PHYSIOLOGICAL AND CHEMICAL ECOLOGY Determination and Consideration of Flight Potential in a Laboratory Population of True Armyworm (: )

LIZHI LUO,1, 2 S. J. JOHNSON,1, 3 A. M. HAMMOND,1 J. D. LOPEZ,4 J. P. GEAGHAN,5 4 4 K. R. BEERWINKLE, AND J. K. WESTBROOK

Environ. Entomol. 31(1): 1Ð9 (2002) ABSTRACT Flight potential, a poorly understood phenomenon in the migratory true armyworm, Pseudaletia unipuncta (Haworth), was investigated in a laboratory population using tethered-ßight techniques. True armyworm exhibited strong ßight potential relative to other known migratory noctuids whose ßight potentials were previously determined by similar techniques. Flight potential was generally low for 1-d-old and increased with age to day 5 of adult life. Flight speed and distance ßown decreased for female moths from day 5 to day 10as their reproductive system developed. The greatest average ßight speed, total ßight duration, and distance ßown was exhibited by 5-d-old females and 10-d-old males, suggesting that ßight potential may differ by sex. Ten-day-old moths had the longest ßight duration. Factor analysis showed that total ßight distance, total ßight duration, and average ßight speed are strongly correlated to the factor variable, but the correlation for longest ßight duration was weaker. The signiÞcance of these Þndings to migratory ßight and reproductive behavior of P. unipuncta is discussed in the light of published Þndings.

KEY WORDS Pseudaletia unipuncta, ßight potential, age, sex, tethered-ßight, migration.

INSECT FLIGHT POTENTIAL, a characteristic affecting in- Cooter 1991; Sappington and Showers 1991, 1992; Luo sect habitat persistence (Southwood 1962, 1977), is an et al. 1995; Akbulut and Linit 1999). important life history trait (Dingle 1985, 1996). It not Improved tethered-ßight techniques provide op- only allows adults to escape from a deteriorating hab- portunities to readdress ßight-related parameters. itat but also determines where and when their off- Does ßight duration adequately measure ßight poten- spring are produced (Dingle 1985, 1996). Its study tial, and if not, which parameter is better or how many therefore has been a major research focus for many parameters should be used to evaluate this trait? The migratory (e.g., Johnson 1969; Dingle 1985, age of maximum ßight propensity, as measured by 1996). However, our understanding is incomplete, tethered ßight, is generally assumed to correspond to even though signiÞcant advances have been made the migratory ßight period in the Þeld (Johnson 1969, through several decades of effort. For example, it has 1976). However, in some noctuids like the armyworm been generally accepted that ßight duration is an ex- (Walker) it occurs at 5Ð7 d after pression of ßight potential as determined by emergence when ovaries are maturing (Zhang and Li tethered-ßight or other similar techniques in the lab- 1985, Luo et al. 1995), and intensive ßight during this oratory (Dingle 1985, 1996). Improvements have been period greatly reduces this mothÕs reproductive po- made in tethered-ßight techniques (Cooter and tential (Luo et al. 1999). This suggests that migration Armes 1993, Beerwinkle et al. 1995). Also, other ßight of M. separata probably does not occur during this parameters such as speed, distance or numbers of period, and direct extrapolation of laboratory results ßights have been measured and used to judge the ßight to Þeld populations is therefore a problem at present. potential of (Zhang and Li 1985; Armes and Dingle (1985) suggested that insect ßight potential is a function of age. However, variation with age of noctuids has not been clearly shown because most 1 Department of Entomology, Louisiana Agricultural Experiment studies covered only a few days in the prereproductive Station, Louisiana State University Agricultural Center, Baton Rouge, period (Sharp et al. 1975; Zhang and Li 1985; Sapping- LA 70803. ton and Showers 1991, 1992). More intensive research 2 Current address: Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100094, P.R. China. is needed to advance our understanding of the nature 3 E-mail: [email protected]. of insect ßight potential, especially in relation to mi- 4 Area Wide Management Research Unit, Southern Plains gration. Agricultural Research Center, USDAÐARS, 2771F&BRoad, College The true armyworm, Pseudaletia unipuncta (Ha- Station, TX 77845. 5 Department of Experimental Statistics, Louisiana Agricultural Ex- worth), is a sporadic pest of and grasses periment Station, Louisiana State University Agricultural Center, Ba- in eastern North America (Breeland 1958, Guppy ton Rouge, LA 70803. 1961, Ayre 1985). The summer range of P. unipuncta

0046-225X/02/0001Ð0009$02.00/0 ᭧ 2002 Entomological Society of America 2ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 1 extends from the middle latitudes of the United States temperature is optimum for larval growth and devel- to Canada because it cannot survive summer temper- opment, and the photoperiod closely approximates atures in tropical or subtropical areas. In winter it is what P. unipuncta is exposed to in southern Texas conÞned to tropical or subtropical regions because it during the spring northward migration. Adults that cannot survive winter conditions in temperate areas emerged on the same day were transferred to a similar (Guppy 1961, 1969; Fields and McNeil 1984; Ayre jar in groups of Ϸ20and provided 5% honey solution 1985). In a study of the ßight periods of noctuid moths (vol:vol) ad libitum. Food was renewed daily. in western New York using blacklight traps, true ar- Voucher specimens are deposited in the Louisiana myworm moths generally appeared in relatively high State University Entomology Department Museum in numbers in April and May without a natural popula- Baton Rouge, LA. tion build-up, strongly suggesting migration (Chap- Tether Technique. A tethering procedure devel- man and Lienk 1981). Often these early-captured oped for testing the ßight behavior of M. separata (Luo moths appeared old because most forewing scales et al. 1995, 1999) was employed. Moths were anesthe- were lost, suggesting they had ßown in from southern tized individually for 5Ð7 s by placing each inside a latitudes. Direct evidence demonstrated that the true glass tube (2.2 by 9.5 cm) containing an ether-soaked armyworm could travel at least 1,300 km from Texas to cotton wick. The tether consisted of a 1.2 cm length Iowa during northward migration in spring (Hendrix inverted Y-shaped apparatus fabricated from a 0.25- and Showers 1992). Behaviorally and physiologically, mm-diameter copper wire. The insulation was re- the true armyworm has a relatively long prereproduc- moved from the forked end. This end was then at- tive period or precalling period closely associated with tached with a drop of Insta-Cureϩ glue (Bob Smith release of juvenile hormone (Cusson et al. 1990). Industries, Atascadero, CA) to the dorsal and lateral Duration of the prereproductive period, during which surface of the junction between the metathorax and migration occurs, is regulated by environmental cues the abdomen after the scales and hairs at the junction such as temperature and photoperiod (Turgeon and had been brushed away. The tethered- was held McNeil 1983, Delisle and McNeil 1986). Also, its re- in a 29.6-ml plastic cup until it was connected to the productive activity seems to be restricted before mi- arm of the ßight mill. The entire process took Ϸ2.5 gration because males do not respond to sex phero- min, which minimized trauma to the moth and made mone and females do not mate. These activities occur the use of a glue accelerator (Beerwinkle et al. 1995) after migration (McNeil 1986, 1987; unpublished unnecessary. In the case of M. separata (Luo et al. data). Information about ßight behavior and physiol- 1999), these techniques not only greatly reduced in- ogy of P. unipuncta is limited to the threshold tem- terference of the tether with normal functioning of the perature for take-off of the moth, around 10ЊC (Taylor wings or yaw during ßight, but also ensured that via- and Shields 1990), and a study demonstrating that lipid bility of the moths was not signiÞcantly different from is the major fuel during continuous ßight (Orchard et al. 1991). Thus, migratory ßight behavior and ßight untested moths. physiology are still poorly understood, and its ßight Flight Test. A 32-channel ßight mill system was behavior in relation to various physiological and eco- integrated with some recent advancements in elec- logical conditions has not been investigated. Here we tronic and computer technologies (Beerwinkle et al. report variation among individual true armyworms in 1995). The ßight mill arm was lengthened to a radius several ßight parameters and body measurements re- of 31.8 cm (2-m circumference) and counterweighted lated to age, sex and ovarian development following at the end opposite the tethered moth to balance the tethered ßight. This research is part of an intensive weight of the moth. Data were logged with an IBM study on the migratory ßight syndrome of the true AT-compatible microcomputer linked to all 32-ßight armyworm. mills through a 24-bit parallel digital input/output board. The ßight mills were located in a room where temperature, humidity, light intensity and photope- Materials and Methods riod were adjustable. The tethered-moths were pro- Insect and Rearing Conditions. True armyworm vided a piece of tissue paper to grasp when they were moths used for ßight tests were derived from the F8 connected to the ßight mill 30or 40min before each generation of a colony started with Þve pairs of moths test began. Data logging began at 1930hours in the captured from a light trap at New Madrid, MO (89Њ 42Ј evening and terminated at 0730 hours the next morn- W, 36Њ 24Ј N) in June 1994. Larvae were reared indi- ing (CST). Moths were tested only once. Temperature vidually on a modiÞed pinto bean diet (Shorey and and humidity in the ßight room were maintained at Hale 1965) at a temperature of 23 Ϯ 1ЊC and photo- 23 Ϯ 1ЊC and 70% Ϯ 10% RH. Light intensity was period of 12:12 (L:D) h in an environmental incubator. gradually decreased from 650Ð0.1 lux over a 30-min Pupae were kept in groups of 20in 3.78-liter opaque period after the test began, and a reverse process took plastic jars, about one quarter Þlled with vermiculite, place 30min before the test terminated. The 0.1-luxof and with strips of tissue hanging inside to provide a light intensity was maintained throughout the test resting site for the emerged moths. Pupae were kept period (Beerwinkle et al. 1995). Moths were excluded in the same environmental conditions as the larvae, from the data analyses if they were found detached and checked each morning for moth emergence. from the tether, had a broken wing or died during the These rearing conditions were chosen because the test period. However, only a few moths were detached February 2002 LUO ET AL.: FLIGHT POTENTIAL OF P. unipuncta 3 and only two of the moths (both 10-d-old) died during Table 1. Rotated factor pattern from factor analysis revealed the tests. two underlying factors among morphometric and flight variables measured on laboratory reared male and female P. unipuncta Determination of Body Weight, Dorsolongitudinal subjected to a 12-h tethered-flight test at 1–10 d after emergence Muscle Weight, and Reproductive Condition. Each moth was weighed before tethering. The dorsolongi- Factor loadings Variables tudinal muscle is the largest bundle of indirect ßight Factor 1 Factor 2 muscles in the thorax of lepidopterans. The muscle Body weight 0.18397 0.82683a was removed after drying the thorax of the moth at Dorsolongitudinal muscle weight 0.08112 0.87167a 50ЊC for 48 h. The dissected muscle was dried again at Longest ßight duration 0.6817a 0.05682 50ЊC to a constant weight. The reproductive condition Total ßight duration 0.83479a 0.25485 a of the female moth was characterized immediately Total ßight distance 0.95106 0.17729 Average ßight speed 0.81257a 0.07443 after the ßight test by measuring basal ovariole width, wet ovarian weight and mating status. The ovariole Loadings are the correlations between the original variables and the was measured at the widest point of the follicle at 50 factors (a loading of 0.707 corresponds to an R2 of 0.50). times using a dissecting microscope with an ocular a Important loadings for each factor. micrometer. Ovarian weight was taken after water on its surface was blotted with tissue paper. Ovarian weight as percent of female body weight was also geneous. Age treatments were not homogeneous. determined for all age groups. The mating status of PROC MIXED (SAS Institute 1992) was used to Þt females was determined by the presence or absence of different variances for the age treatments. Residuals spermatophores in the bursa, but the mating status of were Þtted with PROC MIXED under the assumption the males was not determined. of normality and analyzed with the Shapiro-WilkÕs Evaluation of Flight Potential. Several ßight param- statistic from PROC UNIVARIATE. The distributions eters were used to assess the ßight potential of true of most variables were fairly normal or symmetric armyworm moths, because, as noted and stressed else- making parametric analyses appropriate. The variables where, a single parameter might produce misleading Ôlongest ßight durationÕ and Ôßight speedÕ departed results or fail to reveal important ßight components from normality, and poisson distributions were Þtted (Dingle 1985). The Þrst parameter was the single long- to their variances with the GLIMMIX macro (SAS est continuous ßight, considered by some to charac- Institute 1992). All models were analyzed with PROC terize migratory ßight (Armes and Cooter 1991; Sap- MIXED to test for main effects and interactions. The pington and Showers 1991, 1992; Beerwinkle et al. Tukey-Kramer adjusted mean separation test was used 1995). The second was the total duration of ßight to determine signiÞcant differences among age groups summed over all bouts Ն10s. The third parameter both within and between the sexes for variables with measured was average ßight speed over the test pe- signiÞcant interactions, and within main effects for riod. Total ßight distance, an important estimate of variables without signiÞcant interactions (Saxton ßight potential of the tethered moth which has been 1998). ignored in most other tethered ßight studies, was also determined because it can help compensate for the Results shortcomings of total ßight duration and ßight speed (see discussion). Factor Analysis. The Þrst analysis included data for Flight Potential Determinants. Flight potential was both sexes on all variables except ovarian, and two determined as a function of age, testing 1-, 3-, 5-, 7- and factors accounted for 71.92% of the variation in the 10-d-old moths, rather than just the Þrst few days in data set. Results in the form of a rotated factor pattern the early stage of an adultÕs life, as is common in other (Table 1) show that the ßight variables constituted noctuid studies (Sharp et al. 1975; Sappington and one factor of similar behaving variables while the Showers 1991, 1992). Sex may inßuence ßight poten- morphometric variables constituted a second factor. tial in some noctuids (Sharp et al. 1975, Parker and The Þrst factor was best represented by total distance Gatehouse 1985, Sappington and Showers 1991) so we ßown with a loading or correlation (r) of 0.951. The compared the performance between sexes within the high loadings show that all the ßight values are same age and across all ages. strongly correlated to the factor variable except for the Statistical Analysis. Factor analyses (Johnson 1998) variable longest ßight duration. Longest ßight dura- were performed on the original variables to examine tion was the only one of the ßight variables with less the underlying relationships among them. One factor than half of the variation R2 ϭ .465 (loading 0.682) analysis was run for both sexes combined, but the accounted for in the analysis. The second factor is best ovarian variables were excluded. A second analysis represented by dorsolongitudinal muscle weight, al- was run for females only incorporating all variables, though when the analysis was run with the residuals including ovarian. Homogeneity of variance was the dorsolongitudinal muscle and body weight were checked with BartlettÕs test for all treatment combi- nearly equal with loadings of 0.8818 and 0.88145, re- nations, age by sex, sex alone and age alone. The spectively. The second analysis, performed on females hypothesis was not rejected, or barely rejected, for sex only and including all variables, revealed three factors treatments. With the large sample size available it was accounting for 80.93% of the variation in the data set decided that sex treatments were sufÞciently homo- (Table 2). The second and third factors correspond to 4ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 1

Table 2. Rotated factor pattern from factor analysis revealed three underlying factors among morphometric ovarian and flight variables measured on laboratory reared female P. unipuncta sub- jected to a 12-h tethered-flight test at 1–10 d after emergence

Factor loadings Variables Factor 1 Factor 2 Factor 3 Body weight 0.11133 0.18333 0.88381a Dorsolongitudinal muscle Ϫ0.38331 0.11911 0.77421a weight Longest ßight duration 0.21976 0.64838a 0.01561 Total ßight duration Ϫ0.05291 0.84805a 0.24205 Total ßight distance Ϫ0.09305 0.95307a 0.14727 Average ßight speed Ϫ0.16909 0.83267a 0.06143 Basal ovariole width 0.91851a 0.09746 Ϫ0.08747 Wet ovarian weight 0.97777a Ϫ0.06497 0.02456 Ovarian weight/body 0.96330a Ϫ0.10011 Ϫ0.14975 weight ϫ 100

Loadings are the correlations between the original variables and the factors (a loading of 0.707 corresponds to an R2 of 0.50). a Important loadings for each factor. the two factors generated from data for both sexes, except that the third factor was best represented by body weight rather than dorsolongitudinal muscle weight. The new factor was probably best represented by ovarian weight although all three ovarian variables had high loading and R2 values. Flight Potential. The true armyworm displayed high ßight capacity on the ßight mill system. Only 1.9% of females (n ϭ 158) and 4.8% of males (n ϭ 126) ßew Ͻ2 h, whereas 34.2% of the females and 19% of the males ßew Ͼ10h during the 12-h test period (Fig. 1A). Furthermore, Ͼ76% and 68.3% of females and males, respectively, ßew Ͼ6h.Sex(F ϭ 7.68; df ϭ 1, 274; P Ͻ Fig. 1. Frequency distribution of total ßight duration (A) 0.01) and age (F ϭ 12.4; df ϭ 4, 274; P Ͻ 0.0001) and longest ßight duration (B) as determined by tethered- ßight techniques in a laboratory population of P. unipuncta signiÞcantly affected total ßight duration of the moths, ϭ moths aged from 1 to 10d after emergence (shaded, female, but the interaction was not quite signiÞcant (F 2.19; n ϭ 158; open, male, n ϭ 126). df ϭ 4, 274; P ϭ 0.07). The average total ßight time of all female moths was 494.37 Ϯ 12.50min, and that of males was 442.1 Ϯ 14.13 min. Five-day-old moths had females ßew signiÞcantly further than the 1-, 3-, the longest average total ßight time and ßew signiÞ- and the 10-d-old females and all but 10-d-old males cantly longer than 3-d-old and 1-d-old moths (Fig. 2A). The total ßight time of one-day-old moths was (Fig. 3). Both sex (F ϭ 6.86; df ϭ 1, 274; P ϭ 0.009) and age signiÞcantly less than for the other four age groups. A ϭ ϭ Ͻ large proportion of moths had a low value for longest (F 4.20; df 4, 274; P 0.002) signiÞcantly affected ßight speed, and there was a signiÞcant interaction single ßight duration; 26.6% of females and 38.9% of ϭ ϭ ϭ males ßew Յ1 h and only 46.8% of females and 40.5% (F 2.52; df 4, 274; P 0.042). Flight speed of of males ßew Ͼ2 h (Fig. 1B). Sex (F ϭ 3.89; df ϭ 1, 274; 5-d-old females was the greatest (5.972 km/h) and was P ϭ 0.0495) and age (F ϭ 7.23; df ϭ 4, 274; P Ͻ 0.0001) signiÞcantly higher than that of 3- and 10-d-old fe- signiÞcantly affected the duration of the single longest males and 1- and 3-d-old males (Fig. 4). ßight, but there was no signiÞcant interaction (F ϭ Body and Dorsolongitudinal Muscle Weights. Sex ϭ ϭ Ͻ ϭ 1.29; df ϭ 4, 274; P ϭ 0.2729). The average single (F 133.73; df 1, 274; P 0.0001) and age (F 12.03; longest ßight of females was 155.74 Ϯ 9.81 min but only df ϭ 4, 274; P Ͻ 0.0001) affected body weight of the 126.36 Ϯ 11.19 min for males. The 10-d-old moths had moths (Fig. 5). There was a signiÞcant sex by age the highest average single longest ßight, which was interaction (F ϭ 4.99; df ϭ 4, 274; P ϭ 0.0007) due to signiÞcantly different from the other age groups (Fig. the dramatic increase in female weight from three to 2B). 5 d (Fig. 5). Five-, 7- and 10-d-old females were sig- Both sex (F ϭ 12.44; df ϭ 1, 274; P Ͻ 0.001) and age niÞcantly heavier than 1- and 3-d-olds and all males. (F ϭ 9.06; df ϭ 4, 274; P Ͻ 0.001) signiÞcantly affected There were no signiÞcant differences among the dif- the distance ßown by the moths on the ßight mill ferent male age classes (Fig. 5). Sex (F ϭ 10.61; df ϭ system. There was also a signiÞcant sex by age inter- 1, 274; P ϭ 0.0013) and age (F ϭ 5.6; df ϭ 4, 274; P ϭ action (F ϭ 2.79; df ϭ 4, 274; P ϭ 0.026). Five-day-old 0.0002) affected the weights of the dorsolongitudinal February 2002 LUO ET AL.: FLIGHT POTENTIAL OF P. unipuncta 5

Fig. 3. Flight distance of female and male P. unipuncta at different ages after emergence as determined by a 12-h teth- ered ßight test. Data are presented as mean Ϯ SE. Values within and between sexes associated with the same letter are not signiÞcantly different (␣ ϭ 0.05) as determined by a Tukey-Kramer adjusted means separation test. The sample sizes for females were 31, 27, 31, 33, 36, and for males 25, 31, 21, 23, 26, respectively, from left to right.

tion, average ßight speed and total distance ßown between the 10mated 7- and 10-d-oldßown females and the 59 virgin 7- and 10-d-old ßown females.

Discussion Our results show that P. unipuncta moths possess great ßight potential. Unlike most other species stud- Fig. 2. Total ßight duration (A) and longest ßight dura- ied (Johnson 1976, Dingle 1985, Parker and Gatehouse tion (B) during a 12-h tethered-ßight test for P. unipuncta at 1985, Sappington and Showers 1991), a majority of P. different days after emergence. Data are presented as unipuncta ßights were long, or at least not sharply mean Ϯ SE. Values associated with the same letter are not skewed toward short ßights (Fig. 1), even though we signiÞcantly different (␣ ϭ 0.05) as determined by a Tukey- tested moths as old as 10d. In other aspects of ßight Kramer adjusted means separation test. The sample sizes were 56, 58, 52, 56, and 62, respectively, from left to right. muscle of the moths, and the sex by age interaction was not signiÞcant (F ϭ 2.27; df ϭ 4, 274; P ϭ 0.061). Female muscle weight (5.461 Ϯ 0.051 mg) was sig- niÞcantly greater than that of males (5.208 Ϯ 0.058 mg) (Fig. 6). The dorsolongitudinal muscle of Þve- d-old moths was the heaviest (5.596 Ϯ 0.002 mg), and was signiÞcantly heavier than in 1-, 7- and 10-d-old moths (Fig. 6). Reproductive Status of Flown Female Moths. The three ovarian variables all increased linearly as the age of the ßown moths increased (Table 3). A signiÞcant age effect was detected for basal ovarian width (F ϭ 92.15; df ϭ 4, 153; P Ͻ 0.0001), wet ovarian weight (F ϭ 46.58; df ϭ 4, 153; P Ͻ 0.0001) and ovarian weight as a percent of female body weight (F ϭ 39.01; df ϭ 4, Ͻ Fig. 4. Flight speed of female and male P. unipuncta at 153; P 0.0001). None of the ßown females was mated different ages as determined by tethered ßight technique. until age 5-d and there was only one, six and four Data are presented as mean Ϯ SE. Values within and between females mated in the 5-, 7-, and 10-d-old female age sexes associated with the same letter are not signiÞcantly groups, respectively (Table 3). There was no statistical different (␣ ϭ 0.05) as determined by a Tukey-Kramer ad- difference in longest ßight duration, total ßight dura- justed means separation test (see Fig. 3 for sample sizes). 6ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 1

(recalculated from Sappington and Showers 1991), while that for P. unipuncta was 58.1% (n ϭ 31) and 4.55 km/h, respectively, using the same standard. Flight potential of P. unipuncta is very similar to that of M. separata, a well-known migratory noctuid, as de- termined by similar techniques (Zhang and Li 1985, Luo et al. 1995). The strong ßight potential of P. unipuncta is indic- ative of a migratory life history strategy, characteristic of many insects living in temporary or early succession habitats (Southwood 1962, 1977). Because the capac- ity to survive low and high temperatures is limited for this species (Guppy 1961, 1969; Fields and McNeil 1984; Ayre 1985) obligatory escape (in this case by ßight) from seasonal temperature extremes is ex- pected. The environmental conditions experienced by Fig. 5. Body weight of female and male P. unipuncta at the moths tested in this study may have been condu- different days after emergence. Data are presented as cive to high ßight potential, because under such rear- mean Ϯ SE. Values within and between sexes associated with ing conditions reproductive activity of P. unipuncta is the same letter are not signiÞcantly different (␣ ϭ 0.05) as relatively constrained (Table 3). Indeed, some of the determined by a Tukey-Kramer adjusted means separation 10-d-old females contained immature ovaries like test (see Fig. 3 for sample sizes). those of 2-d-olds or 3-d-olds (Table 3). Migratory ßight is favored in environments where reproductive activity is limited, but commencement of reproductive potential, our results are consistent with those of pre- activity may diminish the ßight potential of the moth, vious tethered-ßight studies of other migratory noc- as already demonstrated elsewhere (Sharp et al. 1975, tuids (Sharp et al. 1975; Zhang and Li 1985; Armes and Armes and Cooter 1991, Luo et al. 1995, Gatehouse and Cooter 1991; Sappington and Showers 1991, 1992; Luo Zhang 1995). et al. 1995). The black cutworm, Agrotis ipsilon Hufna- In our study, age was one of the major factors af- gel is a powerful migrant that has been conÞrmed to fecting ßight potential of P. unipuncta (Figs. 2Ð4). migrate over 1,000 km, and it appears synchronously These data were comparable to Þndings for a number with P. unipuncta in immigrant areas in the spring of species (Johnson 1969, 1976; Dingle 1985, 1996) (Hendrix and Showers 1992, Sappington and Showers including other noctuids (Sharp et al. 1975; Zhang and 1992). The ßight potential of P. unipuncta was equal to Li 1985; Armes and Cooter 1991; Sappington and or greater than that reported for A. ipsilon (Sapping- Showers 1991, 1992; Luo et al. 1995). Flight potential ton and Showers 1991, 1992). Sixty percent (n ϭ 20) of a migratory insect is generally low immediately after of 1-d-old A. ipsilon moths made a ßight of at least 1-h emergence and increases to a maximum at a relatively (Sappington and Showers 1992), and the average early stage of adult life and then declines with age ßight speed for 1- to 5-d-old adults was 3.88 km/h (Dingle 1985), or as ovaries develop (Johnson 1976). In our studies, P. unipuncta reached maximum ßight potential when 5 d old. In female moths there was a signiÞcant decline in ßight distance and ßight speed as the ovary continued to develop (Table 3) and the dorsolongitudinal muscle weight declined from 5Ð10d old (Fig. 6). However, there was not a signiÞcant decline in ßight potential of male moths from 5- to 10-d-old. The period of high ßight potential may have been extended by the fact that most of the 7- and 10-d-old moths did not mate (Table 3) under the rearing conditions provided. Although reproductive activities have a negative effect on ßight potential of other noctuids (Sharp et al. 1975, Armes and Cooter 1991, Luo et al. 1995, Gatehouse and Zhang 1995), mating did not affect the ßight potential of black cutworm (Sap- pington and Showers 1992). In our study, none of the ßight parameters was signiÞcantly different between 7- and 10-d-old mated and virgin females. Fig. 6. Dorsolongitudinal muscle weights of P. unipuncta at different days after emergence. Data are presented as Although it has generally been assumed that the mean Ϯ SE. Values associated with the same letter are not migratory period corresponds to the period when signiÞcantly different (␣ ϭ 0.05) as determined by a Tukey- maximum ßight potential is most likely to occur (John- Kramer adjusted means separation test (see Fig. 2 for sample son 1969, 1976) our results do not necessarily mean sizes). that the migratory period for P. unipuncta occurs be- February 2002 LUO ET AL.: FLIGHT POTENTIAL OF P. unipuncta 7

Table 3. Variation of ovarian development and mating status of female P. unipuncta subjected to a 12-hour tethered-flight test at different days after emergence

Basal ovariole Wet ovarian Ovarian weight/ No. of Age n width, mm weight, mg bodyweight ϫ100 females mated 1 31 0.229 Ϯ 0.008a 7.61 Ϯ 0.66a 3.76 Ϯ 0.30a 0 (0.18Ð0.36) (3.3Ð20.3) (1.72Ð9.42) 3 27 0.376 Ϯ 0.020b 17.87 Ϯ 2.47b 8.71 Ϯ 1.16b 0 (0.20Ð0.60) (6.1Ð51.8) (3.03Ð24.43) 5 31 0.408 Ϯ 0.023b 24.29 Ϯ 3.20c 10.31 Ϯ 1.43bc 1 (0.20Ð0.60) (5.7Ð73.9) (2.23Ð32.90) 7 33 0.453 Ϯ 0.025bc 37.39 Ϯ 4.16d 16.74 Ϯ 1.93cd 6 (0.22Ð0.60) (8.2Ð98.0) (3.10Ð37.23) 1036 0.529 Ϯ 0.015c 43.23 Ϯ 3.31d 19.22 Ϯ 1.61d 4 (0.32Ð0.60) (11.8Ð82.9) (5.18Ð37.10)

Mean Ϯ SE for body weight, basal ovariole width and ovarian weight. Means in a column sharing the same letter are not signiÞcantly different (␣ ϭ 0.05) as determined by the Tukey-Kramer adjusted mean separation test. Numbers in parentheses are extreme values. No statistical analysis was conducted on the mating status of females. yond 5 d after emergence. Two of the P. unipuncta actively seek females by searching for and tracking females caught in an immigrant population that most pheromone plumes. Thus, a high ßight potential at a likely migrated from south Texas (Hendrix and Show- later stage of a maleÕs life would support frequent ers 1992) into Ames, IA, had very young ovaries (basal mating activity. Although the maleÕs ßight potential ovary width Ͻ0.3 mm: unpublished data). Further- may be less than that of the female at the early stages more, maximum ßight potential in M. separata also of adult life, both males and females are encountered occurs at days 5 and 7 after emergence as determined as immigrants (McNeil 1986, 1987; unpublished data). by tethered-ßight techniques (Zhang and Li 1985, Luo Results of our study and the factor analyses indicate et al. 1995), but the occurrence of migratory ßight for that the choice of ßight parameter used to evaluate this species is much earlier (Chen 1990, Hirai 1991). ßight potential by tethered-ßight techniques could Five-day-old M. separata females that underwent greatly inßuence the conclusions drawn about a spe- 23.5 h of tethered-ßight, however, had lifetime fecun- ciesÕ ßight potential. Factor analyses showed that dities 50and 61% less than females not allowed to ßy Ͻ50% of the variation in longest ßight duration was (control) and females ßown during day-1 of the adult explained by the factor. This variable was not corre- life, respectively (Luo et al. 1999). Similarly, migration lated well with the ßight factor variable. Therefore, if in P. unipuncta moths may be completed earlier than longest ßight duration were used as the sole criterion the occurrence of maximum ßight potential. Also, Þeld of ßight potential in our study, then 10-d-old moths studies have shown that migration of M. separata be- would have been selected as the group with the great- gins one or two days after emergence (Chen 1990, est ßight potential. Furthermore, it would be con- Hirai 1991). Therefore, extrapolating results obtained cluded that the period of maximum migration in P. from tethered-ßight studies to the natural armyworm unipuncta occurs at 10d after emergence, because it population should be done with caution. has generally been assumed that the migratory period P. unipuncta males have a lower ßight potential than corresponds to the period of maximum ßight potential females at early ages, similar to other migratory noc- (Johnson 1969, 1976). Thus, longest ßight duration tuids (Sharp et al. 1975, Parker and Gatehouse 1985, should not be used as the sole parameter to evaluate Sappington and Showers 1991). It is possible that the ßight potential for P. unipuncta. In previous studies, difference in ßight potential was caused by the dif- longest ßight duration was used as the major criterion ferences between the sexes in body weight (Fig. 5) or to evaluate the migratory ßight potential of the black dorsolongitudinal muscle weight. However, the body cutworm (Sappington and Showers 1991, 1992), but it weight of 7- and 10-d-old females was signiÞcantly was only one of several components used to evaluate greater than that of males, whereas there was no dif- ßight potential of Helicoverpa armigera (Hu¨ bner) ference between the sexes within these age classes for (Armes and Cooter 1991). In this study, the other any ßight variable (Figs. 2Ð4). There is evidence that three ßight variables were closely correlated with the in some insects, males may require more energy to ßy ßight factor variable in the factor analyses. However, than females (Rankin and Burchsted 1992, Li and Luo ßight speed might not be a good general indicator of 1999). Greater ßight potential of females before5dof ßight potential because some moths might engage in adult life might be related to females having to carry a short fast ßight without ßying during the remainder the heavy ovary and to seek oviposition sites in addi- of the test. Therefore, high ßight speed may not in- tion to looking for food. In contrast, males only seek dicate great ßight potential unless it is accompanied by food and a mate during this period. It is possible that long ßight duration and vice versa (Luo et al. 1995). the increase in male ßight potential up to 10d of age However, long ßight distance must be indicative of is related to the mating potential of the male. Male P. high ßight potential because it requires relatively fast unipuncta mate up to 11 times, with an average of six or long ßights or both, although the realized migratory (Fitzpatrick and McNeil 1989), and the male must ßight distance in nature is incompletely dependent on 8ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 1 the mothÕs own ßight potential. Based on these anal- biochemistry and pharmacology, vol. 9. Pergamon, Ox- yses, we suggest that at least two ßight parameters ford. should be considered when ßight potential of a highly Dingle, H. 1996. Migration, the biology of life on the move. mobile insect like the true armyworm is assessed by Oxford University Press, New York. tethered-ßight techniques. Flight distance best rep- Fields, P. G., and J. N. McNeil. 1984. The overwintering resented the factor of ßight variables in the factor potential of true armyworm, Pseudaletia unipuncta (Lep- idoptera: Noctuidae), populations in Quebec. Can. En- analyses and either it or total ßight duration should be tomol. 116: 38Ð42. considered as one candidate. Longest ßight duration Fitzpatrick, S. M., and J. N. McNeil. 1989. Lifetime mating should also be considered since it may represent some potential and reproductive success in males of the true additional less-related measure of ßight potential. armyworm, Pseudaletia unipuncta (Haw.) (Lepidoptera: Noctuidae). Funct. Ecol. 3: 37Ð44. Gatehouse, A. G., and X. X. Zhang. 1995. Migratory poten- Acknowledgments tial in insects: variation in an uncertain environment, pp. We thank P. D. Lingren and J. R. Coppedge (Areawide 193Ð245. In V. A. Drake and A. G. Gatehouse (eds.), Insect Pest Management Research Unit, USDA-ARS) for sponsor- migration: tracking resources through space and time. ing, supporting, and providing facilities for this study. This Cambridge University Press, Cambridge. research was funded jointly by USDA-ARS Cooperative Guppy, J. C. 1961. Life history and behavior of the army- Agreement No. 58-6202-5069 with the Areawide Pest Man- worm, Pseudaletia unipuncta (Haw.) (Lepidoptera: Noc- agement Research Unit at College Station, TX, and Louisiana tuidae), in eastern Canada. Can. Entomol. 93: 1141Ð1153. State University Agricultural Center, Baton Rouge, LA. Ap- Guppy, J. C. 1969. Some effects of temperature on the im- proved for publication by the Director, Louisiana Agricul- mature stages of the armyworm, Pseudaletia unipuncta tural Experiment Station as Manuscript number: 00-17-0627. (Lepidoptera: Noctuidae), under controlled conditions. Can. Entomol. 93: 1141Ð1153. Hendrix, W. H., and W. B. Showers. 1992. Tracing black References Cited cutworm and armyworm (Lepidoptera: Noctuidae) northward migration using Pithecellobium and Calliandra Akbulut, S., and M. J. Linit. 1999. Flight performance of pollen. Environ. Entomol. 21: 1092Ð1096. Monochamus carolinensis (Coleoptera: Cerambycidae) with respect to nematode phoresis and beetle character- Hirai, K. 1991. Ascending ßights for migration of the orien- istics. Environ. Entomol. 28: 1014Ð1020. tal armyworm, Pseudaletia separata. Entomol. Exp. Appl. Armes, N. J., and R. S. Cooter. 1991. Effects of age and mated 58: 31Ð36. status on ßight potential of Helicoverpa armigera (Lepi- Johnson, C. G. 1969. Migration and dispersal of insects by doptera: Noctuidae). Physiol. Entomol. 16: 131Ð144. ßight. Methuen, London. Ayre, G. L. 1985. Cold tolerance of Pseudaletia unipuncta Johnson, C. G. 1976. Liability in the ßight system: a context and Peridroma saucia (Lepidoptera: Noctuidae). Can. for functional adaptation. Symp. R. Entomol. Soc. Lond. Entomol. 117: 1056Ð1060. 7: 217Ð234. Beerwinkle, K. R., J. D. Lopez, Jr., D. Chen, P. D. Lingren, Johnson, D. E. 1998. Applied multivariate methods for data and R. W. Meola. 1995. Flight potential of feral Helico- analysis. Brooks/Cole, PaciÞc Grove, CA. verpa zea (Lepidoptera: Noctuidae) males measured with Li, K., and L. Luo. 1999. Activities of enzymes in the ßight a 32-channel, computer-monitored, ßight-mill system. muscle of pupal and adult oriental armyworm moth, My- Environ. Entomol. 24: 1122Ð1130. thimna separata (Walker). Acta Entomol. Sin. 42: 37Ð43. Breeland, C. G. 1958. Biological studies on the armyworm, Luo, L., G. Li, and Y. Hu. 1995. Relationship between ßight Pseudaletia unipuncta (Haworth), in Tennessee (Lepi- capacity and oviposition in the oriental armyworm moth, doptera: Noctuidae). J. Tenn. Acad. Sci. 33: 263Ð347. Mythimna separata (Walker). Acta Entomol. Sin. 38: 284Ð Chapman, P. J., and S. E. Lienk. 1981. Flight periods of 289. adults of cutworms, armyworms, loopers and others Luo, L., X. F. Jiang, K. Li, and Y. Hu. 1999. Inßuences of (Family Noctuidae) injurious to vegetable and Þeld ßight on reproduction and longevity of the oriental crops. Agriculture No. 14. New York State Agricultural armyworm, Mythimna separata (Walker). Acta Entomol. Experiment Station, Geneva, NY. Sin. 42: 150Ð158. Chen, R. 1990. Application of radar in the oriental army- McNeil, J. N. 1986. Calling behavior: can it be used to iden- worm migration research, pp. 293Ð32. In C. S. Lin (ed.), tify migratory species of moths? Fla. Entomol. 69: 79Ð84. Physiology and ecology of the oriental armyworm. Bei- McNeil, J. N. 1987. The true armyworm Pseudaletia jing University Press, Beijing. unipuncta: a victim of the pied piper or a seasonal mi- Cooter, R. J., and N. J. Armes. 1993. Tethered ßight tech- grant? Insect Sci. Applic. 8: 591Ð597. nique for monitoring the ßight performance of Helico- Orchard, I., M. Cusson, and J. N. McNeil. 1991. Adipokinetic verpa armigera (Lepidoptera: Noctuidae). Environ. En- hormone of the armyworm, Pseudaletia unipuncta immu- tomol. 22: 339Ð345. nohistochemistry, amino acid analysis, quantiÞcation and Cusson, M., J. N. McNeil, and S. S. Tobe. 1990. In vitro bioassay. Physiol. Entomol. 16: 439Ð445. biosynthesis of juvenile hormone by corpora allata of Parker, W. E., and A. G. Gatehouse. 1985. The effect of Pseudaletia unipuncta virgin females as a function of age, larval rearing conditions on ßight performance in females environmental conditions, calling behavior and ovarian of the African armyworm, exempta (Walker) development. J. Insect Physiol. 36: 139Ð146. (Lepidoptera: Noctuidae). Bull. Entomol. Res. 75: 35Ð47. Delisle, J., and J. N. McNeil. 1986. The effect of photoperiod Rankin, M. A., and J.C.A. Burchsted. 1992. The cost of mi- on the calling behavior of virgin females of the true gration in insects. Annu. Rev. Entomol. 37: 533Ð559. armyworm, Pseudaletia unipuncta (Haw.) (Lepidoptera: Sappington, T. W., and W. B. Showers. 1991. Implication for Noctuidae). J. Insect Physiol. 32: 199Ð206. migration of age-related variation in ßight behavior of Dingle, H. 1985. Migration, pp. 375Ð415. In G. A. Kerkut and Agrotis ipsilon (Lepidoptera: Noctuidae). Ann. Entomol. L. I. Gilbert [eds.], Comprehensive insect physiology, Soc. Am. 84: 560Ð565. February 2002 LUO ET AL.: FLIGHT POTENTIAL OF P. unipuncta 9

Sappington, T. W., and W. B. Showers. 1992. Reproductive Southwood, T.R.E. 1977. Habitat, the templet for ecological maturity, mating status, and long-duration ßight behavior strategies. J. Anim. Ecol. 46: 337Ð365. of Agrotis ipsilon (Lepidoptera: Noctuidae). Environ. En- Taylor, P. S., and E. J. Shields. 1990. Flight thresholds of the tomol. 21: 677Ð688. armyworm (Lepidoptera: Noctuidae). Environ. Entomol. SAS Institute. 1992. SAS userÕs guides: statistics, 6th ed. SAS 19: 1410Ð1417. Institute, Cary, NC. Turgeon, J. J., and J. N. McNeil. 1983. ModiÞcations in the Saxton, A. M. 1998. A macro for converting mean separation calling behavior of Pseudaletia unipuncta (Lepidoptera: output to letter groupings in PROC Mixed, pp. 1243Ð1246. Noctuidae), induced by temperature conditions during In Proceedings, 23rd SAS UserÕs Group Interational. SAS pupal and adult development. Can. Entomol. 115: 1015Ð Institute, Cary, NC. 1022. Sharp, J. L., J. R. McLaughlin, T. R. Ashley, and D. R. Bennett. Zhang, Z., and G. Li. 1985. A study on the biological char- 1975. Flight ability of Trichoplusia ni in the laboratory. acteristics of the ßight of the oriental armyworm My- Ann. Entomol. Soc. Am. 68: 755Ð758. thimna separata (Walker) moth. Acta Phytophyl. Sin. 12: Shorey, H. H., and R. C. Hale. 1965. Mass rearing of larvae 93Ð99. of nine noctuid species on a simple artiÞcial medium. J. Econ. Entomol. 58: 522Ð524. Southwood, T.R.E. 1962. Migration of terrestrial Received for publication 6 October 2000; accepted 26 Sep- in relation to habitat. Biol. Rev. 37: 171Ð214. tember 2001.