Ecological Entomology

BALE, J. S.; HARRINGTON, R.; CLOUGH, M. S.

doi: 10.1111/j.1365-2311.1988.tb00340.xpmid: N/A

ABSTRACT. 1 The mean supercooling points of first instar and adult Myzus persicae (Sulzer) maintained at 20°C and cooled at 1°C min−1 were −26.6 and −25.0°C respectively. 2 The LT50 (temperature) of the same age groups drawn from the same population and cooled at the same rate were −8.1 and −6.9°C, indicating extensive pre‐freeze mortality in M.persicae under laboratory conditions. 3 Acclimation at 10 and 5°C did not affect supercooling but depressed the LT50 of both first instars and adult aphids. 4 Freezing of leaves during feeding did not increase mortality above that expected from the direct effects of low temperature. 5 The level of cold in different winters can be expressed in terms of the total number of frost days, and the frequency of abnormally cold days. Winter temperatures differ markedly in a vertical profile from the soil to the soil or grass surface, and then to the air (and foliage) above. 6 The time of the first record of M.persicae in suction trap samples is correlated with January and February temperatures except in the west of England and Wales. Further north December and January temperatures are relatively more important. 7 Winter temperatures and the resultant aphid mortality is a primary determinant of the timing of the spring migration.

BULTMAN, THOMAS L.; FAETH, STANLEY H.

doi: 10.1111/j.1365-2311.1988.tb00341.xpmid: N/A

ABSTRACT. 1 We measured solar radiation reaching ten Quercus emoryi Torr. trees and recorded densities of four leaf‐mining insect species on these trees from June until September 1982. 2 The measurements showed that densities of two leaf miner species were negatively correlated with solar radiation. 3 In a field experiment, polypropylene shade fabric was suspended 1.3 m above four experimental trees to test for effects of reduced sunlight. 4 Leaves of experimentally‐shaded trees were heavier and contained lower percentages of proteins and gallotannins than leaves of control, sun trees, while per cent foliar monomeric, polymeric, and total phenols, and water content did not differ between sun and shaded trees. 5 Two of four leaf miner species had greater densities on experimentally‐shaded trees than sun trees. One of these two species experienced lower survivorship on sun trees owing to high levels of death from unknown causes on sun trees. 6 Two leaf miner species had greater densities on sun trees. One of these species had higher survivorship on shaded trees owing to high levels of parasitism on sun trees. 7 We conclude that even subtle differences in shading influences leaf miner density and mortality; however, the effects of shading vary from positive to negative among leaf miner species.

DREISIG, HANS

doi: 10.1111/j.1365-2311.1988.tb00342.xpmid: N/A

ABSTRACT. 1 In a given ant species, the number of ants collecting honeydew in an aphid colony or extrafloral nectar on a plant is proportional to the productivity of the colony or plant. Thus, the number of ants per resource unit and the ingestion rate per ant are constant for a species. 2 Mean number of ants per resource unit and ingestion rate per ant differed considerably between the investigated species. The ingestion rate increases with the body size of the species and decreases with an increase of the mean number of ants per resource unit. 3 Ingestion rates were higher in ants foraging singly at the resource than in ants foraging in the normal way in a group. 4 It is suggested that the ingestion rate per ant is reduced below a maximum level by the number of ants present per resource unit because a certain number of ants is needed to defend the resource against alien ants. Small species need more individuals for this purpose than large species, and consequently suffer a larger reduction of their ingestion rate.

ERNSTING, G.; WERF, D. C.

doi: 10.1111/j.1365-2311.1988.tb00343.xpmid: N/A

ABSTRACT. 1 Partial consumption of prey and prey size preference were studied in females of the carabid Notiophilus biguttatus F., using different size‐classes of the springtail Orchesella cincta (L.) as prey. 2 Time to ingest a prey increases disproportionately with prey size, mainly as a consequence of satiation. 3 During consumption of a prey the predator's rate of ingestion decreases, partly because of diminishing returns from the prey over feeding time. 4 The hypothesis that the diminishing returns from the prey induce partial consumption was refuted. 5 Partial consumption in the beetle is due to gut limitation; its occurrence depends on prey size. 6 Average weight of prey remains in four prey size classes were close to weights expected from average intercatch intervals and estimates of hunger. 7 Prey choice depends on level of food deprivation. 8 Partial consumption of prey, prey size preference and profitability of prey in relation to hunger of the beetle are discussed.

JOHNSON, MICHAEL D.

doi: 10.1111/j.1365-2311.1988.tb00344.xpmid: N/A

ABSTRACT. 1 The female of the solitary bee Ceratina calcarata (Robertson) (Hymenoptera: Anthophoridae) excavates a tunnel in a pithy twig and then constructs and provisions a linear series of brood cells that make up her nest. 2 Adult females are, on the average, 1.3 times heavier than the males, a significant difference (P<0.001). There is no difference between the sexes in the amount of weight gained per unit of larval food. 3 Larger females occur because their provision masses are, on the average, 1.3 times heavier than male‐producing provision masses, a significant difference (P<0.001). 4 Because mothers invest more time and energy in their daughters, Fisher's theory predicts that they should produce more sons. When available resources are fewer in a given year as reflected in lighter provision masses, more males are produced during the year. 5 The observed sex ratio did not differ significantly from the expected, calculated as mean female weight/mean male weight and was male‐biased. 6 Unlike species which nest in pre‐formed tunnels, the sex of any brood cell except the innermost is random with respect to that cell's position in the nest and the tunnel's depth and diameter. The innermost position contained offspring with a female biased sex ratio (P<0.005).

MAY, PETER G.

doi: 10.1111/j.1365-2311.1988.tb00345.xpmid: N/A

ABSTRACT. 1 I studied flower selection and foraging energetics of Agraulis vanillae L. (Nymphalidae) and Phoebis sennae (Pieridae), two butterfly species common to north central Florida. I identified the major nectar resources exploited by several populations of these butterflies and, for each plant species, measured available nectar volumes and concentrations, corolla lengths, and density. I quantified foraging behaviour of each butterfly species at each nectar source (flower visitation rate and percentage of foraging time in flight), and used these data to estimate the net rate of energy intake of each butterfly species at each nectar source. 2 Estimated mean energy contents of individual flowers of the eleven exploited plant species spanned three orders of magnitude, ranging between 0.015 and 9.27 joules. Mean energy content of individual flowers was strongly correlated with mean foraging profit of both butterfly species. 3 Mean nectar volume strongly influenced energy content and varied widely within and among species, ranging from 0.0076 to 1.853 μ1. Nectar concentration varied between 17.1% and 40.4% sucrose‐equivalents. Nectar volume was the best single predictor of foraging profitability (correlation coefficients of 0.994 and 0.984 for Phoebis and Agraulis respectively). Corolla length also strongly affected foraging profitability for both butterfly species; flower species with longer corollas were generally more profitable. 4 Flower density and nectar concentration showed weak or nonsignificant associations with foraging profitability. 5 The usefulness and limitations of these floral characteristics as bases for foraging selectivity, and the selective pressures foraging butterflies might place on the visited plants are discussed.

McLACHLAN, ATHOL J.

doi: 10.1111/j.1365-2311.1988.tb00346.xpmid: N/A

ABSTRACT. 1 Rain‐pools on granite exposures are common in tropical Africa and they are inhabited by the larvae of two midge species, Chironomus imicola Kieffer and Chironomus pulcher Wiedemann. 2 These pools differ from other ephemeral island habitats such as carrion, fallen fruit, sap flows, mushrooms and dung in their high degree of spatial predictability. Most pools are predictably inhabited by either C.imicola or C.pulcher. This finding is considered in the light of contemporary competition theory. 3 An arrangement whereby the same species repeatedly invades the same temporary habitat indicates that there is something about the habitat itself causing the discrimination. I suggest that degree of exposure to sunlight may provide a cue allowing females to discriminate between pools as oviposition sites. 4 Both species survive the long dry season by retreating to pools of river water left by receding rivers. Dispersal to rain‐pools by emerging adults occurs during the following season with imicola occupying rain‐pools remote from shaded rivers. Appropriately, measured against pulcher, the biology of imicola is that of a colonizing species. 5 The possibility is discussed that the chironomids in rock‐pools do not survive to breed. Instead, these populations may be maintained externally, for example by invasions from breeding populations in the Great Lakes of Africa, where larval densities may be too low to be detected by sampling. The evolutionary implications of such a situation are considered.

PRICE, PETER W.; PSCHORN‐WALCHER, H.

doi: 10.1111/j.1365-2311.1988.tb00347.xpmid: N/A

ABSTRACT. 1 Data mostly from the published literature were used to assess the effect of galling on the number of parasitoid species per host species in the phylogeny of nematine sawflies from free external feeders (colonial and solitary) to leaf gallers and shoot gallers. 2 The strongest effects of galling were the total elimination of the species‐rich cocoon‐attacking guild of parasitoids, and eonymphal parasitoids, from the parasitoid community on shoot gallers, all of which are in the genus Euura. 3 All tachinid larval parasitoids were also eliminated by the galling habit. 4 The cumulative effects of these exclusions resulted in a decline in mean number of parasitoid species per host species from almost sixteen species on external colonial feeders to 4.0 species on shoot gallers. 5 General patterns in per cent parasitism by non‐tachinid and tachinid larval parasitoids, eonymphal and cocoon parasitoids, on exposed feeders to shoot gallers, showed declines in non‐tachinid attack and elimination of tachinid, eonymphal and cocoon parasitoids. But leaf gallers tended to be attacked more than exposed feeders by non‐tachinid larval parasitoids. 6 The galling habit had a long‐term impact by reducing the number of parasitoid species attacking nematine sawfly gallers and per cent mortality inflicted, so that natural enemies may have been important as a selective factor in the evolution of galling nematine sawflies.

ROBERTSON, HAMISH G.

doi: 10.1111/j.1365-2311.1988.tb00348.xpmid: N/A

ABSTRACT. 1 Predation of Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) eggs by ants was studied for a summer and a winter generation on prickly pear Opuntia ficus‐indica (L.) Miller plants in the field. 2 Egg Predation between plants was spatially density‐dependent in the winter but not in the summer generation. 3 To test for the presence of delayed density‐dependent mortality within generations, percentage egg Predation during 5‐day periods was plotted against the number of eggs available in each period. Data points joined in a time sequence moved in an anticlockwise direction in the summer generation, suggesting a delayed density‐dependent response by the ants, whereas in the winter generation the points moved in a clockwise direction. 4 The degree of coincidence of the C. cactorum eggs with the peak larval production periods of the ants is suggested as the main reason for the temporal changes in egg Predation.

DRIESCHE, R. G.; BELLOWS, T. S.

doi: 10.1111/j.1365-2311.1988.tb00349.xpmid: N/A

ABSTRACT. 1 A technique for quantifying mortality due to insect parasitoids in insect populations is presented. The method is based on the measurement of recruitment to both the host susceptible stage and the pool of parasitized hosts. 2 The technique provides estimates of generational mortality due to parasitism and, when combined with estimates of population density, provides estimates of other mortality rates acting on both host and parasitoid populations. Such estimates are available both for the generation as a whole and for separate sampling periods. 3 The method is illustrated by application to two generations of Pieris rapae L. (Lepidoptera: Pieridae) and its larval parasitoid Cotesia (Apanteles) glomerata (L.) (Hymenoptera: Braconidae).