PHYSIOLOGICAL ECOLOGY Life Table Studies of Elasmopalpus lignosellus (: ) on Sugarcane

HARDEV S. SANDHU,1,2 GREGG S. NUESSLY,1 SUSAN E. WEBB,3 1 1 RONALD H. CHERRY, AND ROBERT A. GILBERT Environ. Entomol. 39(6): 2025Ð2032 (2010); DOI: 10.1603/EN10038 ABSTRACT The lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) is an important pest of sugarcane (a complex hybrid of Saccharum spp.) in southern Florida. Repro- ductive and life table parameters for E. lignosellus were examined at nine constant temperatures from

13 to 36ЊC with sugarcane as the larval food source. The pre- and postoviposition periods decreased Downloaded from https://academic.oup.com/ee/article/39/6/2025/359113 by guest on 05 October 2021 with increasing temperatures and reached their minimums at 33 and 36ЊC, respectively. The ovipo- sition period was longest at 27ЊC. The mean fecundity, stage-speciÞc survival, stage-speciÞc fecundity, intrinsic rate of increase, and Þnite rate of increase were greatest at 30ЊC and decreased with increasing or decreasing temperature. The net reproductive rate was greatest at 27ЊC. The Logan-6 model best described the relationship between temperature and intrinsic rate of increase. The generation and population doubling times were longest at 13 and shortest at 33 and 30ЊC, respectively. The most favorable temperatures for E. lignosellus population growth were between 27 and 33ЊC. Life table parameters for E. lignosellus reared on sugarcane were greater than for the Mexican rice borer [Eoreuma loftini (Dyar) (Lepidoptera: )] reared on an artiÞcial diet at 30ЊC. The intrinsic rates of increase for the sugarcane borer [ saccharalis (F.) (Lepidoptera: Crambidae)] reared on sugarcane or corn were the same as for E. lignosellus reared on sugarcane at 27ЊC, but the net reproductive rate was four times higher for the former than the latter borer species.

KEY WORDS oviposition, fecundity, intrinsic rate of increase, net reproductive rate, Logan-6

Sugarcane (a complex hybrid of Saccharum spp.) is an tively (Sandhu et al. 2010). Dead heart symptoms are important crop grown in many southern temperate produced when larvae reach the center of the shoot and through tropical regions of the world (United States damage or sever the youngest leaves or apical meristem. Department of Agriculture [USDA] 2008). Florida, Nonlethal damage is caused when larvae only chew a few Louisiana, Texas, and Hawaii are the main sugarcane millimeters into the shoot evidenced by several symmet- producing states in the United States. Florida was the rical rows of holes revealed as the leaves emerge from the leading sugarcane producing state in the United States whorl. Larval feeding damage reduces plant stand and in 2008 with 401,000 acres of sugarcane valued at vigor, sugarcane photosynthesis, number of millable $398.9M (USDA 2008). The lesser cornstalk borer, Elas- stalks and sugar yield (Carbonell 1977). mopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae), Reproductive studies of the lesser cornstalk borer is a polyphagous, semisubterranean pest that is widely have been conducted on or southern distributed in United States and Central and South (Luginbill and Ainslei 1917, Dupree 1965), America (Heinrich 1956, Genung and Green 1965, (King et al. 1961), (Leuck 1967), and sugar- Chang and Ota 1987). Eggs are deposited mostly on the cane (Carbonell 1978). In all these studies, tempera- soil surrounding plants. Larvae bore into sugarcane ture and relative humidity were allowed to vary with stems below the soil surface and produce a silken tunnel the climatic conditions. Stone (1968) and Mack and at the entrance hole outward into the soil from which Backman (1984) reported the longevity and oviposi- they attack the plants, as well as rest, molt and pupate tion rates of E. lignosellus on an artiÞcial diet under (Schaaf 1974). E. lignosellus requires 548DD to complete controlled environmental conditions. However, quan- development on sugarcane with lower and upper devel- titative information on life table parameters, such as opmental thresholds estimated at 9.3 and 37.9ЊC, respec- intrinsic rate of increase (r), net reproductive rate ␭ (R0), Þnite rate of increase ( ), mean generation time 1 Everglades Research & Education Center, University of Florida, (T), and population doubling time (DT) was not pub- Institute of Food and Agricultural Services, 3200 E. Palm Beach Road, lished in their studies. Belle Glade, FL 33430. Life tables are powerful tools for analyzing and 2 Corresponding author, e-mail: hardy@uß.edu. understanding the impact of external factors such as 3 Entomology and Nematology Department, University of Florida, Institute of Food and Agricultural Services, P.O. Box 110620, Gaines- temperature on the growth, survival, reproduction, ville, FL 32611. and rate of increase of populations (Sankepe-

0046-225X/10/2025Ð2032$04.00/0 ᭧ 2010 Entomological Society of America 2026 ENVIRONMENTAL ENTOMOLOGY Vol. 39, no. 6

rumal et al. 1989). The intrinsic rate of increase can and were counted using a hand lens. Fecundity was vary with the larval host or diet (Carey 2003). For reported as the number of eggs deposited by an indi- example, female Helicoverpa assulta Guenee (Lepi- vidual female during her entire life period. Age-spe-

doptera: Noctuidae) reared as larvae on artiÞcial diet ciÞc female survival (lx, percentage of females alive at had signiÞcantly greater r values than females reared speciÞc age x) and age-speciÞc fecundity (mx, number as larvae on pepper (Capsicum frutescens L.) (Wang et of female offspring produced by a female in a unit of al. 2008). To predict the lesser cornstalk borer popu- time) were recorded for each day (x) they were alive.

lation parameters on sugarcane, it is important to study The lx and mx values were calculated using results from its life history on the same host. Development and the lesser cornstalk borer immature development, sur- survivorship rates for E. lignosellus reared on sugar- vivorship, and sex ratio studies conducted concur- cane at constant temperatures were determined in a rently under the same environmental conditions recent study (Sandhu et al. 2010). The purpose of this (Sandhu et al. 2010). Age speciÞc fecundity was cal- experiment was to measure the effect of a range of culated as (f/(m ϩ f)) ϫ n, where f ϭ number of constant temperatures on reproductive (preoviposi- females, m ϭ number of males, and n ϭ number of Downloaded from https://academic.oup.com/ee/article/39/6/2025/359113 by guest on 05 October 2021

tion, oviposition, postoviposition periods, and fecun- offspring. The lx and mx were calculated for each ␭ dity) and life table parameters (r, R0, ,T,and DT)of cohort of 10 females. Data from pairs of adults in which the lesser cornstalk borer reared on sugarcane. either of the sexes died before the start of egg depo- sition were excluded from data analysis. Age-speciÞc survivorship curves were constructed using l and m Materials and Methods x x values for cohorts at each temperature treatment. Reproductive Parameters. Preoviposition, oviposi- Life Table Parameters. The age-speciÞc life table tion, postoviposition periods, and fecundity for the method was used to calculate the life table parameters lesser cornstalk borer were determined at nine con- for the lesser cornstalk borer at each of tested tem- stant temperatures [13, 15, 18, 21, 24, 27, 30, 33, and peratures (Birch 1948). The intrinsic rate of increase 36ЊC(Ϯ0.05ЊC)] at 14:10 (L:D) and 65Ð70% RH in (r) was calculated through iteration of the Euler- Α -rx ϭ temperature controlled chambers to construct time- Lotka equation ( e lxmx 1). The lx and mx values ϭ speciÞc life tables. The range of tested temperatures were used to calculate the net reproductive rate (R0 Α was selected based on those experienced by lesser lxmx, mean number of female offspring/female) and ϭ Α Α cornstalk borer in sugarcane in southern Florida. the mean generation time (T (xlxmx)/ (lxmx), Adults were obtained from immatures reared on sug- mean age of the mothers in a cohort at the birth of arcane used for companion developmental studies female offspring). The values for r at each tempera- conducted at the same temperatures and relative hu- ture were used to calculate the Þnite rate of increase midity as indicated above (Sandhu et al. 2010). Larvae (␭ ϭ er, the number of times the population multiplies were reared on sugarcane shoots (variety CP 78Ð1628, in a unit of time) and population doubling time (DT ϭ 4Ð5 leaf stage) placed horizontally in plastic contain- ln (2)/r, the time required for the population to dou- ϫ ϫ ers (30 15 10 cm) with a thin layer of vermiculite ble). To compare the thermal sensitivities of r and R0, covering the base of each shoot with Þve shoots per we plotted the relative values of these alternative container. Pupae were collected from each plastic Þtness measures against the tested temperatures. The container and placed on moistened paper towels in relative values were calculated by dividing the calcu- petri dishes. Ten male:female pairs of newly emerged lated values of each parameter at each temperature by adults (Ͻ12 h old) were Þrst released into each of their respective maximum values. three oviposition cages (17 ϫ 17 ϫ 17 cm) for mating. Model Evaluation. A nonlinear distribution was ob- Adults were provided with a 10% honey solution for served when r was plotted against the temperature feeding, because sugarcane does not produce a food treatments. To Þnd an equation that best Þt the ob- source for adults. After 24-h, pairs were moved to served relationship between r and temperature, six transparent plastic cylinders (one pair per cylinder) nonlinear models [Brie`re-1, Brie`re-2, Logan-6, Lactin, (11 cm length and 5 cm diameter; Thornton Plastic Taylor, and polynomial (fourth order) models] pre- Co., Salt Lake City, UT) lined with tubular synthetic viously used by us (Sandhu et al. 2010) to describe stockinette (Independent Medical Co-Op, Ormond temperature dependent development of E. lignosellus, Beach, FL) as an oviposition substrate. Females prefer and by others (e.g., Roy et al. 2003, Bonato et al. 2007) rough, dry substrates for oviposition. We used stock- to describe similar population parameters were tested. inette because it was preferred by females over the The parameters of the nonlinear models were esti- Handy Wipes (The Clorox Co., Oakland, CA) used mated with the nonlinear regression model of Mar- by previous workers (e.g., Chalfant 1975). The 10 quardt (1963) using SAS (SAS Institute 2008). Sigma male:female pairs were organized as cohorts with Plot (Systat Software, Inc., San Jose, CA) was used to three cohorts (30 pairs) from each of three genera- plot the regressions of the nonlinear models. The mod- tions tested over time at each temperature. Adults els were evaluated based on the coefÞcient of deter- were observed daily to record the limits of the pre- mination (r2), the adjusted coefÞcient of determina- 2 2 oviposition, oviposition, and postoviposition periods. tion (r adj, a modiÞed r that adjusts for the number of The stockinette was replaced daily during oviposition explanatory terms in the model), the residual sum of periods. The orange-colored eggs were easily ob- squares (RSS), and the corrected Akaike Information

served against the white background of the material Criterion (AICC) (Burnham and Anderson 2004). The December 2010 SANDHU ET AL.: LIFE TABLE ANALYSIS OF E. lignosellus 2027

Table 1. Analysis of variance for effects of temp, cohort, and generation on reproductive parameters of E. lignosellus on sugarcane

Preoviposition Oviposition Postoviposition Fecundity Source df FPdf FPdf FPdf FP Model 80 249.20 Ͻ0.0001 80 593.49 Ͻ0.0001 80 439.28 Ͻ0.0001 80 523.10 Ͻ0.0001 Error 570 570 570 570 Temp. 8 236.10 Ͻ0.0001 8 579.60 Ͻ0.0001 8 395.10 Ͻ0.0001 8 457.80 Ͻ0.0001 Cohort 8 1.05 0.3511 8 0.19 0.8291 8 0.77 0.4640 8 2.15 0.2420 Generation 2 0.78 0.5881 2 0.18 0.9820 2 0.84 0.5380 2 3.04 0.1941 T ϫ C 64 0.69 0.9670 64 0.41 1.0000 64 0.51 0.9990 64 1.54 0.6412 T ϫ G 16 0.74 0.6421 16 0.69 0.5240 16 0.76 0.6120 16 2.15 0.3540 C ϫ G 16 1.02 0.3950 16 1.11 0.4520 16 1.25 0.4550 16 1.89 0.5411 T ϫ C ϫ G 128 0.89 0.5490 128 0.86 0.5131 128 0.78 0.6290 128 0.97 0.6242

F, df, and P values represent ANOVA of temp, cohort, and generation treatments within a reproductive stage (PROC MIXED; SAS Institute 2008). Downloaded from https://academic.oup.com/ee/article/39/6/2025/359113 by guest on 05 October 2021

2 2 r and r adj. indicate better Þts with higher values, position, periods, and fecundity. Daily values by co- whereas RSS and AICC indicate better Þts with lower hort were used for analysis of effects of temperature values. The corrected AIC value was calculated using and generation on lx and mx. The percentage of fe- the formula: males alive at age x (lx) was arcsine square root trans- formed for normality purposes before analysis and AIC ϭ n log(RSS/n) ϩ 2Kn/(n Ϫ K Ϫ 1) C retransformed for presentation purposes. The TukeyÕs honestly signiÞcant difference test (SAS Institute where n denotes the sample size; RSS denotes the ␣ ϭ residual sum of squares; K is the number of model 2008) was used for means separation with 0.05. parameters including an error item (namely the num- ber of free parameters in the model itself). The AICc Results was preferred over the AIC because of small sample size (n/K Ͻ 40) in this study, for which AICc is Reproduction. Temperature signiÞcantly affected recommended (Burnham and Anderson 2004). the lengths of the lesser cornstalk borer preoviposi- Statistics. PROC MIXED (SAS Institute 2008) was tion, oviposition, and postoviposition periods (Table used to analyze the variance because of the potential 1). Cohorts, generations, and the modeled interac- covariance structure associated with taking repeated tions were not signiÞcant sources of variation in the measures over time at each temperature. Normality of models for any of these periods. Therefore, data were the data were tested with the Shapiro-Wilk normality pooled across cohorts and generations to calculate test (Shapiro and Wilk 1965). The oviposition cages means for these periods. The mean preoviposition were treated as cohorts and replications through time period decreased with an increase in temperature were treated as generations for data analysis. Tem- from 9.7 d at 13ЊCto2.3dat33ЊC (Table 2). The mean peratures, cohorts, generations, and their interactions oviposition period was longest (5.6 d) at 27ЊC and were used in the analysis of variance (ANOVA) mod- decreased with an increase or decrease in temperature els. Generations were used as the repeated variable from 27ЊC. The postoviposition period became pro- and the cohorts were nested under temperature in the gressively shorter from a maximum at 13ЊC to a min- repeated measures statement. Several covariance imum at 36ЊC. structures were Þtted to the data. The unstructured Fecundity was also signiÞcantly affected by tem- covariance type Þt well and was used for the analysis perature (Table 1). Cohort, generation, and modeled (Littell et al. 1998). Data for each pair of adults were interactions were not signiÞcant sources of variation used for analysis of effects of temperature, cohort, and in the fecundity model. Therefore, the fecundity data generation for preoviposition, oviposition and postovi- were pooled across cohorts and generations to calcu-

Table 2. Mean (؎SEM) preoviposition, oviposition, postoviposition periods and fecundity for E. lignosellus on sugarcane under laboratory conditions

Temp (ЊC) Preoviposition (d) Oviposition (d) Postoviposition (d) Fecundity (eggs/female) 13 9.7 Ϯ 0.06 a 2.2 Ϯ 0.05 f 5.9 Ϯ 0.07 a 29.2 Ϯ 3.13 f 15 7.2 Ϯ 0.07 b 2.8 Ϯ 0.06 e 5.3 Ϯ 0.07 b 42.3 Ϯ 4.21 e 18 5.8 Ϯ 0.05 c 4.5 Ϯ 0.05 c 4.2 Ϯ 0.05 c 51.1 Ϯ 4.66 d 21 3.5 Ϯ 0.05 d 4.5 Ϯ 0.07 c 4.0 Ϯ 0.06 d 56.3 Ϯ 4.89 d 24 2.9 Ϯ 0.05 e 4.8 Ϯ 0.05 b 3.8 Ϯ 0.06 e 97.5 Ϯ 5.31 c 27 2.7 Ϯ 0.06 f 5.6 Ϯ 0.06 a 3.2 Ϯ 0.05 fg 158.4 Ϯ 6.14 a 30 2.5 Ϯ 0.06 g 4.5 Ϯ 0.05 c 3.3 Ϯ 0.05 f 165.3 Ϯ 6.52 a 33 2.3 Ϯ 0.05 h 3.2 Ϯ 0.05 d 3.1 Ϯ 0.07 g 110.2 Ϯ 5.07 b 36 4.4 Ϯ 0.07 d 2.8 Ϯ 0.06 e 2.5 Ϯ 0.05 h 62.3 Ϯ 4.22 d

Means within a column followed by the same letters are not signiÞcantly different (TukeyÕs test, ␣ Ͼ 0.05). 2028 ENVIRONMENTAL ENTOMOLOGY Vol. 39, no. 6 Downloaded from https://academic.oup.com/ee/article/39/6/2025/359113 by guest on 05 October 2021

Fig. 1a–i. Relationships between the adult age (d) and age-speciÞc survival lx (solid line) and age speciÞc daily fecundity mx (dashed line) for E. lignosellus at each temperature. late mean fecundity at each temperature. Fecundity cohort or generation (Table 1). The intrinsic rate of increased with an increase in temperature from 13 to increase (r) and the Þnite rate of increase (␭) both 27ЊC and decreased at 33 and 36ЊC (Table 2). Mean increased with an increase in temperature from 13 to fecundity ranged from 29.2 (13ЊC) to 165.3 eggs 30ЊC before starting to decrease at Ͼ33ЊC (Table 3). Њ Њ (30 C). The net reproductive rate (R0) was greatest at 27 C Life Table Parameters. Temperature had a signiÞ- (82.6). Comparing the relative values of r and R0 ϭ ϭ Ͻ cant effect on lx (F 50.19; df 8, 333; P 0.0001) versus temperature resulted in similar increases to ϭ ϭ Ͻ and mx values (F 16.05; df 8, 333; P 0.0001). Generations of lesser corn stalk borers and the mod- eled interactions did not provide signiÞcant sources Table 3. Life table parameters for E. lignosellus on sugarcane ϭ ϭ at nine constant temperatures of variation in the models for lx (F 0.52; df 2, 333; P ϭ 0.5972; F ϭ 0.75; df ϭ 16, 333; P ϭ 0.7384) or m (F ϭ Temp. x rR TDT␭ 0.13; df ϭ 2, 333; P ϭ 0.8805; F ϭ 0.26, df ϭ 16, 333, P ϭ (ЊC) 0 0.9984). Therefore, the data were pooled across gen- 13 0.0214 16.3863 130.6554 32.3840 1.0216 erations to calculate means for these periods. Both lx 15 0.0335 31.3734 102.7285 20.6620 1.0341 18 0.0403 23.1422 77.9978 17.2052 1.0411 and mx increased with an increase in temperature from 13 to 30ЊC and then decreased Ն33ЊC (Figs. 21 0.0519 17.8213 55.4920 13.3449 1.0533 24 0.0808 39.8398 45.6598 8.5773 1.0842 1aÐi). 27 0.1229 82.5841 36.0535 5.6413 1.1307 Data were pooled across generations (i.e., 90 dif- 30 0.1418 77.0883 30.7755 4.8898 1.1523 ferent pairs were pooled for each temperature, total 33 0.1313 37.5822 27.7046 5.2787 1.1403 36 0.0709 19.8828 42.1790 9.7709 1.0735 810 pairs) to calculate the life table parameters r, R0, ␭,T,and DT at each temperature, because preovipo- r, intrinsic rate of natural increase (female/female/d); R0, net repro- sition, oviposition, postoviposition, and fecundity ductive rate (female/female/generation); T, generation time (d); DT, were signiÞcantly affected by temperature, but not by pop doubling time (d); ␭, Þnite rate of increase (female/female/d). December 2010 SANDHU ET AL.: LIFE TABLE ANALYSIS OF E. lignosellus 2029

r and temperature for the lesser cornstalk borer on the sugarcane is presented in Fig. 3.

Discussion Reproduction. The values determined here for re- productive parameters on sugarcane fell mostly within the ranges of those determined for E. lignosellus on other crops. The mean (ϮSEM) preoviposition period found in this study (2.3 Ϯ 0.05 d at 33ЊCto9.7Ϯ 0.06 d at 13ЊC) is similar to the value of 2.8 d reported by Stone (1968) for E. lignosellus on an artiÞcial diet at Downloaded from https://academic.oup.com/ee/article/39/6/2025/359113 by guest on 05 October 2021 Fig. 2. Effect of temperature (ЊC) on E. lignosellus in- 27ЊC. The mean oviposition period on sugarcane Ϯ Њ Ϯ Њ trinsic rate of increase (r) and net reproductive rate (R0). (2.2 0.05dat13Cto5.6 0.06dat27C) was shorter than those reported on artiÞcial diets (10.4 d, Luginbill and Ainslei 1917; 11.8 d, Stone 1968; and maximum values, but the curve for r was shifted 6.4 d, Simmons and Lynch 1990), but within the range slightly to the right of the curve for R (Fig. 2). The 0 determined by Dupree (1965) on southern mean T decreased from the maximum at 13ЊC (130.7 d) to the minimum at 33ЊC (27.7 d) (Table 3). The (mean: 4.1 d, range 1Ð9 d). The 4.7 d postoviposition period reported by Leuck (1967) on soybean is con- population DT decreased from a maximum of 32.4 d at Ϯ 13ЊCtoalowof4.9dat30ЊC. sistent with that found on sugarcane (2.5 0.05 to Ϯ Model Evaluation. The Þtted coefÞcients and the 5.9 0.07 d). model evaluation parameters are presented in Table 4. Fecundity on sugarcane (29Ð165 eggs per female) In general, all the tested models showed satisfactory mostly fell within the range reported by others on 2Ͼ 2 Ͼ leguminous crops and artiÞcial diets. The lesser corn- Þtted results with r 0.9111 and r adj 0.8577. The polynomial (fourth order) model showed the better Þt stalk borer mean fecundity (number of eggs/female) 2 2 reported in earlier studies was 192 on cowpeas (Lug- to the data based on its higher r (0.9937) and r adj (0.9833) and lower RSS (0.0001) values than other inbill and Ainslei 1917), ranged from 124 to 129 on models. However, the greater number of Þtted pa- soybean (King et al. 1961, Dupree 1965, and Leuck rameters in the polynomial model resulted in greater 1967), and ranged from 67 (Calvo 1966) to 419.5 on AICc (Ϫ48.498) than the other tested models. Based artiÞcial diet (Stone 1968). The results of our study are on the lowest AICc (Ϫ62.981) values, the Logan-6 was similar to those of Mack and Backman (1984) who found to be the best model to describe the relationship reported an increase in fecundity with an increase in between r and temperature. The Þtted curve for the temperature from 17 to 27.5ЊC, peaks at 27.5 and Logan-6 model representing the relationship between 30.5ЊC, and large decreases at 17 and 35ЊC.

Table 4. Fitted coefficients and evaluation indices for six nonlinear models tested to describe the relationship between intrinsic rate of natural increase (r)ofE. lignosellus and temp

Nonlinear models Parameters Brie´re-1 Brie´re-2 Logan-6 Lactin Taylor Polynomial (fourth order) a (ϫ 10Ϫ5) 8.930 13.192 Ñ Ñ Ñ Ϫ0.4247 b (ϫ 10Ϫ3) ÑÑÑÑÑ 0.3487 c ÑÑÑÑÑ Ϫ0.0101 d 2.000 3.963 Ñ Ñ Ñ 0.1274 e ÑÑÑÑÑ Ϫ0.5725 mx Ñ Ñ 0.041 Ñ Ñ Ñ ␳ Ñ Ñ 0.180 0.006 Ñ Ñ ⌬ Ñ Ñ 5.498 1.836 Ñ Ñ Rm ÑÑÑÑ0.1330 Ñ T0 11.508 8.992 Ñ Ñ 6.909 Ñ Tm 36.894 36.095 37.225 40.499 Ñ Ñ Topt. ÑÑÑÑ29.664 Ñ ␭ Ϫ1.073 r2 0.9296 0.9584 0.9820 0.9499 0.9111 0.9937 2 r adj 0.8873 0.9168 0.9639 0.8997 0.8577 0.9833 RSS 0.0012 0.0007 0.0003 0.0008 0.0015 0.0001 Ϫ Ϫ Ϫ Ϫ Ϫ Ϫ AICC 62.721 55.464 62.981 53.779 60.622 48.498

a, b, c, d, e, empirical constants; mx, growth rate at given base temp; ␳, developmental rate at optimal temp; ⌬, no. of degrees over the base temp over which thermal inhibition becomes predominant; ␭, empirical constant which forces the curve to intercept the y-axis at a value below zero; Rm, is the max developmental rate; T0, lower temp threshold; Tm, upper temp threshold; Topt, optimum temp; Ñ, absence of coefÞcient 2 2 in the model; r , coefÞcient of determination; r adj, adjusted coefÞcient of determination; RSS, residual sum of squares; AICC, corrected Akaike Information Criterion. 2030 ENVIRONMENTAL ENTOMOLOGY Vol. 39, no. 6

on sugarcane. The results of Bessin and Reagan (1990) and Se´tamou et al. (2002), who found very different r and R0 values for D. saccharalis that developed on corn and sugarcane compared with an artiÞcial diet containing Ͻ10% sugarcane leaf sheathes, provides further evidence that larval host or diet effects the intrinsic rate of increase. In most ectotherms, r reaches its maximum value at

a greater temperature than for R0. Huey and Berrigan (2001) attributed this to the sensitivity of r (but not

R0) to the accelerating effect of high temperature on generation time. Because r is inversely related to gen-

eration time and R0 is independent of it (Cole 1954, Њ Downloaded from https://academic.oup.com/ee/article/39/6/2025/359113 by guest on 05 October 2021 Fig. 3. Relationship between temperature ( C) and in- Lewontin 1965), the normal shortening of the gener- trinsic rate of natural increase (r) for E. lignosellus on sug- ation time associated with rising temperatures will arcane described by the Logan-6 model. work to increase r without affecting R0. This leads to a shift to the right in the thermal Þtness curve for r

Life Table Parameters. E. lignosellus reached its relative to R0, as was observed in this study. This right maximum reproductive rate within the same temper- shift of the r curve relative to the R0 curve observed ature range where generation time and population for E. lignosellus on sugarcane may be because of the doubling time were the lowest (30Ð33ЊC). Life table shortest generation time occurring at a temperature Њ parameters for lesser cornstalk borer on other hosts is three and 6 C greater than the maximum r and R0 not available for comparison, but such values have values, respectively. been published for other stalk boring Lepidoptera Model Evaluation. The same mathematical models pests of monocots (Table 5). Life table parameters at used in the current study were also tested to describe 25ЊC on corn and artiÞcial diet for Diatraea lineolata the relationship between temperature and r for Tet- (Walker) (Lepidoptera: Crambidae), a neotropical ranychus mcdanieli McGregor (Acarina: Tetranych- cornstalk borer, were less than those found in this idea) and Stethorus punctillum Weise (Coleoptera: study for E. lignosellus that developed as larvae on Coccinellidae) on red raspberry (Rubus idaeus L.), sugarcane at 24ЊC (Rodrõ´guez-del-Bosque et al. 1989). Sitotroga cereallela (Olivier) (Lepidoptera: Gelechi- The sugarcane borer, D. saccharalis (F.), and the Mex- idae) on corn (Zea mays L.), and Halyomorpha halys ican rice borer, Eoreuma loftini (Dyar) (both Lepi- (Stal) (Hemiptera: Pentatomidae) on green beans doptera: Crambidae), recorded lower r and ␭, and [Vigna radiata (L.) Wilczek] (Roy et al. 2003, Hansen higher T and DT parameters at 30ЊC on an artiÞcial diet et al. 2004, Nielsen et al. 2008). High r2 values were that included dried, ground sugarcane leaf sheaths used to choose the Lactin-2 model for T. mcdanieli and (Se´tamou et al. 2002) than those reported in our study the Brie`re-1 model for S. punctillum, S. cereallela, and for E. lignosellus. The Mexican rice borer had a slightly H. hays. In the current study, the polynomial (fourth

greater R0 than the lesser cornstalk borer that indi- order) provided the best Þt between temperature and 2 2 cates its high reproductive potential, but the r for the r based on r , r adj, and RSS. However, Angilletta Mexican rice borer was lower on an artiÞcial diet than (2006) reported that the selection of model based on for the lesser cornstalk borer on sugarcane. Our stud- r2 and RSS can be erroneous and AIC or AICc should ies determined that r and ␭ for E. lignosellus reared on be calculated to select the best model. The AIC mea- sugarcane were very similar to those for D. saccharalis sures the modelÕs ability to describe the data dis- reared on corn and on sugarcane at 27ЊC (Bessin and counted by the modelÕs complexity. Therefore, the Reagan 1990). However, the net reproductive rate Logan-6 model was the best to describe the relation-

(R0) for D. saccharalis on both of these host plants was ship between r and temperature. Additional factors approximately four times greater than for E. lignosellus such as soil moisture and natural enemies have been

Table 5. Life table parameters for selected stem-boring Lepidoptera pests of sugarcane and corn

Temp. Life table parameters Species (Lepioptera family) Food sources Reference (ЊC) ␭ rR0 TDT Diatraea lineolata (Crambidae) 25 Corn 0.053 15.6 51.5 Ñ 1.055 Rodrõ´guez-del-Bosque et al. 1989 Diatraea lineolata (Crambidae) 25 ArtiÞcial diet 0.054 19.9 55.4 Ñ 1.055 Rodrõ´guez-del-Bosque et al. 1989 Diatraea saccharalis (Crambidae) 30 ArtiÞcial dieta 0.059 12.0 42.0 11.7 1.06 Se´tamou et al. 2002 Diatraea saccharalis (Crambidae) 27 Corn 0.124 345.8 Ñ Ñ 1.132 Bessin and Reagan 1990 Diatraea saccharalis (Crambidae) 27 Sugarcaneb 0.124 332.9 Ñ Ñ 1.132 Bessin and Reagan 1990 Eoreuma loftini (Crambidae) 30 ArtiÞcial dieta 0.088 84.0 50.3 7.9 1.09 Se´tamou et al. 2002

␭ r, intrinsic rate of natural increase; R0, net reproductive rate; T, generation time (d); DT, pop doubling time (d); , Þnite rate of increase; Ñ values not available. a Including 6.25% by wt leaf sheaths of sugarcane variety CP 65Ð357. b Variety CP 61Ð37. December 2010 SANDHU ET AL.: LIFE TABLE ANALYSIS OF E. lignosellus 2031 reported to effect E. lignosellus populations under Calvo, J. R. 1966. The lesser cornstalk borer, Elasmopalpus Þeld conditions. For example, elevated moisture levels lignosellus (Zeller), and its control. Ph.D. dissertation, at the soil surface play an important role in reducing University of Florida, Gainesville, FL. oviposition and larval survival under Þeld conditions Carbonell, E.E.T. 1977. Morfologia del “barrenador menor (Smith and Ota 2002). Larval parasitoids and preda- de la cana de azucar” Elasmopalpus lignosellus (Zeller) tors may also play an important role in regulating E. (Lepidoptera: Phycitidae). Saccharum 5: 18Ð50. lignosellus population growth in sugarcane (Falloon Carbonell, E.E.T. 1978. Descripcion de danos causados por Elasmopalpus lignosellus (Zeller) en cana de azucar y de 1974). algunos de sus controladores biologicos. Saccharum 6: In conclusion, the life table analysis determined that 118Ð145. the lesser cornstalk borer has potential to quickly Carey, J. R. 2003. Longevity: the biology and demography of increase its population level in sugarcane. Tempera- life span. Princeton University Press, Princeton, NJ. tures in the range of 27Ð33ЊC were most favorable for Chalfant, R. B. 1975. A simpliÞed technique for rearing the reproduction and survival. The results of this temper- lesser cornstalk borer. J. Ga. Entomol. Soc. 10: 33Ð37. ature-dependent study on reproduction (preoviposi- Chang, V., and A. K. Ota. 1987. The lesser cornstalk borer: Downloaded from https://academic.oup.com/ee/article/39/6/2025/359113 by guest on 05 October 2021 tion, oviposition, postoviposition periods, and fecun- a new important pest of young sugarcane, pp. 27Ð30. In dity) and estimation of life table parameters provides Annual Report, 1986. Experiment Station. Hawaiian important information that will ultimately be used for Sugar PlanterÕs Association, Pahala, HI. predicting outbreaks of the lesser cornstalk borer and Cole, L. C. 1954. The population consequences of life-his- improving its management in sugarcane. Additional tory phenomena. Q. Rev. Biol. 29: 103Ð137. Dupree, M. 1965. Observations on the life history of the information is necessary to be able to predict E. lesser cornstalk borer. J. Econ. Entomol. 58: 1156Ð1157. lignosellus populations in the Þeld, including relation- Falloon, T. 1974. 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Berrigan. 2001. Temperature, demog- Nematology Department, University of Florida (UF), raphy, and ectotherm Þtness. Am. Nat. 158: 204Ð210. Gainesville, FL] and K. Pernezny (EREC, Belle Glade, FL) King, D. R., J. A. Harding, and B. C. Langley. 1961. for providing laboratory facilities for diet preparation. N. insects in Texas. Texas Agric. Exp. Stn. Misc. Publ. 550. Larsen and B. Thappa (EREC, Belle Glade, FL) assisted in Lewontin, R. C. 1965. Selection for colonizing ability, pp. collecting adult E. lignosellus to establish the insect colony. 77Ð94. In: H. G. Baker and G. L. Stebbins (eds.), The Statistical assistance was provided by M. Brennan and J. Genetics of Colonizing Species. Cambridge University Colee (Statistics department, UF, Gainesville, FL), and M. Press, Cambridge, MA. Josan and T. Lang (EREC, Belle Glade, FL). Sandeep Sandhu Leuck, D. B. 1967. Lesser cornstalk borer damage to peanut was instrumental in experimental set up and support. Support plants. J. Econ. 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