Wingless Morphs Research Articles

Density‐dependent regulation in populations of potato‐colonizing aphids

AbstractScarcity of long‐term (over 30 years) data series represents a major challenge for an accurate estimation of the role of density‐dependent processes in population regulation. We analyzed population densities of the wingless parthenogenic morphs of buckthorn aphid (BA), Aphis nasturtii Kaltenbach, potato aphid (PA), Macrosiphum euphorbiae (Thomas), and green peach aphid (GPA), Myzus persicae (Sulzer) from 1949 to 2003 for signs of density‐dependent regulation. We found strong evidence of density‐dependent regulation, with detection of density dependence being fairly consistent among the different statistical techniques. Direct density dependence was detected for the populations of all three species. There was also evidence of delayed density dependence for PA. The periodicity of population fluctuations for BA and GPA was 6.1 years and 3.9 years, respectively. The periodicity for PA was not explicit, being highly variable throughout the time series. Effects of density‐independent weather factors were relatively minor compared to density‐dependent regulation. The BA populations experienced a significant reduction in both density and annual oscillations starting in 1995, while GPA populations experienced a similar reduction in 1991. No such change was apparent for PA. The most likely explanation for the observed phenomenon is a change in the composition of the lady beetle community following the establishment of two alien coccinellid species, and/or changes in insecticide use by commercial growers in the area of the study.

Cephalic anatomy of Zorotypus hubbardi (Hexapoda: Zoraptera): new evidence for a relationship with Acercaria

External and internal head structures of Zorotypus hubbardi were examined. A detailed description is provided for the wingless morphs. The results are compared to the conditions found in alate specimens and in representatives of potentially related groups of insects. The pigmentation is strongly reduced in the wingless morphs and well-developed compound eyes, optic lobes and ocelli are absent. Kidney-shaped white spots between the paired ocelli and compound eyes were absent in all specimens examined. Most characters of the head (orthognathism, tentorium, musculature, mouthparts) are plesiomorphic. The wing and eye dimorphism, the strongly reduced head sutures, the reduced number of antennomeres, the presence of a prostheca on the left mandible and the presence of a transverse muscle of the head capsule and a retractor of the salivary sclerite are potential autapomorphies of Zoraptera. The unusual shape and large relative size of the brain and suboesophageal complex are also probably autapomorphic and a result of miniaturisation. Possible affinities with Dictyoptera were not supported by the results of this study. The only potential apomorphic feature of the head shared with Embioptera is the presence of a clearly delimited anteclypeus. However, this condition is also present in several groups of Acercaria. The very strongly developed M. clypeobuccalis, the medially divided prementum, and the slender, apically bifid laciniae without any mesally directed setae or spines are potential autapomorphies of Paraneoptera (incl. Zoraptera). If this group is indeed monophyletic, it is plausible to assume that the stem species was small like zorapterans and psocopterans and feeding on hyphae and spores of fungi, with mandibles with grinding molae and chisel-like laciniae suitable for loosening the food substrate. The feeding apparatus was then further modified within Acercaria, with a mortar-and-pistill apparatus in Psocoptera, and piercing–sucking mouthparts in Anoplura, Thysanoptera and Hemiptera.

On-Soil Movement and Plant Colonization by Walking Wingless Morphs of Three Aphid Species (Homoptera: Aphididae) in Greenhouse Arenas

Potato aphid, Macrosiphum euphorbiae (Thomas); green peach aphid, Myzus persicae (Sulzer); and buckthorn aphid, Aphis nasturtii Kaltenbach are polyphagous herbivores that commonly colonize potato plants, Solanum tuberosum L., in the northeastern United States and Canada. Their movement influences spatial and temporal patterns of viral spread within potato fields. We investigated aphid movement between potato plants early in the season, with a particular focus on their ability to walk over bare soil. On average, aphids survived 1.16 ± 0.04 d (mean ± SE) on the surface of bare soil; all of them dying within 3 d. Wingless aphids did not leave potato plants that were adequate as a food supply. When forcibly removed from the host plant and released on the soil surface, all three species colonized the nearest plant within 1 h. However, when given no other choice, a significant proportion of aphids was fully capable of colonizing potato plants as far as 180 cm away from the point of release. Potato aphid, which is the largest, was the most mobile of the three species. The green peach aphid was intermediately mobile, and the buckthorn aphid was the least mobile species.

The Endocrine Regulation of Wing Polymorphism in Insects: State of the Art, Recent Surprises, and Future Directions

The endocrine mechanisms controlling the development and reproduction of flight-capable (long-winged) and flightless (short-winged or wingless) morphs of wing-polymorphic insects have been intensively investigated. The "classical model," put forward in the early 1960s, postulates that morph-specific differences in development and reproduction are caused by variation in the titers of juvenile hormone (JH) and/or ecdysone. Despite decades of study, the importance of these hormones in regulating wing polymorphism in aphids and planthoppers remains uncertain. This uncertainly is largely a consequence of technical and size constraints which have severely limited the types of endocrine approaches that can be used in these insects. Recent studies in wing-polymorphic crickets (Gryllus) have provided the first direct evidence that the in vivo blood titers of juvenile hormone and ecdysone, and especially the activity of the JH regulator, juvenile hormone esterase, differ between nascent morphs. Morph differences are largely consistent with the classical model, although some types of data are problematic, and other explanations are possible. Adult morphs differ dramatically in the JH titer but titer differences are more complex than those proposed by the classical model. Detailed endocrine information is thus far available only for a few species of crickets, and the hormonal control of wing polymorphism for insects as a whole remains poorly understood. Future studies should continue to investigate the role of JH and ecdysteroids in morph development and reproduction, and should expand to include studies of morph-specific differences in hormone receptors and neurohormones.

Body colour and genetic variation in winged morph production in the pea aphid

AbstractAphids (Homoptera: Aphidoidea) produce a number of different phenotypes in their life‐cycle, among which are winged (alate) and wingless (apterous) morphs. Lowe & Taylor (1964) and Sutherland (1969a, b) were the first to suggest that aphid clones differ in their propensity to produce the winged morph and that in the pea aphid (Acyrthosiphon pisum Harris), this propensity is linked to the colour of the phenotype. We tested for the occurrence of genetic variation in winged morph production by rearing individuals from red and green clones of pea aphid under wing‐inducing (crowding) and control conditions, and scored the phenotypes of their offspring. Clones differed significantly in alate production and red clones produced on average a higher proportion of winged morphs than green clones. Importantly, however, there was considerable variation between clones of the same colour. Broad‐sense heritabilities of winged morph production were 0.69 (crowding treatment) and 0.63 (control). Clones also differed in the number of offspring they produced. When exposed to the crowding stimulus, aphids deferred offspring production, resulting in a higher number of offspring produced in the crowding treatment than in the control.

Effect of Fusarium, Paecilomyces and Trichoderma formulations against aphid Schizaphis graminum.

Fungal strains belonging to the genera Fusarium, Paecilomyces and Trichoderma were tested in vitro in order to study their effects against Schizaphis graminum, one of the major pests of cereal crops around the world. Biological assays were performed using a solid formulation that was obtained from fungal cultures grown on rice and then finely ground (<0.2 mm). The occurrence of toxic secondary metabolites (fumonisin B1 and beauvericin) produced by these fungi was also investigated. In each experiment, three groups of aphids: 15-hour old larvae, 5-day old nymphs with wing buds and wingless morphs were treated with a suspension of a fungal formulation. Some strains belonging to the genera Fusarium and Trichoderma significantly controlled the specimens of the three groups of S. graminum. The F proliferatum strain ITEM 1407, producing a high level of fumonisin B1 in the culture (1250 microg/g), and F larvarum strain ITEM 2139 had high insecticidal activity (>60%) within 10 minutes after application. As F. larvarum ITEM 2139 did not produce metabolites toxic to mammals, it might be a good candidate as a biocontrol agent of S. graminum in the field.

Factors influencing reproductive strategies of the vespid parasitoid Sphecophaga vesparum vesparum (Hymenoptera: Ichneumonidae)

The vespid wasp parasitoid Sphecophaga vesparum vesparum (Curtis) (Hymenoptera: Ichneumonidae) produces three types of cocoons, “white”, “weak‐walled yellow” and “yellow”. The adults that emerge from them represent a transition from wingless female morphs that emerge in a few weeks to alate females that remain dormant for 1–4 years. To determine the role of host age, nest temperature, and any intrinsic differences in the eggs on parasitoid cocoon type, newly emerged adult parasitoids were placed individually onto pieces of worker or queen comb containing Vespula vulgaris (L.) hosts of known age, and kept at different temperatures. Cocoon forms showed a continuous gradient in type rather than discrete morphs as was previously suggested. Cocoon type was principally determined by the age of the host on which the parasitoid oviposited; yellow cocoons resulted from eggs laid in early stages after the pupal cap was spun, and white cocoons from eggs laid on more developed pupae. Host age also influenced parasitoid cocoon weight. Temperature affected the rate of development of vespid immatures relative to the parasitoid, and so indirectly influenced cocoon type by altering the length of time parasitoid larvae were able to extract nutrients from developing wasp pupae. Low temperatures did not restrict cocoon production, as parasitoid cocoons developed at lower temperatures (19°C) than those at which the host could successfully complete development (lower limit between 25 and 26.3°C). There was no evidence of different parasitoid egg types, but adult parasitoids influenced cocoon type by preferential oviposition on host immatures that had recently spun caps. Only 20% of eggs laid produced weak‐walled yellow or white cocoons, which are the only cocoon types that reinfest the same nest. If this proportion reflects productivity in the field, then the spread of parasitoid populations within wasp colonies will be restricted. This effect will limit the impact of Sphecophaga as a biological control for Vespula spp.

Genetic variation within a parthenogenetic lineage.

A clone of the grain aphid Sitobion avenae F. was maintained parthenogenetically over thirty-two generations (n = 344) in a constant environment: a new generation being set up by a female selected at random from the preceding generation. Genomic DNA from individual aphids was screened for genetic stability using RAPD-PCR with a previously tested ten-mer primer. A putative germ-line mutation was noted in generation 14 and somatic mutations were noted in generations 12, 25, 27 and 29. There were no differences in the RAPD-PCR profiles of winged and wingless morphs and samples tested for symbiotic DNA. No endoblotic fungal organism was associated with the clone. Southern blotting and hybridization studies indicated that band additions were of aphid origin. However, the RAPD-PCR profiles of the germ-line and somatic mutation samples were unique from other aphid clones cultured during the experimental period. This paper documents discernible genetic changes occurring within an animal clonal lineage over time and Impacts on the consequences this may have for clonal systems.

Wing dimorphism of the water strider &lt;i&gt;Limnogonus franciscanus&lt;/i&gt; (Stål) (Heteroptera: Gerridae) in a seasonal tropical climate

The seasonal occurrence of wing morphs of Limnogonus franciscanus was studied in a mangrove swamp by taking monthly samples during nineteen months. Altogether 428 males and 413 females were collected. The percentage of winged individuals remained constant at ca. 3.2% throughout the study period. There were no differences between sexes in the proportions of winged and wingless morphs. The frequency of gravid females peaked during the rainy periods.

Genotypic variation among different phenotypes within aphid clones.

Most aphid species Hemiptera: Aphididae are parthenogenetic between periods of sexual reproduction. They are also highly polyphenic, with different adult morphs occurring in the life cycle, piz. winged, wingless, asexual and sexual. It is assumed that aphids born in a parthenogenetic clonal lineage are genetically identical regardless of the final adult form with the exception of sexual forms). Using the randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) we have found that different asexual adult phenotypes winged and wingless of some clones of two cereal aphid species (the grain aphid, Sitobion avenae (F.) and the bird-cherry aphid. Rhopalosiphum padi (L.) may be distinguished by the presence or absence of one or more RAPD-PCR bands. In three of nine clones examined, such differences were found, and Southern blotting and hybridization of the discriminating bands confirmed these to be of aphid origin, rather than due to endosymbiotic bacteria or contaminating fungi. The main 248 and 296 bp bands, in the two species respectively, were sequenced and found to be A/T rich. The smaller band showed 57% homology with white striated muscle over a stretch of 90 bp. Genomic DNA treated with dimethyl sulphoxide to remove secondary structures still showed differences in RAPD-PCR profiles between winged and wingless morphs within the unusual clones. This discovery may be widespread and therefore it is important to understand the phenomenon in relation to clonal organisms.

Cuticular hydrocarbons of winged and wingless morphs of the ectoparasitoid Choetospila elegans Westwood (Hymenoptera: Pteromalidae) and its host, larval lesser grain borer ( Rhyzopertha dominica) (Coleoptera: Bostrichidae)

1. 1. The cuticular hydrocarbons from winged and wingless morphs of Choetospila elegans, a larval ectoparasite of several internal-feeding stored product beetle pests, were characterized. 2. 2. All four morphs share the same cuticular hydrocarbons, with the major components being n-alkanes (C 21-C 33). 3. 3. The minor components are 3-, 11- and 13-methyl branched alkanes and Z-10-monoenes. 4. 4. Two-way analysis of variance (sex and wing morph) shows that males and females have the same profiles, whereas four components showed significant differences between wingtype morphs. 5. 5. Only one of these four hydrocarbons (n-C 31) was a major component. 6. 6. The cuticular hydrocarbons of larvae of the lesser grain borer, Rhyzopertha dominica, were also characterized. 7. 7. Although the beetles' major components were the same n-alkanes as those found on the adult parasites, their minor components were different. 8. 8. Thus, the beetle larvae have no alkenes, but instead have 3-, 11-, 13- and 15-methylbranched alkanes, as well as a series of 11,15-dimethylalkanes. 9. 9. A cuticular hydrocarbon profile obtained on a population of C. elegans winged females that had been reared on rice weevil larvae was nearly identical to that from winged females reared on the lesser grain borer larvae.

Key to the Middle Eastern species of Uroleucon Mordvilko (Aphididae: Homoptera)

Abstract. Keys are provided to distinguish the winged and wingless viviparous morphs of the thirteen species of Uroleucon (=Dactynotus) known from the Middle East. The host range and geographical distribution of each species is indicated.

DIFFERENCES IN SURVIVORSHIP, DEVELOPMENT RATE AND FERTILITY BETWEEN THE LONGWINGED AND WINGLESS MORPHS OF THE WATERSTRIDER, LIMNOPORUS CANALICULATUS.

Species of waterstriders (Gerridae: Hemiptera) exhibit a remarkable diversity in degree of winglessness (Vepsalainen, 1978; Calabrese, 1980; Zera, 1981). Some species consist exclusively of fully-winged individuals, while other species are composed almost exclusively of wingless individuals; many species exhibit the intermediate case of wing polymorphism and consist of various proportions of fully-winged, short-winged and/or wingless morphs. Wing-polymorphic species often exhibit dramatic spatial and/or temporal variation in morph ratios, both among populations of the same species and among species. Because of this diversity, waterstriders, especially wing polymorphic species, are ideal candidates for the study of the evolution of winglessness (or conversely, the evolution of dispersal). One of the major questions in the study of the evolutionary forces which influence wing polymorphism concerns fitness differences among the morphs. In many non-gerrids, dramatic differences between the fully-winged and the shortwinged or functionally equivalent (Anderson, 1973) wingless morph have been documented in a variety of fitness-associated traits (for reviews, see Harrison, 1980; Dingle, 1982). These include differences in such traits as survivorship under stress, duration of larval or nymphal development, age of first reproduction, and fecundity. Moreover, one of the most important results of these studies is the demonstration that differences in fitness traits are often consistently associated

Differences in Survivorship, Development Rate and Fertility Between the Longwinged and Wingless Morphs of the Waterstrider, Limnoporus canaliculatus

Differences in Survivorship, Development Rate and Fertility Between the Longwinged and Wingless Morphs of the Waterstrider, Limnoporus canaliculatus

GENETIC STRUCTURE OF TWO SPECIES OF WATERSTRIDERS (GERRIDAE: HEMIPTERA) WITH DIFFERING DEGREES OF WINGLESSNESS.

The Gerridae (Hemiptera: Insecta) is a worldwide family whose constituent species exhibit dramatic interand intraspecific variation in the degree of winglessness (Brinkhurst, 1960; Vepsaliiinen, 1978; Calabrese, 1979). At one extreme, the family contains species which are fully winged in all populations and during all seasons, while several species consist almost exclusively of wingless morphs over large geographical ranges and during all seasons. Many species exhibit the intermediate case of wing-polymorphism: the occurrence of various combinations of fully winged, partially winged and/or wingless morphs in the same population at the same time. Various wing-polymorphic species show differing patterns of spatial and/or temporal changes in morph ratios and patterns may vary both interand intraspecifically. The dramatic differences in frequency of winged morphs pose intriguing questions regarding the evolutionary forces responsible for degree of winglessness and the relationship between degree of winglessness and genetic structure of waterstrider species. One might expect genetic structure to be strongly influenced by degree of winglessness via reduction of flight dispersal ability and consequent reduced gene flow. Thus, species composed almost exclusively of wingless individuals should exhibit patterns of marked genetic differ-

Reproductive strategy of winged and wingless morphs of the aphids Sitobion avenae and Metopolophium dirhodum.

The reproduction of apterous and alate morphs of the aphids Sitobion avenae and Metopolophium dirhodum is compared on the basis of fecundity in 5- and 10-day periods of adult life. Apterae of both species are consistently more fecund than alatae of comparable weight, producing about three more nymphs on average in any 5-day period. The reproductive differences are related to the number and quality of embryos at eclosion and to ovulation rates, both of which in turn appear to be linked to wing-muscle maintenance. These relationships between weight, embryos and reproduction may be used to predict a newly moulted adult aphid's fecundity, a method which may facilitate the assessment of resistance to aphids in new cereal varieties, by obviating lengthy recording of reproduction. The strategies by which alatae of these and other aphid species minimize the difference between their fecundity and that of apterae are discussed.

Stereoscan views of some aphid mouthparts

The mouthparts, particularly the probosces of two aphid species, Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas), are compared with the use of the scanning electron microscope. The details of the setae on the terminal segments of the winged and wingless morphs are compared.