University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln 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 Follow this and additional works at: https://digitalcommons.unl.edu/usdaarsfacpub Part of the Agricultural Science Commons 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.