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Kaytora Long Journal of Undergraduate Research Volume 8, Issue 1 - September / October 2006 Evaluation of Various Mediums for Rearing Bigeyed Bugs Geocoris punctipes (Say) a Beneficial Predator for Controlling Insect Pest Populations Kaytora Long ABSTRACT The bigeyed bug, Geocoris punctipes (Say), is an important beneficial predator in many agricultural systems. It feeds on many stages of insect pests. Three types of mediums were evaluated on Geocoris punctipes to determine which medium will best promote ovipostion (egg laying) and the development of G. punctipes to nymphs and adults. The three mediums evaluated were cotton balls, cotton squares, and polyester/rayon gauze. The experimental design was completely randomized with four replicates per treatment (medium). The results indicate that cotton balls produced the highest number of eggs, nymphs, and adults. This can serve as a rearing material in which G. punctipes will successfully reproduce and develop; therefore, facilitating the rearing of G. punctipes under laboratory conditions. INTRODUCTION Bigeyed bugs, Geocoris spp., are commonly used for biological control of key agricultural pests in Integrated Pest Management (IPM) programs in the United States. There are several species of Geocoris; however, one of the most common species is G. punctipes (Say). Geocoris spp. feed on all life stages of whiteflies, mites, and aphids (Hagler 2006) and are used for their predatory status on eggs and small larvae of lepidopteran pests. Several studies indicate that G. punctipes are effective predators of insect pests in many agricultural systems (Dumas et al. 1962, McCutcheon & Durant 1999). Geocoris spp. can be produced in large quantities under laboratory conditions, yet information pertaining to their choice of reproductive mediums is unavailable. The ultimate goal of this project was to identify a rearing medium in which bigeyed bugs can successfully reproduce. Therefore, the specific objective of the study was to identify the reproductive medium that will promote the development of G. punctipes eggs and nymphs. This project compared the number of G. punctipes eggs deposited on either cotton balls, cotton squares, or polyester/rayon gauze, and determined which medium best supports egg production; as well as the survival of nymphal bigeyed bugs into adulthood. MATERIALS AND METHODS Geocoris punctipes adults used for this study were taken from a colony maintained in the Fruit and Vegetable Laboratory at the University of Florida, Gainesville, and reared in ventilated containers. Various sizes of containers were used to maintain separation of bigeyed bug adults, newly emerged nymphs, and mediums. Adult containers were 37 x 25 cm in size, nymphal containers were 20 x 20 cm, and newly emerged/ medium containers were 13 x 13 cm. Colonies were maintained by adding water in the form of water soaked-cotton wicks, green beans, and Ephestia kuehniella Keller eggs as a food source. All containers had shredded wax paper to serve as hiding places for both adults and nymphs. Each adult container had cotton balls, cotton squares, or polyester/rayon gauze provided as ovipositional substrates for the randomly selected 120 adult bigeyed bugs. Cotton balls used in this study were 6.48 cm3 (Wal-Mart, Mentor, OH) [Fig. 1a]. Cotton squares were old-fashioned “diaper cloth” cut into 9.50 x 6.50 cm semi-squares (Gerber Products Company, Fremont, Michigan) [Fig. 1b]. Polyester/ Rayon gauze, used to wrap wounds, was cut into 10.0 x 7.0 cm rectangles (Johnson & Johnson, New Brunswick, NJ.) [Fig. 1c]. Figure 1. Shows the mediums used for the study. Fig. 1a shows the cotton ball medium. Fig. 1b shows the cotton square medium. Fig. 1c shows the polyester/rayon medium. A total of six cotton balls were placed into each adult container and arranged into two bundles, with each bundle on opposite sides of the adult container. For the second treatment, a total of two gauze squares were placed on opposite sides of an adult container, and in the third treatment two cotton squares were placed on opposite sides of an adult container. The experiment was replicated four times per treatment in a completely randomized design. Containers that contained the various treatments (cotton balls, cotton squares, polyester/rayon gauze) were kept in and environmental chamber at 22.2 °C with 65.3% RH with 14:10 light:dark period, respectively. Cotton balls, cotton squares, and polyester/rayon gauze were removed from Environmental Chamber 1 every seven days. Once the mediums were collected bigeyed bug eggs were counted, and placed into the 13 x 13 cm containers that corresponded to the date the substrates were counted. Water-soaked cotton wicks, green beans, and Ephestia kuehniella Keller eggs were provided as food sources in the new containers. The mediums were maintained in ventilated containers for a period of 14 days. Each medium was sprayed with 1ml of deionized water every two days to maintain moisture. The length of time eggs took to hatch was three to four days. Upon the end of the incubation period, newly emerged bigeyed bugs were counted and nymphs were separated into containers according to the type of medium in which they emerged. This process was repeated each week for a total of 14 days. Nymphs taken from the initial seven day counts were transferred into larger, 20 x 20 ventilated containers and incubated in a second environmental chamber at an average of 22.2 °C and 65.3% RH. Nymphal food sources remained the same as adults. Seven days later these insects were recounted to determine if they survived for at least 14 days from their initial emergence. Therefore, the surviving nymphs were assumed to reach adulthood. RESULTS & DISCUSSION Eggs Throughout the period of evaluation, G. punctipes laid significantly more eggs on cotton balls than on cotton squares or polyester/rayon gauze (Fig. 2). The mean number of eggs laid on cotton balls in June, July, and August was 854.6 ± 124.0, 720.8 ± 103.2, and 619.4 ± 71, respectively. In September, eggs laid on cotton balls dropped significantly to 363.8 ± 57.7 and the decline continued until November (243.8 ± 42.0) when the study was completed (Fig. 2). The reason for this decline was unclear; however, a study conducted by Ruberson, et al. (2001) found that there are no notable developmental effects of photoperiods in embryonic or nymphal stages when kept at 14:10 light:dark period. Figure 2. Eggs laid by bigeyed bugs in various mediums (June - November) *Bars followed by the same letter are not significantly different using LSD mean separation α = 0.05 In this study, cotton balls, cotton squares, and polyester/rayon gauze were incubated at an average of 22.2 °C and 65.3% RH. The environmental chamber was maintained at a 14:10 (LD) photoperiod, which is ideal for bigeyed bug reproduction. Therefore, fecundity on the mediums studied was not affected by the photoperiod or temperature. The results of the cotton squares and the polyester/rayon gauze did not show a significant difference in the amount of eggs laid except for the mouth of August. The number of eggs laid on the cotton squares and the polyester/rayon gauze was generally low. The highest number of eggs laid on cotton squares was in June at 210.0 ± 79.1, and the highest number of eggs laid on the polyester/rayon gauze was also in June at 140.2 ± 37.80 (Fig. 2). Overall, there was a significant difference among all treatments cotton balls (529.9 ± 55.8), cotton squares (141.5 ± 18.2), and polyester/rayon gauze (91.4 ± 11.2) (F = 38.89; df = 2, 70; P < 0.0001). Nymphs Significantly more nymphs emerged from eggs laid on the cotton balls throughout the entire observation period except in August when there was no significant difference between cotton squares and polyester/rayon gauze (F = 31.64; df = 2, 165; P < 0.001) (Fig 3). Overall, approximately five times as many nymphs were produced on cotton balls compared with the other mediums evaluated. There were no significant differences among the number of eggs laid on cotton squares and polyester/rayon gauze throughout the observational period (Fig. 3). Figure 3. Nymphs emerged from various mediums (June - November) *Bars followed by the same letter are not significantly different using LSD mean separation α=0.05. Adults More than 70% of nymphs reared from cotton balls made it to the adult stage. The percentage of adults that resulted from cotton squares and polyester/rayon gauze was significantly less than cotton balls. CONCLUSION Although G. punctipes are widely known predaceous species, reproductive habits are unknown. This study has shown that the bigeyed bug’s artificial medium of choice is cotton balls. Their preference may be due to the female’s natural instinctive ability to protect her eggs from natural enemies. My observation of the cotton balls noted that the eggs were deposited deep into the substrate where they cannot be eaten by other predators. In this experiment cannibalism of the bigeyed bugs was observed. Predation of their own eggs was not recorded, although empty chorions appeared in all three mediums. Cohen (1985) indicated that adult and nymphal G. punctipes are frequently observed probing eggs of their own species even when they are provided with natural diets. The use of cotton balls as an ovipositional substrate will facilitate the rearing of G. punctipes under laboratory conditions. The difference in the number of eggs laid on cotton balls compared with the cotton squares and polyester/rayon gauze can be attributed to the structure of the material. The structure of the cotton ball is less dense than either the cotton squares or the polyester/rayon gauze. The cotton fiber is loosely woven into a more open, “fluffy” ball, in contrast to the tightly woven material of woven cotton fibers and polyester/rayon gauze.
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