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U.S. Department of Agriculture: Agricultural Publications from USDA-ARS / UNL Faculty Research Service, Lincoln, Nebraska

2002

Beet Armyworm (Lepidoptera: Noctuidae) Host Plant Preferences for Oviposition

S. M. Greenberg Kika de la Garza Subtropical Agricultural Research Center, [email protected]

T. W. Sappington Texas Agricultural Experiment Station

T.-X. Liu Texas Agricultural Experiment Station

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Greenberg, S. M.; Sappington, T. W.; and Liu, T.-X., "Beet Armyworm (Lepidoptera: Noctuidae) Host Plant Preferences for Oviposition" (2002). Publications from USDA-ARS / UNL Faculty. 719. https://digitalcommons.unl.edu/usdaarsfacpub/719

This Article is brought to you for free and open access by the U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Publications from USDA-ARS / UNL Faculty by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. POPULATION ECOLOGY Beet Armyworm (Lepidoptera: Noctuidae) Host Plant Preferences for Oviposition

1 2 2 S. M. GREENBERG, T. W. SAPPINGTON, M. SE´ TAMOU, AND T. -X. LIU

Integrated Farming and Natural Resources Research Unit, Kika de la Garza Subtropical Agricultural Research Center, 2413 East Highway 83, Weslaco, TX 78596

Environ. Entomol. 31(1): 142Ð148 (2002) ABSTRACT Beet armyworm, Spodoptera exigua (Hu¨ bner), oviposition preferences were deter- mined on Þve host plants: cabbage (Brassica oleracea capitata L.), cotton (Gossypium hirsutum L.), bell pepper (Capsicum annuum L.), pigweed (Amaranthus retroflexus L.), and sunßower (Helianthus annuus L.) in no-choice, two-choice, and Þve-choice tests. Tests were conducted in the laboratory, greenhouse, and Þeld cages. Oviposition preferences were compared on the basis of two measure- ments, the proportion of eggs laid on the plants to total that were deposited, and the oviposition preference index deÞned as [(number of eggs laid on the plant) - (number of eggs laid on the cage)] ϫ 100/total number of eggs laid. The proportion of eggs laid on the plants to total that were deposited was highest for pigweed and lowest for cabbage in all tests. Beet armyworm females were signiÞcantly deterred from laying eggs on cabbage and sunßower, while pigweed and cotton elicited a positive oviposition preference. Pepper tended to be neutral or slightly unattractive. Apparent interactions among plant species in choice tests produced measurable shifts in oviposition preference. Most notably, female response to pepper was enhanced in the presence of cotton or pigweed. Egg masses laid on the plants contained signiÞcantly higher numbers of eggs than those laid on the surface of the cage, except in the case of cabbage leaves. Knowledge of hierarchies of host plant oviposition preference by beet armyworm females will be useful in understanding the population dynamics of this important agricultural pest, and for developing effective monitoring and management strategies.

KEY WORDS Spodoptera exigua, beet armyworm, host plants, oviposition preference

THE BEET ARMYWORM, Spodoptera exigua (Hu¨ bner), is a interactions is that of host preference for oviposition, serious pest of numerous wild and cultivated plants but information on this subject with respect to S. throughout the world. It is a cosmopolitan species that exigua is limited. Several studies have addressed S. attacks Ͼ90 plant species in North America, many of exigua oviposition behavior in no-choice situations which are crop plants (Pearson 1982). Insecticides (Mitchell and Heath 1985, Smits et al. 1986, Yoshida directed against the larval stage of beet armyworm are and Parrella 1991, Sappington et al. 2001, Tisdale and the primary method of control, but high tolerance to Sappington 2001), but information is needed regard- most insecticides and associated environmental prob- ing relative preferences when in the presence of mul- lems may jeopardize their continued use (Brewer and tiple potential hosts. Our objectives were to evaluate Trumble 1991, Burris et al. 1994, Sparks et al. 1996, beet armyworm oviposition preferences and egg dep- Mascarenhas et al. 1996, 1998). Therefore, control osition patterns among selected crop and weed spe- programs should not rely solely on insecticides, and cies common to the Lower Rio Grande Valley of Texas. alternative control strategies that prevent the devel- opment of population outbreaks or reduce the cost of Materials and Methods management are needed. Development of effective alternative strategies for Host Plants and Experimental Conditions. Five managing the beet armyworm will require a thorough plant species were used in the study: cabbage (Bras- knowledge of the biological interactions of the insect sica oleracea capitata L.) (Earliana, W. Atlee Burpee, and its hosts. A very important component of such Warminster, PA), cotton (Gossypium hirsutum L.) (DPL-50, Delta Pine Land, Scott, MS), bell pepper This article reports the results of research only. Mention of a (Capsicum annuum L.) (Capistrano, Peto Seed, Sati- commercial or proprietary product does not constitute an endorse- coy, CA), pigweed (Amaranthus retroflexus L.), and ment or a recommendation for its use by USDA. 1E-mail: [email protected]. wild sunßower (Helianthus annuus L.). Pigweed and 2 Texas Agricultural Experiment Station, 2415 East Highway 83, sunßower seeds were collected from local wild plants Weslaco, TX 78596. the previous fall (1999). These plants were selected

0046-225X/02/0142Ð0148$02.00/0 ᭧ 2002 Entomological Society of America February 2002 GREENBERG ET AL.: BEET ARMYWORM OVIPOSITION PREFERENCES 143 based on their importance as cultivated crops (cab- eggs laid on the plants and on the walls of the cage. bage, cotton, and pepper) or their wide distribution as One cage of each plant species was a replication, and weeds (pigweed and wild sunßower) in the Lower Rio there were 16 total replications. Replications were Grande Valley of Texas, as well as their known asso- accumulated two at a time in a series of eight repeated ciations with the beet armyworm. Plants were grown experiments. in 30-cm pots in sunshine mixture #1 (SunGro Hor- Acceptability of intact plants for oviposition were ticulture, Elma, MB, Canada) for laboratory and similarly examined in the greenhouse. Two pots, each greenhouse tests, but were also planted directly in the containing two plants of a given species, were placed soil in Þeld cages. For greenhouse and Þeld tests, we in a screened cage (1 m long by 0.6 m wide by 1 m used intact 30- to 35-d-old plants; in laboratory tests we high). Five 2-d-old mated females were released in used leaves excised from the central canopy of those each cage and allowed to oviposit for 3 d. Four cups, plants. Laboratory and greenhouse experiments were each containing a cotton ball soaked with 10% sucrose, conducted at 26 Ϯ 2ЊC and a photoperiod of 12:12 were placed in each cage for adult feeding. The num- (L:D) h. The greenhouse tests were conducted in ber of egg masses laid on the plants and on the cage January and February and the photophase was length- were recorded daily. One cage containing four plants ened to 12 h by artiÞcial lighting. of a given species was a replication, and there were Insects and Measures of Oviposition Preference. eight total replications. Replications were accumu- Beet armyworm adults were obtained from a labora- lated two at a time in a series of four repeated exper- tory colony maintained at the Kika de la Garza Sub- iments. tropical Agricultural Research Center in Weslaco, TX. Two-Choice Tests. All possible paired combinations They had been reared exclusively on a soybean-wheat of cabbage, cotton, pepper, pigweed, and sunßower germ diet (Shaver and Raulston 1971) for Ϸ3 yr. Spa- were tested, using excised leaves in laboratory and tial placement of egg masses on cotton plants by moths intact plants in greenhouse experiments. In the labo- from this same colony was not grossly different than ratory study, two excised leaves (in ßoral aquapics), that by wild moths (Sappington et al. 2001). We rea- one leaf of each species of a given combination, were soned that the use of uniform insects reared on a placed in a plastic cage. One cage represented one neutral diet would help avoid potentially confounding replication of that combination. Each experiment, effects of dietary history on host plant preference. consisting of one replication of all possible combina- We measured and compared oviposition prefer- tions, was performed at one time, and the experiment ences of the beet armyworm on various host plants was repeated four times. using two different measures. The Þrst measure was In the greenhouse tests, each species of a paired the proportion of the total number of eggs laid that combination was represented by two pots, each con- were deposited on the plant surface. For this measure taining two plants. Thus, each cage contained a total a value Ͼ0.5 was interpreted as an indication the host of four pots. One cage of each possible combination plant was attractive for oviposition. We also used the was a replication. Each experiment consisted of one oviposition preference index of Grant and Langevin replication each of all possible combinations. The ex- (1995): [(number of eggs laid on host plant) Ϫ (num- periment was repeated three times. ber of eggs laid on cage)] ϫ 100/total number of eggs Numbers of beet armyworm females, and methods oviposited. The advantage of the oviposition prefer- of introduction, feeding, and monitoring oviposition ence index over a simple ratio is that it has a Þxed range were as described for the no-choice laboratory and of Ϫ100 to ϩ100, so that a negative value indicates greenhouse tests. Females were allowed to oviposit for oviposition deterrence and a positive value indicates three nights. stimulation. Values not signiÞcantly different from Five-Choice Tests. In these tests moths were ex- zero indicate that the plant is neither repulsive nor posed to all Þve host species simultaneously. Re- attractive for oviposition. sponses to excised leaves were examined in the lab- No-Choice Tests. Acceptability of leaves for ovipo- oratory and responses to intact plants were evaluated sition was examined in the laboratory for each plant in the greenhouse and Þeld cages. In the laboratory species. Leaves were excised near the axil with a razor study, one excised leaf from each of cabbage, cotton, blade and each leaf petiole was immediately placed in pepper, pigweed, and sunßower were held in ßoral a ßoral aquapic with hydroponic solution (Aqua-Ponic aquapics in a cylindrical plastic cage as previously International, Los Angeles, CA). Excised leaves described. Male-female pairs of newly emerged moths rooted readily and did not deteriorate under ßuores- were placed in the cages and females were allowed to cent lighting (20-W, Vita-Lite, Duro-Test Lighting, oviposit for three nights. Provision of food for the ElkGrove, IL) in an incubator. Hydroponic solution adults and the types of data recorded were the same was added to the aquapics as necessary. Two leaves of as described for the laboratory no-choice tests. One a given host plant were placed in a cylindrical plastic cage containing leaves from Þve plant species was a cage (25 cm diameter and 30 cm high) with a nylon- replication, and there were 11 replications in all. screen top. A newly emerged female and male were In the greenhouse, Þve pots each containing two conÞned in each cage for 5 d. Adults were supplied plants of a single species, but with each pot containing with a soaked (10% sucrose) cotton ball in a cup for a different species, were placed in each cage. Five feeding, which was replenished daily. Cages were ex- 2-d-old mated female beet armyworms were intro- amined daily to record the numbers of egg masses and duced to each cage and allowed to oviposit for three 144 ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 1

cal analyses (Sokal and Rohlf 1994). However, results appearing in the text and tables are presented as back- transformed data. The oviposition index of Grant and Langevin (1995) was considered signiÞcantly differ- ent from zero if the 95% conÞdence interval did not span zero. Specimens of beet armyworm were deposited in the insect collection of the Texas Agricultural Experiment Station, Weslaco, TX (voucher # 99Ð05Ð01).

Results No-Choice Tests. In the laboratory tests using ex- cised leaves, the proportion of eggs laid on the plant surface was highest for pigweed (0.612) and lowest for cabbage (0.184) (F ϭ 8.7; df ϭ 4, 75; P ϭ 0.001) (Fig. 1). The only positive response was to pigweed. In the greenhouse tests, we observed a similar trend except that cotton elicited a positive response in addition to pigweed. Overall, the proportions of eggs laid on the plants in the greenhouse were higher than in the laboratory tests, except in the case of sunßower. Mean Ϯ Fig. 1. Mean SE proportions of the total number of proportions of eggs laid on plants in greenhouse tests beet armyworm eggs laid that were deposited on the surfaces followed the hierarchy of pigweed Ͼ cotton Ͼ pep- of excised leaves in a ßoral aquapic (laboratory) or on potted Ͼ Ͼ ϭ ϭ ϭ plants (greenhouse) in no-choice tests. Means accompanied per cabbage sunßower (F 12.7; df 4, 35; P by the same letter within tests (lower case, laboratory; upper 0.038) (Fig. 1). SigniÞcantly negative oviposition pref- case, greenhouse) are not signiÞcantly different (P Ͼ 0.05; erence index values (Grant and Langevin 1995) (Fig. TukeyÕs HSD). 2) indicated that beet armyworm females were de- terred from laying eggs on cabbage, pepper, and sun- ßower in the laboratory and the greenhouse tests. nights. The feeding of adults and data recorded were Two-Choice Tests. The oviposition response of beet the same as described in the greenhouse no-choice armyworm females to the host leaves or plants pre- tests. Each cage (10 plants) was a replication. There were two cages per experiment, and the experiment was repeated two times. Five-choice tests were also conducted in walk-in Þeld cages. Three plots (14.0 m2 each) isolated by screen partitions were divided into Þve randomized rows each three m long, with each row planted to a single host plant species at 10 plants per row. Plots were planted at 10-d intervals. At 30 d after planting, 15 2-d-old females were released in each plot. Plants in the plots were checked for egg masses for 3 d after moths were released. Statistical Analyses. Statistical analyses were con- ducted using analysis of variance (ANOVA) and the independent t-test function of SYSTAT (Zar 1996, SPSS 1998). One-way ANOVA were performed to detect effects of host plant on the two measures of oviposition preference of beet armyworm females. When experiments were repeated, the homogeneity of variance of the individual experiments was tested before pooling data. If there were no differences, the experiments were pooled. When signiÞcant F values were obtained, means were separated using the TukeyÕs honestly signiÞcant difference (HSD) test (no-choice, Þve-choice tests). In the two-choice tests, Fig. 2. Mean Ϯ SE oviposition preference index values means of proportions of the total numbers of eggs laid (Grant and Langevin 1995) for excised leaves in a ßoral that were deposited on the plant surfaces and the aquapic (laboratory) or for potted plants (greenhouse) in oviposition preference indices for each combination no-choice tests. Means accompanied by the same letter were compared with paired t-tests. Proportion data within tests (lower case, laboratory; upper case, greenhouse) were arcsine-square root transformed before statisti- are not signiÞcantly different (P Ͼ 0.05; TukeyÕs HSD). February 2002 GREENBERG ET AL.: BEET ARMYWORM OVIPOSITION PREFERENCES 145

Fig. 4. Mean Ϯ SE proportion of the total number of beet Fig. 3. Mean Ϯ SE proportion of beet armyworm eggs armyworm eggs laid that were deposited on potted plants laid that were deposited on the surfaces of excised host plant when presented with different host-pair combinations in the leaves in ßoral aquapics when presented with different host- greenhouse. Means accompanied by the same letter in paired pair combinations in the laboratory. Means accompanied by combinations are not signiÞcantly different (P Ͼ 0.05; inde- the same letter in paired combinations are not signiÞcantly pendent t-test). different (P Ͼ 0.05; independent t-test). actions among plant types in a pair inßuenced ovipo- sented in paired combinations in the laboratory or sition behavior. greenhouse was consistent with results observed in Five-Choice Tests. When simultaneously presented the no-choice tests (Figs. 3 and 4). Females preferred with all Þve plant species, oviposition preference for to oviposit on pigweed compared with other plants. pepper was similar to that for cotton and pigweed The proportions of the eggs laid by beet armyworm (Fig. 6; Table 1). The respective proportions of total females on cotton plants were signiÞcantly higher eggs laid that were deposited on these three plants than on cabbage and sunßower in both tests (Figs. 3 were not signiÞcantly different, but were signiÞcantly and 4), and on pepper in the laboratory test (Fig. 3). higher than the proportions for cabbage or sunßower Oviposition on pepper was higher than that on cab- in laboratory (F ϭ 11.5; df ϭ 4, 50; P ϭ 0.001) and bage or sunßower. Oviposition on cabbage and sun- greenhouse tests (F ϭ 35.7; df ϭ 4, 15; P ϭ 0.001). ßower did not differ signiÞcantly (P ϭ 0.517). In some In the Þeld-cage tests, the average number of eggs cases, for instance when cabbage was paired with laid per plant on cotton, pigweed, and pepper were not sunßower (laboratory and greenhouse tests, Figs. 3 signiÞcantly different, but were signiÞcantly higher and 4) and when pepper was paired with sunßower than on cabbage or sunßower (Table 1). These results (greenhouse tests, Fig. 4), more eggs were laid on the suggest that the femaleÕs perception of pepper is cage screen than on both plant types combined, fur- changed positively through the interaction of cues ther emphasizing the low acceptability of those host from at least two of the other host plants tested. plants. Egg Mass Size. There were no signiÞcant differences Positive oviposition preference index values indi- in the numbers of eggs per egg mass deposited on cate that pigweed signiÞcantly stimulated oviposition cabbage leaves or on cage walls in either laboratory (Fig. 5). Oviposition preference index values for cot- (t ϭ 0.2, df ϭ 144.8, P ϭ 0.84) or greenhouse exper- ton were consistently positive, but were signiÞcantly iments (t ϭ 0.243, df ϭ 15.9, P ϭ 0.811), or on sun- greater than zero only when paired with pigweed (Fig. ßower leaves compared with those on cage walls in the 5). In contrast, oviposition preference index values for laboratory tests (t ϭ 0.804, df ϭ 170.0, P ϭ 0.422). In cabbage and sunßower were signiÞcantly negative in all other cases, the sizes of egg masses were signiÞ- all cases. Response to pepper was signiÞcantly re- cantly higher on the plants than on cage walls (Table duced when it was paired with cabbage or sunßower 2). Egg mass size was signiÞcantly greater on pigweed (Fig. 5). Also, cotton was more attractive for ovipo- and cotton than on pepper and sunßower in the lab- sition when it was presented with pigweed than when oratory tests (F ϭ 5.9; df ϭ 4, 379; P ϭ 0.001), and it was presented with cabbage (Fig. 5). Thus, inter- signiÞcantly greater than on cabbage, pepper, and 146 ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 1

Fig. 6. Mean Ϯ SE proportions of the total number of beet armyworm eggs laid that were deposited on excised leaves of Þve different host plants in ßoral aquapics and Fig. 5. Mean Ϯ SE oviposition preference index values presented simultaneously or on potted plants of Þve different (Grant and Langevin 1995) of beet armyworm for potted hosts presented simultaneously. Means accompanied by the plants when presented with different host-pair combinations same letter within tests (lower case, laboratory; upper case, in the greenhouse. Means accompanied by the same letter in greenhouse) are not signiÞcantly different (P Ͼ 0.05; TukeyÕs paired combinations are not signiÞcantly different (P Ͼ 0.05; HSD). independent t-test). ßower and cabbage combined made pepper more at- ϭ ϭ sunßower in the greenhouse tests (F 14.7; df 4, 50; tractive, but this seems unlikely given the apparent ϭ P 0.002) (Table 2). lackof such a negative effect on pepperÕs oviposition preference index values in the pairwise greenhouse Discussion trials compared with its oviposition preference index value in isolation. The beet armywormÕs polyphagous nature has been The nature of the host plant cues recognized by interpreted as evidence that the moth oviposits indis- beet armyworm females is unknown, but could be criminately on any available plant species (Atkins chemical, tactile, visual, or some combination. Differ- 1960), but our results clearly show that oviposition ences in oviposition response to isolated leaves com- preferences existed among the Þve host plants tested. pared with whole plants suggest that tactile cues Even when given no choice of host plant, females (which should be the same in either experiment) are tended to lay more eggs on the cage screen than on less important than chemical or visual cues in the case cabbage or sunßower suggesting that cues from these of cotton, pigweed, and sunßower, but this may not be plants were not simply nonstimulating, but were less the case with cabbage. Dependence of differential attractive than the wire screen. In contrast, pigweed changes in oviposition behavior toward a given host on and to a lesser extent cotton in potted plant experi- the species of a nearby host suggests that chemical ments were signiÞcantly attractive for beet armyworm cues maybe more important than tactile cues, and oviposition. Pepper tended to be neutral or slightly less attractive than the cage. Table 1. Mean ؎ SE numbers of egg masses and eggs oviposited In general, the hierarchy of preference suggested by on selected host plants exposed to beet armyworm females in a field the no-choice tests was reßected in the results of the cage five-choice test two-choice and Þve-choice tests. The highest propor- tion of total eggs laid were on pigweed, followed by Host plant n Egg masses per plant Eggs per plant cotton and pepper. Sunßower and cabbage were Cabbage 60 0.92 Ϯ 0.46b 29.6 Ϯ 13.6b clearly less attractive. However, it is clear that ovipo- Cotton 60 1.45 Ϯ 0.16ab 156.8 Ϯ 36.8a sition preference and behavior are somewhat context- Pepper 60 1.26 Ϯ 0.33ab 121.8 Ϯ 29.8a Ϯ Ϯ dependent. The femaleÕs perception of pepper in an Pigweed 60 1.8 0.46a 147.5 30.5a Sunßower 60 0.33 Ϯ 0.33c 8.3 Ϯ 7.1b isolated context is changed positively through the in- teraction of cues from either cotton or pigweed, or Means within a column and followed by the same letter are not both. It is possible that negative cues from both sun- signiÞcantly different (TukeyÕs HSD, P Ͼ 0.05). n, number of plants. February 2002 GREENBERG ET AL.: BEET ARMYWORM OVIPOSITION PREFERENCES 147

Table 2. Mean ؎ SE numbers of beet armyworm eggs per egg mass on respective plant and cage surfaces for selected host plants in no-choice tests

Mean Ϯ SE no. of eggs per egg mass Host Laboratory tests (on excised leaves) Greenhouse tests (on intact plants)

Leaves (n) Cage Plants (n1) Cage Cabbage 54.0 Ϯ 4.0abA (74) 53.3 Ϯ 4.5aA 28.9 Ϯ 3.5cA (13) 28.9 Ϯ 1.4bA Cotton 68.2 Ϯ 4.7aA (100) 39.7 Ϯ 3.0bB 96.4 Ϯ 9.3aA (10) 53.4 Ϯ 1.9aB Pepper 46.6 Ϯ 4.1bA (50) 26.6 Ϯ 2.4bB 66.2 Ϯ 7.2bA (12) 49.5 Ϯ 1.8aB Pigweed 66.6 Ϯ 4.3aA (90) 48.6 Ϯ 4.7abB 86.3 Ϯ 11.9aA (10) 50.6 Ϯ 2.6aB Sunßower 46.0 Ϯ 3.5bA (70) 41.5 Ϯ 4.3abA 37.7 Ϯ 3.9bcA (10) 25.2 Ϯ 2.0bB

Means within a column followed by the same lower case letter are not signiÞcantly different (TukeyÕs HSD, P Ͼ 0.05). Pairs of means within Ͼ a row (by test) followed by the same upper case letter are not signiÞcantly different (t-test. P 0.05). n - number of leaves, n1 - number of plants. perhaps more important than visual cues, in host plant The size of egg masses deposited on the cage screen discrimination by females. However, experiments de- in our tests reßected the size of egg masses deposited signed to speciÞcally test these hypotheses will be on the corresponding potted host plant in that cage. necessary to dissect the relative importance of poten- This is consistent with volatile chemical cues being tial cues inßuencing oviposition preference in these important in beet armyworm host-dependent ovipo- different contexts. sition behavior. However, the hierarchical pattern of Interestingly, host plant choice is not the only be- size of egg masses oviposited on the screen did not havioral adaptation of females related to placing off- correspond to that on the isolated leaves. The hierar- spring on suitable host plants. The average number of chy of egg mass size on isolated leaves followed a eggs per egg mass depended on the host plant, and similar pattern as that on potted plants, but the dif- followed the same hierarchical ordering as host plant ferences were of lesser magnitude. preference. The difference between egg mass size on Knowledge of hierarchies of host plant oviposition potted cabbage and that on potted cotton or pigweed preference by beet armyworm females will be useful was 2.5- to 3-fold. In parallel studies, we found that in designing cultural management strategies, which indices of beet armyworm developmental efÞciency may include trap cropping. Wild and cultivated plant from larva to adult depended on host plant, also in the hosts of beet armyworm serve as important reservoirs same hierarchical order. For example, development for populations that subsequently infest other crops. on pigweed from Þrst instar to pupa was several days Successful management of these populations, and es- faster, and required less gram-intake of leaf tissue than pecially avoidance of severe outbreaks, will require a development on cabbage (Greenberg et al. 2001). more complete understanding of beet armyworm Thus, it appears that the host plant oviposition pref- ecology in the diverse ecological system within which erence hierarchy of beet armyworm females corre- crops are grown. sponds to nutritive value of the potential hosts, and that egg mass size can be modiÞed to reßect the per- Acknowledgments ceived suitability of a host that a female has selected for oviposition. Host-dependent variation of egg mass We acknowledge the technical assistance of J. Caballero, size or clutch size has been reported in other insects P. Carreon, and L. Leal. We thankMartin Avila (USDA, ARS, (Van Leerdam et al. 1984, Grant and Langevin 1995). KdlG SARC, BeneÞcial Insect Research Unit, Weslaco, TX) Sappington et al. (2001) reported 29% fewer eggs per for assistance in beet armyworm rearing. We are grateful to D. W. Spurgeon and J. Lopez (Areawide Pest Management egg mass oviposited by beet armyworm on cotton Research Unit, Southern Plains Area USDA-ARS, College compared with that on pigweed in Þeld cage tests, Station, TX) for critical reviews of the manuscript. whereas the results reported herein revealed no dif- ferences between these two hosts in isolated leaf and potted-plant experiments. In greenhouse studies, References Cited Smits et al. (1986) found that variation in beet army- Atkins, E. L., Jr. 1960. The beet armyworm, Spodoptera ex- worm egg mass size did not vary among hosts that igua, an economic pest of citrus in California. J. Econ. included chrysanthemum, tomato, gerbera, and gera- Entomol. 53: 616Ð619. nium, but that younger chrysanthemums received Brewer, M. J., and J. T. Trumble. 1991. Inheritance and more eggs than older plants. In our study, plant age Þtness consequences of resistance to fenvalerate in Spo- was uniform, but plant development may not be equiv- doptera exigua (Lepidoptera: Noctuidae). J. Econ. Ento- alent across the species we tested at the chosen age. mol. 84: 1638- 1644. Burris, E., J. B. Graves, B. R. Leonard, and C. A. White. 1994. An important variable yet to be studied is the effect of Beet armyworms (Lepidoptera: Noctuidae) in northeast plant age and phenology on host plant preference and Louisiana: observations on an uncommon insect pest. Fla. oviposition behavior. For example, physiologically Entomol. 77: 454Ð459. young cotton may be more or less attractive than Grant, G. G., and D. Langevin. 1995. Oviposition deter- nearby physiologically old pigweed. rence, stimulation, and effect of clutch size of Choristo- 148 ENVIRONMENTAL ENTOMOLOGY Vol. 31, no. 1

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