Showing papers in "Journal of the Kansas Entomological Society in 1992"

Numerical responses of aphid predators to varying prey density among Utah alfalfa fields

Abstract: Insect natural enemies are often hypothesized to exhibit spatial as well as temporal density dependence in responding to their prey. To evaluate the potential im portance of spatial density dependence in biological control of pea aphids (Acyrthosiphon pisum) in Utah alfalfa, we examined whether the distributions of aphid predators varied in relation to densities of their prey among fields. Sweep samples were taken for predators and prey during five periods over the growing season in fields scattered throughout a five km2 area. Densities of generalist predatory insects, damselbugs (Nabidae) and big-eyed bugs (Lygaeidae: Geocorinae), were not correlated with prey density on any occasion. In contrast, densities of the more narrowly aphidophagous ladybeetles (Coccinellidae) were strongly positively correlated with aphid densities among fields early (but not late) during the growing season. Alfalfa weevils (Hypera postica) were numerous at the study sites, and served as alternate prey for aphid predators. With the exception of damselbugs in early May, however, densities of ladybeetles, big-eyed bugs, and damselbugs were not correlated with alfalfa weevil densities among fields throughout the growing season. Differences in diet breadth best explain the contrast between the positive numerical response of specialist ladybeetles to spatial variation in aphid density, and the absence of such responses by generalist insect predators. Abundant evidence suggests that natural enemies often play major roles in the population dynamics of phytophagous insects (e.g., Strong et al., 1984; Luck et al., 1988). Of key interest are the degree to which these enemies (1) depress (determine) host population density, and (2) stabilize (regulate) long-term fluc tuations of host density (Hassell and Waage, 1984). Successful regulation of hosts at low densities has been conventionally the ultimate goal of biological control (Murdoch et al., 1985). Such regulation, furthermore, has generally been hypoth esized to depend on direct density dependent responses of natural enemies to their hosts, such that the intensity of natural enemy attack (e.g., percent parasitism) rises with increasing host density (Huffaker et al., 1976; Batra, 1982; Stiling, 1987). In addition to temporal density dependence, spatial density dependence has been widely considered to contribute instrumentally to successful biological con trol (see discussions in Readshaw, 1973; Hassell and Waage, 1984; Hassell, 1985; Walde and Murdoch, 1988). The potential importance of direct spatial density dependence in predator/prey interactions is highlighted by a diversity of math ematical models (e.g., Hassell and May, 1973, 1974; Beddington et al., 1978; Hassell, 1985,1987;KareivaandOdell, 1987; Walde and Murdoch, 1988). Recent summary reviews, however, indicate that such direct spatial density dependence occurs relatively infrequently (and about as frequently as inverse density depen dence) in host/parasitoid interactions in the field (Morrison and Strong, 1980; Lessells, 1985; Stiling, 1987; Walde and Murdoch, 1988). These findings call into Accepted for publication 10 September 1991. This content downloaded from 207.46.13.51 on Sun, 19 Jun 2016 06:18:54 UTC All use subject to http://about.jstor.org/terms VOLUME 65, NUMBER 1 31 question the general importance of spatial density dependence in insect biological control (Smith and Maelzer, 1986; see also Pacala et al., 1990). Spatial patterns in insect predator/prey (vs. parasitoid/host) interactions have been relatively little studied (but see Readshaw, 1973; Hull et al., 1976; Nachman, 1981; Kareiva, 1984, 1985, 1987; Riechert and Lockley, 1984; Nyrop, 1988; Turchin and Kareiva, 1989). The present study examines whether aphid predators exhibit a numerical response to spatial variation in the density of their prey among alfalfa fields. As adults, many of these predators are highly mobile insects with the potential to seek out and exploit large concentrations of prey over space and time (e.g., Hagen, 1962; Ewert and Chiang, 1966; Kieckhefer and Olson, 1974; Neuenschwander et al., 1975). Experimental evidence suggests that these predators are often instrumental in keeping aphid densities low in alfalfa and other crops (Way and Banks, 1968; Frazer et al., 1981; Kring et al., 1985; Rice and Wilde, 1988). Furthermore, at least some of these predators show strong positive nu merical responses over time to changing aphid densities (Neuenschwander et al., 1975; Wright and Laing, 1980). Frazer et al. (1981) suggested that spatial density dependence is exhibited by aphid predators (ladybeetles) within alfalfa fields, as these predators aggregate and thereby prevent aphid populations from increasing rapidly. In a series of inno vative field experiments, Kareiva (1984, 1985, 1987) demonstrated that habitat fragmentation disrupted the capacity of ladybeetles to aggregate, allowing local aphid populations within goldenrod fields to outbreak. Because it is important to understand how the degree of density dependence varies with spatial scale (Mor rison and Strong, 1980; Heads and Lawton, 1983), we have focused on an es pecially large spatial scale here by examining how the distributions of aphid predators vary in relation to aphid density among individual alfalfa fields.

Female size and nest defense in the digger wasp Cerceris fumipennis (Hymenoptera: Sphecidae: Philanthinae).

Abstract: An aggregation of the philanthine wasp Cerceris fumipennis Say was observed during nest-founding from March 25-31, 1989, at the Archbold Biological Station, Florida. Newly emerged wasps were individually marked and measured for head width. Observa tions of 35 nests over six daily activity periods revealed frequent nest switching and nest usurpation. Larger females displaced smaller females from their nests, and larger females maintained residence longer than smaller females. As a consequence, the average size of females holding a nest increased significantly during the nest-founding phase, but the average size of all females observed at the nest aggregation did not change during the same period. Size therefore predicts a female wasp's likelihood of acquiring and retaining a nest, suggesting that large females are competitively superior to small females during nest founding. In some cases, two females appeared to share a nest, but did not provision

Life history and development of Scymnus frontalis (Fabricius) (Coleoptera: Coccinellidae) on four species of aphid

Abstract: The ladybird beetle, Scymnus frontalis (Fabricius), was imported from Tur key as a potential predator of the Russian wheat aphid, Diuraphis noxia (Mordviklo). Larval developmental time and adult fecundity were examined for S. frontalis fed four aphid species: the Russian wheat aphid; the greenbug, Schizaphis graminum (Rondani); the English grain aphid, Macrosiphum avenae (L.); and the pea aphid, Acyrthosiphon pisum (Harris). Larvae reared on Russian wheat aphids completed development 0.7 to 1.4 days sooner and weighed 0.5 to 0.3 mg less than those reared on English grain aphids or pea aphids, respectively. No differences were found in adult survival or fecundity for adults reared on Russian wheat aphids, greenbugs, or pea aphids. The intrinsic rate of increase (0.73) was significantly greater for S. frontalis fed Russian wheat aphids compared with those fed pea aphids or greenbugs (0.60 and 0.63, respectively). In a prey preference test, S. frontalis larvae ate 323/600 firstor second-instar Russian wheat aphids and 274/600 English grain aphids indicating a slight preference for Russian wheat aphids as prey. The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), has become a threat to wheat production in the United States since its introduction in 1986 (Thompson, 1987; Stoetzal, 1987). The RWA is believed to be indigenous to the southern Soviet Union, Iran, Afghanistan and countries which border on the Mediterranean, where it is not considered a serious pest. Introduction of natural enemies from these areas to the United States may facilitate biological control of the RWA. One potential natural enemy of the RWA which was imported from Turkey into the United States is the ladybird beetle, Scymnus frontalis (Fabricius). Two species of Scymnus have been observed in association with RWA in small grain fields in the past; Scymnus morelleti was found within rolled, RWA-infested wheat leaves in South Africa (Aalbersberg et al., 1984), and Berest (1980) reported finding S. frontalis in RWA-infested wheat fields of the right bank steppe zone of Ukrain ian SSR. Naranjo et al. (1990) studied the development of S. frontalis in the laboratory. Little else is known about the biology of S. frontalis and more infor mation is needed in order to evaluate its potential as a biological control agent for the RWA. The purpose of our study was twofold. The first was to compare the quality of several aphid species as prey for S. frontalis by measuring immature development time and survival, and adult weight, survival and fecundity of individuals fed 1 Present address: 5902 West Gary Drive, Tempe, Arizona 85282. 2 USDA, ARS, Plant Science Research Laboratory, 1301 N. Western St., Stillwater, Oklahoma 74075. 3 USDA, ARS, Beneficial Insects Research Laboratory, USDA, 501 South Chapel Street, Newark, Delaware 19713. 4 Mention of a commercial or proprietary product does not constitute an endorsement by the USDA. Accepted for publication 1 November 1990. VOLUME 65, NUMBER 4 411 exclusively on each species as immatures. The second was to establish whether S. frontalis would preferentially eat RWA when allowed to choose between RWA and another cereal aphid species. Materials and Methods Adult S. frontalis were obtained from the USDA, ARS Beneficial Insets Re search Laboratory, Newark, Delaware, descended from beetles originally collected in Beypazari, Turkey, on 14-19 June 1988. For the first of two trials (23 November 1988), 100 eggs were collected during a 24-hour period. The adult beetles laid eggs readily on a cloth substrate which was then cut into squares, each containing a single egg. Eggs were placed in individual 4 5-ml capacity polystyrene vials (Daigger Scientific), and capped with white snap-caps with a 17-mm hole in the top covered with fine mesh screen. Eggs were incubated at 22?C ? 2?C and a 15:9 L:D cycle. Upon eclosi?n, first-instar S. frontalis larvae were separated into three, equal-sized groups and fed one of the following species of aphid: the greenbug, Schizaphis graminum (Rondani), RWA, or English grain aphid, Macrosiphum avenae (L.). Aphids were from colonies maintained in the greenhouse on wheat or barley seedlings. Larvae were maintained individually and fed an excess of aphids. Duration in days of larval and pupal stages and weights of newly emerged adults were recorded. For the second trial (5 January 1989), 126 eggs were collected as previously described. Conditions were the same for this trial except that larvae were fed either RWA, greenbug, or pea aphid, Acyrthosiphon pisum (Harris). The temperature was slightly higher, 24?C ? 2?C, but the photoperiod was the same as for the previous trial. Larval and pupal developmental times and weights of newly emerged adults were recorded. To determine fecundity and survival, individual newly emerged female beetles were randomly paired with a male in a 9-cm diameter, 7-cm tall, 400-ml capacity plastic container with a screen lid. Pairs were fed the same aphid species as immatures until 13 March 1989, when colonies of RWA and greenbug were depleted. After that date, all pairs were fed pea aphids. Each pair was given a 1-cm piece of moistened cotton wick daily as a water source and a 1-cm by 5-cm section of cloth as an oviposition substrate. Analysis of variance (PROC GLM, SAS Institute, Inc., 1982) was used to test for treatment differences. Each trial was analyzed separately to determine differ ences among S. frontalis fed different diets in mean fecundity, length of the larval and pupal stages, length of the pre-oviposition period, and adult weight. The following life table statistics, described by Birch (1948), were estimated: intrinsic rate of increase (rm), gross reproductive rate (GRR), net reproductive rate (R0), and mean generation time (MGT). A jackknifing algorithm (Meyer et al., 1986) was used to estimate rm. Use of this method facilitated calculation of standard errors of rm estimates and statistical comparison of estimates using ?-tests. In the field, S. frontalis would be exposed to a mixture of aphid species whereas in the above tests only one species was offered. It is possible that S. frontalis avoids feeding on RWA if other species are available. To test this possibility, a feeding choice test was conducted using newly hatched S. frontalis larvae. First and second-instar RWA or English grain aphid nymphs were obtained by gently sifting mixed-aged, laboratory-reared aphids through a fine mesh screen. Aphids were counted and placed in a 45-ml capacity plastic vial with a 4-cm piece of 412 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY Table 1. Mean developmental times of Scymnus frontalis immatures fed four different species of aphids. Each trial was analyzed separately, and letters were assigned to statistically significant pair

First Report of the Chinch Bug (Heteroptera: Lygaeidae) Egg Parasitoid Eumicrosoma beneficum Gahan (Hymenoptera: Scelionidae) in Nebraska

Abstract: A scelionid wasp, Eumicrosoma beneficum Gahan, was reared from chinch bug, Blissus leucopterus leucopterus (Say), eggs collected from wheat {Triticum aestivum L.) near Odell, Nebraska, in June 1989. Three-hundred twenty-one of 680 chinch bug eggs (47.2%) were parasitized by E. beneficum. Based on a subsample of 92 wasps the population was 64.1% female. This is the first report of this wasp from Nebraska. The chinch bug, Blissus leucopterus leucopterus (Say), has been recognized as a periodic pest of corn, wheat, sorghum and other grasses in the midwest for many years (Swenk, 1925; Shelford and Flint, 1943). Chinch bug populations were abundant in southeastern Nebraska (Spike et al., 1991), north eastern Kansas (Bell, 1991) and adjacent regions of Iowa and Missouri during 1988-1991. Nebraska sorghum growers have suffered crop losses from chinch bugs estimated at $11.3 and $10.0 million in 1989 and 1990, respectively (Spike et al., 1991). Recent research on management of chinch bugs in crops has focused on plant resistance (e.g., Meehan and Wilde, 1989), chemical insecticides (e.g., Mize et al., 1980) and to some extent biological control by the fungus, Beauveria bassiana (Balsamo) Vuillemin (e.g., Krueger et al., 1991). Other potential biological controls of chinch bugs are less well researched. 1 Current address: South Central Research and Extension Center, Box 66, University of Nebraska, Clay Center, Nebraska 68933.

Description of Nothotrichocera chiloe New Species, First Representative of the Genus in South America (Diptera: Trichoceridae)

Abstract: The genus Nothotrichocera Alexander, previously known from Tasmania and the subantarctic islands of New Zealand, is recorded from South America for the first time. A new species, N. chiloe, is described and illustrated from specimens collected from Isla Chiloe, Chile. Comparison is made between this species and other members of Nothotrich ocera. The genus Nothotrichocera includes six species occurring in the southern islands of Australia and New Zealand. The genus was proposed by Alexander (1926), and his four originally included species were Nothotrichocera cingulata, N. tasmanica, N. terebrella, and N. tonnoiri. All four species were described from Tasmania. Edwards and Keilin (1928) suggested a re-examination of the placement ofTricho cera antarctica (Edwards, 1923) from Campbell Island, New Zealand and later it was transferred to Nothotrichocera by Alexander (1955). The last species, N aucklandica, was described by Johns (1975) from Auckland Island, New Zealand. When first established, the genus was distinguished from other related genera by the features of the basitarsus, tibial spurs, and wing venation. Species of Noth otrichocera were characterized by having the basitarsus about one-half the length of the second tarsomere, absence of tibial spurs, wing anal angle indistinct and having the second anal vein curved. In describing N aucklandica, Johns brought attention to the structures of the male hypopygium for this species and N. antarcti ca (Edwards). Hypopygial characters had not been emphasized previously as informative taxonomic features at the species level in this genus because five of the six known species were originally described only from females. In recently acquired Chilean material in the collection of the Carnegie Museum of Natural History, two specimens were found to be the males of a new species belonging to this genus. It is the first representative of Nothotrichocera known from the Neotropical Region. Nothotrichocera chiloe, new species (Figs. 1-9) diagnosis: Small-sized winter crane flies. Second tarsomere 1.5 times longer than first. Male genitalia: balloon-like basistyles with sinuous projections, bridge lacking. Between basistyles a rounded structure present. Dististyle with basal process carrying a secondary process; phallosome very slender, parameres short, crossed. 1 Institute of Animal Systematics and Evolution, Polish Academy of Sciences, ul. Slawkowska 17, 30-016 Krakow, Poland. 2 Invertebrate Zoology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213. Accepted for publication 24 September 1991. This content downloaded from 157.55.39.183 on Fri, 22 Apr 2016 05:04:26 UTC All use subject to http://about.jstor.org/terms 186 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY