Ayala ed. Sinauer Associates, Massachusetts. Morphological and genetic differentiation in aphids Aphididae. Electrophoretic techniques for the genetic study of aphids, p. In: A. Harrewijn eds. Their biology, natural enemies and control. Elsevier Sc. Electrophoretic techniques for the genetic study of mosquitoes. News Electrophoretic comparison of aphid species: detecting differences based on taxonomic status and host plant. Genetic differentiation and its bearing on migration in North American populations of the corn leaf aphid, Rhopalosiphum maidis Fitch Homoptera: Aphididae. Enzyme variability in populations of aphids.
Enzyme polymorphism and taxonomy of aphid species. Searching for the source of the annual spring migrants of Rhopalosiphum maidis Homoptera: Aphididae in North America, p. In: J. Holman, J. Each species is dealt with in 1 or 2 pages, which include a summary treatment of its host plant's spectrum, pest status, damage caused, and life history.
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The general occurrence of each species is briefly described, and a distribution map is provided. Finally, a good drawing illustrating the most typical life stage of the pest concerned is given, sometimes unfortunately replaced by a picture of the damage. Although this sort of presentation is very convenient for individual species, it is highly confusing, sometimes misleading, when the several species of one genus are treated simultaneously see the genera Apion or Sitona for instance.
The fact that insect species do appear in alphabetical order in some families Curculionidae for instance, apart from a few exceptions , but are grouped according to the subfamilies in others Chrysomelidae, etc. In Chapter 10, finally, the major and minor pest species are listed for each particular crop, the cultivated plants being here again arranged in alphabetical order.
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- O Little Town of Bethlehem?
Certainly, some of the author's choices could be discussed why neglect the ornamentals, and cultivated plants like soya bean, safflower or cotton; pest species like Colaspidema atra and Diuraphis noxia; give minor pest status to Metopolophium dirhodum, etc.? Used as a complement to the "Agricultural Insect Pests of the Tropics" by the same author, this book will undoubtedly be of benefit to students, but of little help to the field practitioner. Minks and P. Harrewijn Editors. World Crop Pests, Vol. Aphids are probably the most widely-studied group of insects both by reason of their diverse biology and of their prime importance as agricultural pests.
Several excellent books have appeared in recent years on restricted aspects of our knowledge of aphids but, perhaps because of the vastness of the subject, a comprehensive work has never before been attempted. This multi-author series covers all aspects of aphids, the present volume being devoted mainly to morphology, biology and evolution.
The contributions by nineteen authors are integrated into a treatise covering wide-ranging topics within these headings. The section on external morphology is clearly illustrated with line drawings, bringing out the wide diversity of structures throughout the group. This is followed by an account of morphs and their structural variation, including photographs of grotesque soldier larvae. In the systematics section, former classifications are compared and evaluated, and morphological characters, used in determination, are described in detail.
It is, therefore, rather surprising that no attempt is made to include a key to at least the major pest species. The series of volumes is, after all, entitled "World Crop Pests", yet its usefulness as a comprehensive guide for the economic entomologist is here ignored. In the chapter on "Anatomy and Physiology", the alimentary tract and nervous system are illustrated by clear line drawings, the neurosecretory and endocrine systems by electron micrographs, and the sensory system by some striking scanning electron micrographs.
The text in each case, and in the sections on nutritional physiology and symbionts, is a thorough, yet concise and readable, review of the literature. Subsequently, one starved female O. The boxes were placed upside down on a tray covered with gauze in order to have the abaxial side of the discs facing downwards as on plants. Predation and oviposition rates were measured after the predators had been transferred.
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For analysis of oviposition rates, data from the first and second day were omitted to reduce the influence of pre-experimental conditions. Each treatment was replicated 11 times. All statistical analyses were done with GenStat Release Population dynamics of a the green peach aphid M. All three treatments received parasitoids A. The generalist predatory mite N. Population dynamics of a , b the parasitoid A.
See legend to Fig. Number of prey consumed by one-week-old adult females of O. Average daily oviposition rates of ten-day-old adult female O. We aimed to assess the impact of generalist predators involved in intraguild predation or hyperpredation on specialised natural enemies, herbivore densities and the yield in a sweet pepper crop. The hyperpredator N. However, releasing O. Thus, intraguild predation by O.
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Apparently, the effects of intraguild predation were outweighed by O. As expected, the hyperpredator N. This corresponds with an earlier study, where N. However, hyperpredation by the predatory mite Amblyseius swirskii Athias-Henriot on predatory midges clearly disrupted the biological control of aphids Messelink et al. Yet, caution should be exercised, because the effects of hyperpredation may depend on the densities of the predatory mites Messelink et al.
Not only aphids, but also thrips were strongly suppressed by O. Both pests were ultimately controlled in all treatments, but the treatments with predatory bugs had the lowest number of honeydew-contaminated fruits. It is not clear why thrips densities ultimately also went down in the treatment without thrips predators. The high aphid densities in this treatment possibly reduced plant quality and consequently thrips growth rates. Our results do not provide evidence for strong negative or positive effects of the generalist predators on parasitoids.
Possibly, such effects were not detected because of the repeated releases of adult parasitoids, which are invulnerable to predation.
However, females of A. The absolute numbers of parasitized aphids were much lower in treatments with predatory bugs than in the other treatments, likely because the number of aphids available for parasitism was reduced by aphid consumption by the predatory bugs. However, the predatory bugs probably also consumed parasitized aphids. Because equal numbers of parasitoids were released in all treatments, the parasitoid:aphid ratio was higher in the treatments with predatory bugs because of the lower number of aphids.
Thus, higher rates of parasitism were expected in the treatment with predatory bugs. This was not observed, perhaps as a result of intraguild predation of parasitized aphids by the predatory bugs. However, parasitoids may also have been less effective at these lower aphid densities because they had to spend more time on host searching. One explanation for the excellent aphid control with O. This so-called predator-mediated apparent competition between prey species can enhance pest control Karban et al. In addition to these prey, sweet pepper pollen probably also contributed to the establishment of the predatory bugs.
However, our laboratory experiment showed that adult predatory bugs did not exclusively prefer either of the two prey species, and reproduced on both prey species. Thus, the presence of thrips probably contributed to the control of aphids because it resulted in higher predatory bugs. The opposite effect, the presence of aphids resulting in a release of thrips from control, might also have occurred in the short-term, especially because the presence of aphids reduced predation on thrips by the predatory bugs.
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Increased densities of O. Indeed, midge densities were lowest in the treatment with predatory bugs, possibly caused by predation of midges by predatory bugs and by competition between bugs and midges for aphids. Thus the decreased midge densities might have released aphids from control, but this effect was apparently outweighed by the predatory bugs consuming aphids. Equilibrium theory on intraguild predation predicts that disruption of biological control only occurs when the intraguild prey is the better competitor for the shared pest than the intraguild predator Holt and Polis ; Janssen et al.
Although these predictions may not directly apply to dynamics at a shorter time scale Briggs and Borer , it is possible that our intraguild predator O. In that case, theory predicts that the intraguild prey should be outcompeted by the intraguild predator, and indeed, the midges tended to disappear in the treatment with predatory bugs Fig. Intraguild predation by predatory bugs on parasitoids and midges did not affect aphid control negatively. This corresponds with previous studies showing that intraguild predators may reduce densities of intraguild prey, but in general do not disrupt control of the shared prey Janssen et al.
Several studies with generalist predators found that predation rates increased in the presence of multiple prey species Lucas et al. Our laboratory experiment possibly indicates such effects for O. Although predation rates on thrips decreased in the presence of aphids, the opposite was not the case.
Thus, the total number of prey killed increased in the mixed diet relative to aphids as only prey. This effect was not caused by differences in prey density because ample prey was offered in all treatments. However, our study suggests that generalist predatory bugs, although potentially risky as intraguild predators, can play a major role in controlling aphids.
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They are able to respond rapidly to aphid infestations because of their continuous presence in a crop. One could argue that sufficient densities of these predators would even control aphids.