Izabela Lesna

Diet-dependent female choice for males with ‘good genes’ in a soil predatory mite

Female choice for mates with ‘good genes’ presupposes that some males have better genes than others. However, the resulting selection against inferior males causes such genetic variability to disappear. This paradox may be resolved when substantial variability is maintained at a balance between selection and mutation. Alternatively, populations may exhibit genetic polymorphisms maintained by frequency-dependent selection or hybrid vigour. Here we show that a local population of soil predatory mites exhibits genetic variation in preference for two prey species. We find that hybrids between selected preference lines are superior or inferior in population growth rate, depending on the composition of the diet. Finally, we show that females in this population mate disassortatively when hybrids are superior, but switch to assortative mating otherwise. Thus, mate choice varies with diet and is tuned to incorporate ‘good genes’ in the offspring, that is, genes that promote the population growth rate of the offspring on the same diet as that experienced by the parents. In this way, hybrid success and mate choice act together in maintaining or eliminating genetic polymorphism in local populations.

Below-ground plant parts emit herbivore-induced volatiles: olfactory responses of a predatory mite to tulip bulbs infested by rust mites

Although odour-mediated interactions among plants, spider mites and predatory mites have been extensively studied above-ground, belowground studies are in their infancy. In this paper, we investigate whether feeding by rust mites (Aceria tulipae) cause tulip bulbs to produce odours that attract predatory mites (Neoseiulus cucumeris). Since our aim was to demonstrate such odours and not their relevance under soil conditions, the experiments were carried out using a classic Y-tube olfactometer in which the predators moved on a Y-shaped wire in open air. We found that food-deprived female predators can discriminate between odours from infested bulbs and odours from uninfested bulbs or artificially wounded bulbs. No significant difference in attractiveness to predators was found between clean bulbs and bulbs either wounded 30 min or 3 h before the experiment. These results indicate that it may not be simply the wounding of the bulbs, but rather the feeding by rust mites, which causes the bulb to release odours that attract N. cucumeris. Since bulbs are belowground plant structures, the olfactometer results demonstrate the potential for odour-mediated interactions in the soil. However, their importance in the actual soil medium remains to be demonstrated.

Ecology meets plant physiology: herbivore-induced plant responses and their indirect effects on arthropod communities

Introduction Herbivory by arthropods induces a wealth of changes in the primary and secondary chemistry of plants (Karban and Baldwin 1997, Constabel 1999, Agrawal et al. 1999, Kessler and Baldwin 2002). These chemical changes in turn do not only affect the inducer, but also other herbivore species attacking the induced plant (Denno et al. 1995, Denno and Kaplan Chapter 2 this volume). This effect of one herbivore species on other herbivores is called “indirect,” because it can only arise via the plant as an intermediate organism (Wootton 1994). Moreover, it is called trait-mediated, because the immediate effect of herbivory is an induced change in plant quality, not in plant quantity (Werner and Peacor 2003, Schmitz et al. 2004). The herbivore-induced state of plants may influence the community of arthopods that live on them. When the induced plant allocates much of its energy in compensatory growth or defense specifically aimed at the inducer, other herbivore species may profit from the increased nutritional quality or weakened defense of the plant, thereby giving rise to interspecific aggregations of herbivores on individual plants (Denno et al. 1995). If, however, the induced plant mounts a sufficiently generalized defense, the plant becomes “vaccinated” against attack by other herbivores, leading to species-poor communities of herbivorous arthropods on the plant (Karban and Baldwin 1997). Much the same reasoning applies to herbivore genotypes within a single species.

Candidate predators for biological control of the poultry red mite Dermanyssus gallinae

The poultry red mite, Dermanyssus gallinae, is currently a significant pest in the poultry industry in Europe. Biological control by the introduction of predatory mites is one of the various options for controlling poultry red mites. Here, we present the first results of an attempt to identify potential predators by surveying the mite fauna of European starling (Sturnus vulgaris) nests, by assessing their ability to feed on poultry red mites and by testing for their inability to extract blood from bird hosts, i.e., newly hatched, young starlings and chickens. Two genuine predators of poultry red mites are identified: Hypoaspis aculeifer and Androlaelaps casalis. A review of the literature shows that some authors suspected the latter species to parasitize on the blood of birds and mammals, but they did not provide experimental evidence for these feeding habits and/or overlooked published evidence showing the reverse. We advocate careful analysis of the trophic structure of arthropods inhabiting bird nests as a basis for identifying candidate predators for control of poultry red mites.

Biological control of the bulb mite, Rhizoglyphus robini, by the predatory mite, Hypoaspis aculeifer, on lilies: predator-prey interactions at various spatial scales.

Experiments in closed jars with lily bulbs showed that the predator, Hypoaspis aculeifer, can suppress populations of its prey, the bulb mite Rhizoglyphus robini, to very low levels. When the bulbs were decomposed into scales, the prey was suppressed earlier, supposedly because of increased accessibility to the sites where bulb mites reside. Repeating the experiment in open jars also led to strong suppression of the prey population: the predators did not leave the jars until almost all prey was eaten. To assess the possibility for biological control of bulb mites in lilies at a larger spatial scale, experiments were carried out in closed plastic bags filled with lily bulb scales and vermiculite, as is common practice in lily bulb propagation. The results showed that H. aculeifer was able to suppress its prey to very low densities, but probably due to a more complex spatial structure (i.e. vermiculite), prey suppression took longer. The results of these small- and large-scale population experiments suggest that local predator-prey interactions are very unstable despite the presence of refuges and spatial complexity. At which spatial scale complexity becomes large enough to cause spatial decoupling of the predator-prey interactions and thereby promote predator-prey persistence rather than prey extinction, will be the subject of future investigations.

Molecular phylogenetic assessment of host range in five Dermanyssus species

Given that 14 out of the 25 currently described species of Dermanyssus Dugès, 1834, are morphologically very close to each another, misidentifications may occur and are suspected in at least some records. One of these 14 species is the red fowl mite, D. gallinae (De Geer, 1778), a blood parasite of wild birds, but also a pest in the poultry industry. Using molecular phylogenetic tools we aimed to answer two questions concerning host specificity and synanthropicity: (1) is D. gallinae the only species infesting European layer farms?, and (2) can populations of D. gallinae move from wild to domestic birds and vice versa? Mitochondrial cytochrome oxidase I gene sequences were obtained from 73 Dermanyssus populations collected from nests of wild European birds and from poultry farms and these were analyzed using maximum parsimony and Bayesian inference. Mapping of the observed host range on the obtained topology and correlation with behavioural observations revealed that (1) host range is strongly dependent on some ecological parameters (e.g. nest hygiene, exposure to pesticides and predators), that (2) out of five species under test, synanthropic populations were found only in lineages of D. gallinae, and that (3) at least some haplotypes found in wild birds were very close to those found in association with domestic birds.

Size of predatory mites and refuge entrance determine success of biological control of the coconut mite

Predators face the challenge of accessing prey that live in sheltered habitats. The coconut mite Aceriaguerreronis Keifer (Acari: Eriophyidae) lives hidden beneath the perianth, which is appressed to the coconut fruit surface, where they feed on the meristematic tissue. Its natural enemy, the predatory mite Neoseiuluspaspalivorus De Leon (Acari: Phytoseiidae), is larger than this pest and is believed to gain access to the refuge only after its opening has increased with coconut fruit age. In the field, experimentally enlarging the perianth-rim-fruit distance beyond the size of the predators resulted in earlier predator occurrence beneath the perianth and lower numbers of coconut mites. On non-manipulated coconut fruits, the predators gained access to the prey weeks later than on manipulated ones, resulting in higher pest densities of coconut mites. Successful biological control thus critically hinges on the size of the predator relative to the opening of the prey refuge.

Genetic polymorphism in prey preference at a small spatial scale: a case study of soil predatory mites (Hypoaspis aculeifer) and two species of astigmatic mites as prey

Arthropod predators usually feed on a variety of different prey types. At one extreme populations consist of an ensemble of pure specialists for each prey type and at the other they are composed of generalists that indiscriminately seize any prey encountered. In between these extremes populations may be composed of generalist predators with learned or genetically fixed prey preferences. Here, we report on experimental evidence for genetic variation in prey preference in a local population of the haplo-diploid, soil-inhabiting predatory mite, Hypoaspis aculeifer. A sample of c. 150 predatory mites obtained from c. 0.25 m2 sandy soil in a lily field (North-Holland), was collected and their offspring was subjected to two-way selection for prey choice, using two species of astigmatic mites as prey (Rhizoglyphus robini and Tyrophagus putrescentiae, further referred to as prey R and prey T). Individual female predators choosing exclusively prey R or exclusively prey T in three 10-minute dualchoice tests carried out at three-day intervals were set apart and reared (on prey T) as isofemale lines. Four generations of selection yielded three lines showing a high probability of choosing prey R and two lines choosing prey T. Cross-breeding in both directions resulted in hybrid females with intermediate preferences and the choices found in females from F1xParent backcrosses were best explained by assuming monogenic inheritance without dominance, Our selection and cross-breeding experiments demonstrate that polymorphism in prey preference can occur at a very small spatial scale within a local population. We discuss how such variability will alter the dynamics of otherwise monomorphic predator-prey models, and how the simple mode of inheritance of a preference trait can aid the evolution of ecotypes.

Diet-dependent female choice for males with |[lsquo]|good genes|[rsquo]| in a soil predatory mite

Female choice for mates with ‘good genes’ presupposes that some males have better genes than others. However, the resulting selection against inferior males causes such genetic variability to disappear. This paradox may be resolved when substantial variability is maintained at a balance between selection and mutation. Alternatively, populations may exhibit genetic polymorphisms maintained by frequency-dependent selection or hybrid vigour. Here we show that a local population of soil predatory mites exhibits genetic variation in preference for two prey species. We find that hybrids between selected preference lines are superior or inferior in population growth rate, depending on the composition of the diet. Finally, we show that females in this population mate disassortatively when hybrids are superior, but switch to assortative mating otherwise. Thus, mate choice varies with diet and is tuned to incorporate ‘good genes’ in the offspring, that is, genes that promote the population growth rate of the offspring on the same diet as that experienced by the parents. In this way, hybrid success and mate choice act together in maintaining or eliminating genetic polymorphism in local populations.