The induction of normal and teratoid viviparae by a juvenile hormone and kinoprene in two species of aphids

ABSTRACT. Topical application of a juvenile hormone (JH1) and the JH mimic, kinoprene, to short-day, ovipara-producers of Megoura viciae usually leads to the production of oviparous/viviparous intermediate forms in the progeny sequence, in place of the expected sexual females (oviparae). The ovaries of these abnormal forms may contain embryos rather than the haploid yolky eggs of oviparae; 'mixed' ovaries containing both haploid eggs and embryos are also observed. The intermediates range in form from winged (alate) to wingless (apterous). The fully alate individuals usually contain only parthenogenetic ovaries but differ from the naturally occurring alate viviparae in that they are invariably infertile, have fewer antennal sense organs and often bear pheromone releasing glands on the metathoracic tibiae. The hormonally induced production of normal viviparae is difficult in this species but has been achieved by rearing short-day aphids on kinoprene-treated bean plants.
In Aphis fabae similar oviparous/viviparous teratomorphs have been reported and, in addition, single JH1 treatments were shown to induce normal viviparae at the end of the progeny sequence. Multiple applications, beginning prenatally and continuing through the postnatal development of the gynopara (winged ovipara-producer), showed that the numbers of viviparae born were related to the earliness of the treatment and to the dosage. The results are compared with the effect of a switch in photoperiod and discussed in relation to the endocrine control of aphid polymorphism.     

The effect of juvenile hormone on host-plant preference in the black bean aphid, Aphis fabae

ABSTRACT. When offered the choice between a germinating tick bean (summer host) and a detached spindle leaf (winter host) adult gynoparae of Aphis fabae Scop. showed a distinct preference for spindle, as judged by site of larviposition. However, when offered the same alternatives, all four larval instars showed a settling preference for bean. A switch in host preference therefore occurs at or shortly after final (fourth) moult. Fifth instar, supernumerary larvae induced by juvenile hormone (JH I) treatment also preferred bean, indicating that the host preference switch at the fourth moult had been inhibited. Larval/adult intermediate forms produced by JH I treatment, but which were capable of parturition, showed a significant increase in the acceptability of bean as a larviposition site. Acceptability was proportional to the degree of juvenilization. Thus, although larviposition is an adult prerogative, JH I can influence the preferred site. This may, however, be an indirect effect which reflects a juvenilized settling preference.     

Hygroreception in olfactometer studies

Abstract In olfactometric studies, a technique used to measure insect behavioural bias towards airborne chemicals, many of the factors that could affect the bioassay outcome other than the volatiles themselves are carefully controlled (e.g. lighting conditions, temperature, spatial position, physiological state of the insects, time of day when the bioassay is performed) but one factor, namely humidity, is overlooked frequently when studying responses to plant volatiles. Many insect species respond positively and negatively to changes in humidity and, during bioassays, differences arising from odour choices with different water vapour release rates might have confounding effects versus the original intent of the behavioural study. The present study aims to assess the effect of different substrates on the water vapour content of air in an olfactometer‐like set‐up. The results show that airflow humidity is affected by the odour source used in the olfactometer air flow. In addition, the response of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae) is studied towards different humidities and plant material in an olfactometer. The present study suggests that humidity needs to be controlled in olfactometric studies.     

Landscape genetics of California mule deer (Odocoileus hemionus): the roles of ecological and historical factors in generating differentiation

Landscape genetics is an emerging discipline that utilizes environmental and historical data to understand geographic patterns of genetic diversity. Niche modelling has added a new dimension to such efforts by allowing species–environmental associations to be projected into the past so that hypotheses about historical vicariance can be generated and tested independently with genetic data. However, previous approaches have primarily utilized DNA sequence data to test inferences about historical isolation and may have missed very recent episodes of environmentally mediated divergence. We type 15 microsatellite loci in California mule deer and identify five genetic groupings through a Structure analysis that are also well predicted by environmental data. We project the niches of these five deer ecotypes to the last glacial maximum (LGM) and show they overlap to a much greater extent than today, suggesting that vicariance associated with the LGM cannot explain the present-day genetic patterns. Further, we analyse mitochondrial DNA (mtDNA) sequence trees to search for evidence of historical vicariance and find only two well-supported clades. A coalescence-based analysis of mtDNA data shows that the genetic divergence of the mule deer genetic clusters in California is recent and appears to be mediated by ecological factors. The importance of environmental factors in explaining the genetic diversity of California mule deer is unexpected given that they are highly mobile species and have a broad habitat distribution. Geographic differences in the timing of reproduction and peak vegetation as well as habitat choice reflecting natal origin may explain the persistence of genetic subdivision.     

Histocompatibility Gene Organization and Mixed Lymphocyte Reaction

TRANSFORMATION of allogenic lymphocytes in mixed cultures depends chiefly on an incompatibility between the lymphocyte donors at the major histocompatibility locus in man (HL-A), mouse (H-2) and rat (H-l)¹. Although the mouse H-2 locus can be divided into several regions each of which controls one or more antigenic specificities² and two or more subloci control HL-A antigens in man³, it is not known whether all parts of the major histocompatibility locus are equally important in eliciting transformation in mixed lymphocyte cultures. We now show that capacity to elicit lymphocyte transformation is different for different parts of the mouse H-2 locus.     

Development of microsatellites for the peat moss Sphagnum capillifolium using ISSR cloning

Sphagnum mosses are major components of peat bogs but populations of many species are under threat due to habitat fragmentation resulting from the cutting of peat for fuel. We have used an intersimple sequence repeat (ISSR)‐based cloning method to develop nine polymorphic nuclear microsatellites for the peat moss species Sphagnum capillifolium. Between three and seven alleles per locus were detected in a sample of 48 haploid gametophytes and levels of gene diversity ranged from 0.5391 to 0.7960. These represent the first microsatellite markers developed for this important genus and most also exhibited cross‐species amplification across a range of common Sphagnum species.     

Conservation and ecological implications of the use of space by chilla foxes and free‐ranging dogs in a human‐dominated landscape in southern Chile

We investigated whether domestic dogs (Canis lupus familiaris) influenced the use of space by chilla foxes (Lycalopex griseus) in southern Chile and tested the hypothesis that dogs interfere with chillas. We used scent stations and occurrence of scats within systematically placed plots to assess habitat use by both species and to test whether dogs were associated to the use of space by chillas. Activity data were obtained from captures for both species, and telemetry for foxes. Diet of both species was analysed in order to tease out the potential existence of exploitation competition. We found that, when active, chillas used prairies more and native forest less than expected according to availability, whereas inactive chillas (during the day) preferred native forest, the only habitat type that dogs did not use. The odds of dog occurrence increased at shorter distance to human houses, whereas the inverse pattern was observed for chillas. Poisson models showed that the number of chilla visits to scent stations was negatively correlated with the number of dog visits. We observed dogs persecuting and/or killing chillas which was also corroborated by local people that used dogs to prevent chilla‐related poultry losses, supporting the idea that dogs harass foxes actively. The analysis of scats showed that dogs fed mainly on house food and domestic ruminant carcasses whereas foxes fed on hare, hens, mice and wild birds, thus suggesting that exploitation competition is not a strong alternative hypothesis as a proximate cause for the patterns observed. We conclude that dogs seem to constrain the use of space by wild carnivores via interference.     

Development of microsatellites for the invasive riparian plant Impatiens glandulifera (Himalayan balsam) using intersimple sequence repeat cloning

Impatiens glandulifera (Himalayan balsam) is an invasive riparian plant species that can outcompete native perennials. Population genetic data on dispersal may aid in the management of invasive species, so we have developed microsatellite markers for this significant invader using an intersimple sequence repeat (ISSR)‐based cloning method. Eight polymorphic markers displayed between two and five alleles, with overall levels of observed and expected heterozygosities ranging from 0.0500 to 0.7500 and from 0.1449 to 0.7692, respectively.     

Flight behaviour of the bird cherry aphid, Rhopalosiphum padi

Abstract Seasonal winged forms of the bird cherry aphid, Rhopalosiphum padi L., were flown in an automated flight chamber. During their maiden flights, autumn migrants (gynoparae) had a greater initial rate of climb than summer (exules) and spring migrants (emigrants). Autumn migrants, presented with a laterally-positioned green-illuminated target for 2.5 s during each minute of flight, flew for a longer period before responding to the target (110 min) than summer migrants (36 min), while spring migrants responded after an intermediate time (72 min). This period is equivalent to the migratory phase of flight. The summer migrants were maximally responsive to targets illuminated by green monochromatic light (X, 555 nm). Targets illuminated with ultraviolet (γλ 360 nm) were attractive during the migratory and green-responsive phases of flight, but infrared (γλ700 nm) wavelengths were not attractive. The results are discussed with respect to aphid behaviour in the field.     

Transgenic Crops: The Next Generation, or an Example of 2020 Vision

Genetically modified, i.e. transgenic crops, are now being grownon several million acres throughout the world, mainly in NorthAmerica. Most of these ‘first generation’ productshave specific agronomic traits designed to improve the efficiencyof production. For example herbicide tolerant soybean and insectresistant corn are the two most widely grown transgenic crops.Increasingly, the new transgenic varieties under test containproduct quality or other higher value traits intended to providespecific benefits to the end user whether it be the producerof specialist chemicals or the consumer. This review describesexamples of these ‘second generation’ traits andattempts to predict the range of household, medical, industrialand environmental products that might become available overthe next 20 years. Copyright 1999 Annals of Botany Company Transgenes, transgenic plants, genetically modified plants, genetically modified food, plant breeding.