Journal of the Kansas Entomological Society · 1997 · 14 citations · 0 references
Life SciencesEcologyEntomologyInsect EcologyInsect SystematicsInvertebrate ZoologyAquatic Insect EcologyInsect Life History EcologyLarval SurvivalLife TablesMortality ProfilesParasitoid BiologyDemographic Life TablesEgg MortalityLarval Survival AnalysisLarval Survival EstimationLife History ComparisonsPredation On LarvaeSurvival Across Life StagesSurvival Rate Estimation
Eggs, larvae, and adults of the introduced Palearctic species Coccinella septem punctata L. and the indigenous Coleomegilla maculata (Degeer) were sampled in spring al falfa along with their prey, Acyrthosiphon (Harris) (Homoptera: Aphididae), to deter mine their temporal occurrence, rate of survival, and density of A. pisum. A partial life table was constructed for the first, second, and third of both coccinellid species. The larvae and adults of both predators overlap spatially and temporally in spring alfalfa, and mortality from first instar through third instar was high for both species (93.0% for C. maculata and 90.8% for C septempunctata). Adult density ranged from 7.0 to 11.8 adults per m2 for C. maculata and from 5.9 to 11.8 adults per m2 for C. septempunctata. The density of A. ranged from 5.4 to 116.7 aphids per m2. Coccinella septempunctata L. (Cole?ptera: Coccinellidae) is a Palearctic aphid ophagous coccinellid that has established and spread rapidly throughout the United States (Angalet et al., 1979; Cartwright et al., 1979; Schaefer et al., 1987). In South Dakota densities of two coccinellid species, Adalia bipunctata and Coccinella trans versoguttata, were reduced following the establishment of C septempunctata (El liott et al., 1996). This predatory species is commonly found in herbaceous vegeta tion (e.g., alfalfa) along with several indigenous coccinellid species, such as Coleomegilla maculata (Degeer) (Cole?ptera: Coccinellidae) (Obrycki et al., 1987; Giles et al., 1994; Elliott et al., 1996). In alfalfa these predators often feed on the pea aphid, Acyrthosiphon (Harris) (Homoptera: Aphididae), which is a suitable prey for the development of both C. septempunctata and C. maculata (Smith, 1965; Hodek and Honek, 1996; Obrycki and Orr, 1990; Ormord, 1994). Previously, Kirby and Ehler (1977) analyzed egg to adult survival of Hippodamia convergens Guerin (Cole?ptera: Coccinellidae) feeding on Rhopalosiphum maidis (Fitch) and Schizaphis graminum (Rondani) (Homoptera: Aphididae) in sorghum. Generation mortality of//, convergens ranged from 93.1 to 99.9%, with highest mor tality occurring in the egg stage and in small larvae (first and second instars) (Kirby and Ehler, 1977). The objectives of this research were to document the presence of eggs and larvae of both C. maculata and C. septempunctata in spring alfalfa in relation to the den sity of their prey, A. pisum, and to measure the survival rate of eggs, larvae, and pu pae of these two coccinellid species. Accepted for publication 14 January 1998. 1 2121 Walnut Street, Cedar Falls, Iowa 50613. 2Kristopher L. Giles, Oklahoma State University, 127 Noble Research Center, Stillwater, Oklahoma 97331. Address for correspondence: John J. Obrycki, Iowa State University, Department of Entomology, Ames, Iowa 50011-3140. PH: 515-294-8622; FAX: 515-294-8027; E-mail: jobrycki@iastate.edu This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 06:30:46 UTC All use subject to http://about.jstor.org/terms 340 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY Materials and Methods One alfalfa field (approximately 4000 m2) located in Ankeny, Polk County, Iowa was sampled every three to five days from 5 May to 11 June in 1992 for a total of 12 sampling days. The field was divided into four equal-sized plots (15mxl5m = 225 m2); each plot was separated by 15 m. Two types of samples were taken on each sampling day in each of the four plots. Samples of cut foliage were used to estimate coccinellid egg and pupal densities. A sampling unit consisted of randomly tossing a 0.093-m2 sampling frame and cutting all of the vegetation at ground level in half of the area (0.046 m2). The cut foliage was placed in a plastic bag, chilled, and returned to the laboratory, where coccinellid eggs and pupae were counted and collected. The remaining debris on the ground in the sampled area was also searched, in situ, for coccinellid eggs and pupae, which were collected and counted. Ten foliage samples were taken in each plot on each sampling day (total of 40 for the whole field). The second sampling method used was suction sampling which consisted of ran domly tossing a 0.093-m2 sampling frame and the use of a gasoline-powered leaf blower with a vacuum attachment. Using this method all insects in an area of 0.093 m2 were removed. Insects were captured in a fine mesh net, which was inserted over the end of the vacuum tube before they could enter the machine. Captured insects and debris were placed in plastic bags, chilled, and returned to the laboratory, where coccinellid larvae and adults, and pea aphids (A. pisum) were counted. Five samples were taken in each plot on each sampling day (total of 20 for the whole field). Coccinellid eggs that were collected were held at 22?C ? 1?C/16:8 (L:D) until lar vae eclosed. All larvae that were collected in the field were reared on a diet of A. at 22?C ? 1?C/16:8 (L:D) until they reached the adult stage. Dates of eclosi?n were noted so that the larval stadium at the time of collection could be accurately determined. Pupae collected in the field were held at 22?C ? 1?C/16:8 (L:D) until adults emerged. Partial life tables were constructed for C. maculata and C. septempunctata fol lowing methods described by Southwood (1978). Mortality estimates were made for the first, second, and third of each species because fourth and pupae were still being collected when the alfalfa was cut on 12 June. We estimated the to tal number of fourth because this stage had almost been completed when the alfalfa was cut. This estimation was done by determining the expected date when the last fourth of each species would be present based on the last date that third were present and the degree day accumulation required to complete the fourth larval stadium. Parameters estimated in the partial life table analysis were: lx?the number of in dividuals entering stage x; dx?the number of individuals dying in stage x; lOOqx? the percent mortality in stage x; and lOOSx?the percent surviving stage x (South wood, 1978). The number entering a stage was calculated by integrating the density estimates for each stage over accumulated degree days for that stage, then dividing by the degree days required for development of the stage (Southwood, 1978). The degree day requirements for development of each C. maculata life stage were from Obrycki and Tauber (1978) and for C. septempunctata from Obrycki and Tauber (1981). Voucher specimens of C. maculata, C. septempunctata, and A. are deposited This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 06:30:46 UTC All use subject to http://about.jstor.org/terms VOLUME 70, ISSUE 4 341 Table 1. Mean number of A. per m2 (?SE) on each sampling day, prior to alfalfa being cut on 12 June 1992. Month Day Mean A. pisum SE May 05 20.43 4.4065 May 08 31.18 5.1688 May 13 26.88 5.0258 May 16 60.75 8.5548 May 19 77.96 9.3570 May 22 116.67 14.0903 May 26 102.69 10.1548 May 29 55.91 7.6269 June 01 21.51 3.2161 June 04 8.06 2.1892 June 08 9.14 2.2441 June 11 5.38 1.6548 a Mean based on four plots with five suction samples in each plot. in the Iowa State University Insect Collection, Department of Entomology, Iowa State University, Ames, Iowa 50011, USA. Results and Discussion Densities of A. ranged from 5.4 to 116.7 aphids per m2 during the sampling period from 5 May to 11 June, with a peak in density occurring in the middle of the sampling period (22 May) (Table 1). The decline in aphid density coincides with the appearance of third and fourth instar C. maculata and C. septempunctata (Tables 1-3). The area searched by coccinellid larvae in the field is not well understood. Newly eclosed unfed first can travel over 0.50 m in search of their first meal (Boldyrev and Wilde, 1969). We have shown in a laboratory study that one large pea aphid per day is sufficient for C. maculata and C. septempunctata larvae to complete development to the adult stage. Survival increases from 63 to 78.9% for C. macu lata and from 33 to 83% for C. septempunctata when prey is doubled to two pea aphids per day (Ormord, 1994). Therefore, it would appear that sufficient prey was available in this alfalfa field for both species to complete their development. Egg mortality could not be estimated because the egg sampling method underes timated the number of eggs that were actually present (based on the number of sam pled first instars). Fewer eggs of C. maculata were sampled than first (Table 4). Even though more eggs of C. septempunctata were sampled than were first in stars, we assumed that the technique still underestimated egg numbers based on our experience with C. maculata (Table 5). All C maculata and C septempunctata egg masses were found either on the de bris after the foliage had been cut and removed or on the soil surface. No egg masses were found on the living foliage that was cut and removed from the plot. Eggs masses may have been missed when the debris was examined in situ. Eggs of coc cinellids are usually assumed to be deposited near a source of prey for the larvae (Hodek and Honek, 1996). In short, herbaceous vegetation such as alfalfa, eggs de posited on soil surface debris would be close to aphid prey in the plant canopy. This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 06:30:46 UTC All use subject to http://about.jstor.org/terms 342 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY Table 2. Mean number of C. maculata eggs, first instars, second instars, third instars, fourth instars, pupae, and adults per m2 (?SE) on each sampling date in 1992 before the alfalfa was cut on 12 June. Month Day Eggs' First instarsb Second instars Third instarsh Fourth instars Pupaea Adults