!: 1.06Percentage offemales 64.3:!: 11.1 51.6 :!:: 8.39 43.6:!: 11.4

30°C

Developmental time (days) 12.1 :!:: 0.09 12.1 :!:: 0.09 12.2 :!:: 0.08Emergence (%) 84.1 :!:: 2.31 89.1 :!:: 1.53 87.9 :!:: 1.61Percentage offemales 72.2 :!:: 8.30 75.1 :!:: 7.29 86.0:!:: 1.52

Third generation (N = lOY

24°C

Developmental time (days) 16.7:!:: 0.08 15.9:!:: 0.06 16.4 :!:: 0.09Emergence (%) 94.9:!: 0.61 91.9 :!:: 0.70 93.7 :!:: 0.91Percentage of females 71.1 :!:: 9.70 72.4 :!:: 5.12 70.4 :!:: 7.19

30°C

Developmental time (days) 12.2 :!:: 0.13 12.1:!:: 0.06 12.0:!:: 0.04Emergence (%) 81.3 :!:: 3.96 88.0 :!:: 1.88 87.4 :!:: 1.30Percentage offemales 58.3:!: 12.8 66.0:!:: 9.69 76.3 :!:: 4.49

(F = 30.60; df = 2, 182; P = 0.0001). Females at 24°Cproduced more eggs than females at 30°C (F = 77.58;df = 1, 182; P = 0.0001). There were no significantdifferences in total egg production among populationswithin temperatures or among generations (F = 0.68;df = 2, 182; P = 0.5080). While in general, no signifi­cant differences in total egg production was foundamong populations, a Freidman's rank test showedsignificant differences in the frequency of total eggproduction among populations (X2 = 7.78; df = 6;P < 0.001). Females from the River site had the highestnumber offemales producing at least 125 eggs (Table 2).

Number ofeggs per female per day ranged from 3.3 to10.1 (Table 1). In the first generation, the number ofeggs per day was lower for females reared at 15°C thanfor females reared at 24 and 30°C (F = 30.58; df = 2,114; P = 0.0001). Daily egg production was lower in thefirst generation than in the second and third genera­tions (F = 8.31; df = 2, 182; P = 0.0001). For all genera­tions, females reared at 24°C produced more eggs perday than females reared at 30°C (F = 48.21; df = 1,182; P = 0.0001). Among populations there were nosignificant differences within temperatures or amonggenerations (F = 0.13; df = 2, 182; P = 0.8790).

The time required to complete immature develop­ment ranged from 11.9 to 39.7 days (Table 3). In thefirst generation, immatures reared at 15°C took longerto develop than immatures reared at 24 and 30°C(F = 3120; df = 2,231; P = 0.0001). Immature develop­ment was slightly but significantly faster in the secondand third generation than in the first generation(F = 130.34; df = 2, 503; P = 0.00017). Among genera­tions immature development was faster at 30 than at24°C (F = 9972.39; df= 1, 503; P = 0.0001). Femalesfrom the River site took slightly more time to developthan females from La Paz and Marcala (F = 9.94;df = 2,503; P = 0.0001).

The percentages of adults emerging varied from 9.9to 95.2 (Table 3). During the first generation theemergence was lower at 15°C than at 24 and 30°C

TABLE 2

Frequency of Total Egg Production for Female Edouumputtleri Collected from Three Sites in Honduras, Reared at15°C, First Generation

Number offemales

Eggs per female River Marcala LaPaz

0 1 2 326-50 1 1 051-75 0 0 176-100 0 5 3

101-125 1 3 3126-150 1 2 2

>150 5 1 2

(F = 202.47; df= 2,114; P = 0.0001). Emergence waslower during the first generation than in the subse­quent generations (F = 14.97; df = 2,182; P = 0.0001).Among generations, the percentage of emergence washigher at 24 than at 30°C (F = 10.78; df = 1, 182;P = 0.0012). Among populations, no significant differ­ences were found in percentage of emergence acrosseither temperatures or generations (F = 0.99; df = 2,182; P = 0.3730).

On average, the percentage of females emerging

Edovum LIFE HISTORY 85

TABLE 5

Temperatures

Life Table Parameters of Three Populations of Edovumputtleri Reared on Colorado Potato Beetle Eggs at ThreeTemperatures

30°C

Second generation (n =' 10)

0.17 133.6 28 4 0.16 42.1 24 4.50.17 101.3 27 4 0.17 79.9 26 40.14 81.9 33 5 0.18 98.4 26 4

Third generation (n =' 10)

0.13 135.6 39 6 0.14 32.5 25 5.30.15 155.8 34 5 0.15 55.7 26 4.50.15 158.8 34 5 0.16 52.1 24 4.3

First generation (n =' 15)

0.03 6.00 59 23 0.12 61.6 36 6 0.14 40.5 27 50.03 3.93 54 27 0.11 40.6 33 6 0.15 27.8 22 50.04 7.50 56 19 0.12 46.8 33 6 0.13 30.2 27 6

RiverMarcalaLaPaz

RiverMarcalaLaPaz

RiverMarcalaLaPaz

a rro, intrinsic rate of increase.b Ro, net reproductive rate.c T, mean generation time (days).d t, doubling time for population (in days).

ranged from 43.6 to 86.0 (Table 3). In the first genera­tion, no significant differences in sex ratios were foundamong temperatures (F = 0.37; df = 2, 109;P = 0.6950), and unlike other life history characteris­tics, no significant differences were found across genera­tions (F = 0.61; df = 2, 182; P = 0.5462). However,among generations the percentage offemales emergingwas lower at 24 than at 30°C (F = 4.38; df = 1, 181;P = 0.0378). Among populations no significant differ­ences were found in percentage of females emergingacross either temperatures or generations (F = 1.19;df = 2, 181; P = 0.3056).

Significant interactions between treatment effectswere found (Table 4). In general, significant interac­tions between generations and other treatment effects(e.g., populations and temperatures) were most com­monly noted. For interactions including populations,only preoviposition and developmental time estimateswere affected. Only developmental time showed signifi­cant interactions among all three effects (populations,temperature, and generation).

The net reproductive rate (Ro) ranged from 3.93 to158.8 (Table 5). Parasitoids from River and La Paz hadhigher Ro values than parasitoids from Marcala. Thehighest Ro was found at 24°C. An increase in Ro wasobserved across generations at 24 and 30°C. The intrin­sic rate of natural increase (rm) ranged from 0.03 to

TABLE 4

a For a complete listing of the significance of all the interactions,see Acosta (1998).

ANaVA Results of Significant Interactions in the LifeHistory Characteristics of E. puttleri Reared at Three Tem­perature and Three Generations (Significance Judged atP = 0.05)0

0.18. Higher intrinsic rates were seen at 24 and 30°Cthan at 15°C. In general, parasitoids from La Pazshowed the highest rm' Overall, a small increase in rm

was observed across generations. Generation time (T)ranged from 22 to 59 days. Parasitoids from the Riversite tended to have the longest generation times. Gen­eration time decreased when the temperature in­creased. Doubling time (t) fluctuated between 4 and 27days. More time was required at 15°C to double thenumber of parasitoids and no major difference wasobserved among populations and across generations.

The life history characteristics ofE. puttleri reared at24°C from Honduras differed from those of Colombiaand Mexico (Table 6). Females from Honduras laidfewer eggs and lived 10 to 20 days less than femalesfrom Colombia and Mexico, respectively. Populationsfrom Colombia and Mexico were more female biasedthan populations from Honduras.

DISCUSSION

There is mixed evidence for the existence of biotypesof E. puttieri. Life history characteristics of the threeHonduran populations were similar under each tem­perature regime, suggesting that there are not distinctclimatic biotypes there. However, when populations ofE. puttieri collected in Honduras were compared withpopulations collected from Colombia and Mexico, abroader range in life history characteristics was evi-

pdfFCharacteristics

Developmental time

Preoviposition period (days)Developmental time

First generation; 15, 24, and 30°C

Temperature' PopulationPreoviposition period (days) 3.50 4,114 0.0099

Three generations; 24 and 30°C

Temperature' Population9.90 2,503 0.00013.28 2,181 0.0397

Temperature' Generation3.11 2,182 0.0470

15.03 2,182 0.00017.12 2,182 0.0011

12.83 2,182 0.0001160.13 2,503 0.0001

9.85 2,182 0.00015.05 2,181 0.0073

Population' Generation3.02 4,182 0.01933.11 4,503 0.0150

Temperatures' Populations' Generations3.90 4,503 0.0039

Developmental timeFemales(%)

Oviposition period (days)Parasitism (%)Thtal eggs/femaleEggs/female/dayDevelopmental timeEmergence (%)Females (%)

86 ACOSTA AND O'NEIL

TABLE 6

Comparison of the Life History Characteristics of ThreePopulations ofEdovum puttleri Collected in Three Countriesand Reared at 24°C and Photoperiod 16:8 (L:D)

Range of Mean::':: SEMmeans

Characteristics Hondurasa Colombiab Mexico

Female longevity (days) 31.1-37.4 49.1::':: 2.79 59.4 ::':: 4.90Preoviposition period (days) 4.1--4.7 4.1::':: 0.21 3.3::':: 0.49Oviposition period (days) 19.8-26.6 23.3::':: 0.84 25.9::':: 0.76Eggs attacked/mass (%) 43.3-46.8 40.6c 43.8c

Eggs/female/day 9.1-10.1 10.7::':: 0.51 11.1::':: 0.60Developmental time 15.9-17.7 15.2::':: 0.2 14.8::':: 0.1Survival (proportion) 0.92-0.95 0.94::':: 0.01 0.90::':: 0.02Females (%) 43.6-72.4 80.7::':: 2.39 81.0::':: 3.14

a Data are from the second and third generation. Characteristicsfrom the first generation were consistently significantly differentfrom subsequent generations and were not used in the comparisons(see text for details).

b Data from Colombia and Mexico are from Ruberson et at. (1987)for eggs attacked/mass, eggs/female/day, and emergence. Femalelongevity, preoviposition period, oviposition period, and percentage offemales are from Ruberson et at. (1989). Developmental time is fromObrycki et at. (1987). All characteristics from Colombia and Mexicowere measured using 24-h-oldL. decemlineata eggs.

c No SEM given.

dent. The similarity in the Honduran collections sug­gests that they represent a single population dispersedamong sites separated by at least 140 Km. The verifica­tion of the unity of this population awaits geneticanalysis of individuals among "sub-populations" andstudy ofthe distribution and phenology ofLeptinotarsaand other potential hosts. However, if verified, theexistence of a single population in western Honduraswould have important ramifications for the use of E.puttleri in biological control. Future collections for E.puttleri biotypes would have to range farther andhigher than ours, potentially collecting from popula­tions separated by hundreds ofkilometers or thousandsof meters. While E. pulleri populations from Mexico,Colombia, and Honduras do show differences, it wasthe ineffectiveness of both the Colombian and theMexican "biotypes" under low temperatures (Lashombet al., 1985; Obrycki et al., 1985) that served in part as astimulus for the current research. The discovery of abiotype adapted to low temperature awaits better under­standing of the biogeography of E. puttleri, its hostsand host plants, and its metapopulation dynamics inLatin America.

Ifbiotypes ofE. puttleri adapted to low temperaturesare difficult to locate, an alternative approach could bethe artificial selection or bioengineering of individualsadapted to survive and reproduce under low-tempera­ture regimes. There are two pieces of evidence thatsuggest potential for success in such efforts. First, animprovement in most life history characteristics from

the first to subsequent generations, as well as thesignificance of interactions between treatments andgenerations (Table 4), suggests inadvertent selection inthe first generation. The reason for this may have beenthat in the first generation tested, parasitoids weretaken from a rearing room, whereas for subsequentgenerations, the parasitoids were taken from growthchambers in which the temperature was more stable.While this reinforces the importance of acclimatingparasitoids inside the chamber in which they are goingto be evaluated, it also illustrates the level ofvariabilityof E. puttleri life history characteristics. This variabil­ity could serve as the basis for selection of individualsto temperatures common to the growing seasons ofsolanaceous crops (e.g., Tauber and Tauber, 1972; Hoy,1988). Second, a significant proportion of females fromthe River population produced at least 125 eggs, whichwas approximately one-half the maximum averageproduced at 24°C (Tables 1 and 2). These resultssuggest that selection of females with higher reproduc­tive output at low temperatures could be achieved toimprove the parasitoid effectiveness in the field. Coinci­dentally, that the River site was the highest ofthe threetested suggests that ifartificial selection is used, it maybe more easily applied to populations collected at thehighest possible altitudes, irrespective of the existenceof"biotypes" at these elevations.

Finally the relative paucity of natural enemies ofColorado potato beetle (Hough-Goldstein et al., 1993),the lack of extensive foreign exploration (Logan et al.,1997), and the need to find management alternativesfor beetle control (e.g., see Whalon et al., 1993) recom­mends intensification of efforts to find, select, or de­velop natural enemies that can effectively control thebeetle under temperature cropping conditions. In thisregard, the current study has illustrated the need forfurther basic research into the ecology and genetics ofone parasitoid of the Colorado potato beetle. Similarcomments apply to the beetle's other natural enemies.

ACKNOWLEDGMENTS

We thank CliffSadof, Jeff Stuart, and Ronald Cave for their adviceduring the conduct and reporting of this research. We also thankRoger Ratcliffe USDAIARS for the use of the growth chambers.Thanks also go to John LaSalle of the International Institute ofEntomology, London, UK for identification of E. puttteri specimensand to Luis Canas and Ray Cloyd for statistical support. This isPurdue Agricultural Research Program Paper No. 15840.

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