L.P.S. van der Geest

Diseases of mites

An overview is given of studies on diseases of mites. Knowledge of diseases of mites is still fragmentary but in recent years more attention has been paid to acaropathogens, often because of the economic importance of many mite species. Most research on mite pathogens concerns studies on fungal pathogens of eriophyoids and spider mites especially. These fungi often play an important role in the regulation of natural mite populations and are sometimes able to decimate populations of phytophagous mites. Studies are being conducted to develop some of these fungi as commercial acaricides.Virus diseases are known in only a few mites, namely, the citrus red mite and the European red mite. In both cases, non-occluded viruses play an important role in the regulation of mite populations in citrus and peach orchards, respectively, but application of these viruses as biological control agents does not seem feasible. A putative iridovirus has been observed in association with Varroa mites in moribund honeybee colonies. The virus is probably also pathogenic for honeybees and may be transmitted to them through this parasitic mite.Few bacteria have been reported as pathogens of the Acari but in recent years research has been concentrated on intracellular organisms such as Wolbachia that may cause distorted sex ratios in offspring and incompatibility between populations. The role of these organisms in natural populations of spider mites is in particular discussed. The effect of Bacillus thuringiensis on mites is also treated in this review, although its mode of action in arthropods is mainly due to the presence of toxins and it is, therefore, not considered to be a pathogen in the true sense of the word.Microsporidia have been observed in several mite species especially in oribatid mites, although other groups of mites may also be affected. In recent years, Microsporidia infections in Phytoseiidae have received considerable attention, as they are often found in mass rearings of beneficial arthropods. They affect the efficacy of these predators as biological control agent of insect and mite pests. Microsporidia do not seem to have potential for biological control of mites.

Effect of diets on the haemolymph proteins of larvae of Pieris brassicae

Abstract The protein concentration of the haemolymph of Pieris brassicae larvae reared on cabbage and on two different artificial media was determined. Although the development of larvae on the artificial diets was found to be slower, no statistically significant difference could be observed in the total protein concentrations of the haemolymph of larvae fed on cabbage and of those fed on the artificial media. Differences in pigmentation of the haemolymph of larvae on cabbage-containing diets and of the haemolymph of larvae which are fed on an artificial medium without cabbage could be explained by assuming a direct uptake of carotenoid compounds from the food by the insect.

The role of Orius vicinus Ribaut (Heteroptera; Anthocoridae) as a predator of phytophagous and predacious mites in a Dutch orchard

Rate of development and reproduction of Orius vicinus was measured on different sorts of animal prey and on Vicia fabae pollen. Several phytophagous and predacious mites proved to be good prey species for the predator, but some small insects, such as Typhlocyba sp. and Aphis pomi were less suitable. Reproduction on a diet of Vicia fabae pollen was distinctly lower than on animal prey.

Protein changes in the haemolymph of Pieris brassicae during the last larval instars and the beginning of the pupal stage

Abstract Disk electrophoresis in polyacrylamide gels was used to study protein changes in the haemolymph of Pieris brassicae during the last larval instars and the beginning of the pupal stage. A number of high molecular weight proteins were found to increase in concentration during the development, followed by a decline to begin at the pharate pupal stage and to continue after the larval-pupal ecdysis. These proteins are mainly glyco- and lipoproteins. The presence of the following enzymes could be shown: esterases, leucinaminopeptidase, and alkaline and acidic phosphates.

House-dust mite (Pyroglyphidae) populations in mattresses, and their control by electric blankets.

A reduction in house-dust-mite populations of 19–84% in beds in regular use could be achieved by heating the mattresses with electric blankets, when the beds were not being slept on. The effect of the heating treatment on the temperature and relative humidity inside the mattress is discussed. Housedust mites in the heated portions of the mattress migrated deeper inside the mattress to a depth of 3.5–5.0 cm. Evidence was also found that house-dust mites in non-heated mattresses do not only live near the surface, but that they are also present deep inside the mattress.

Cold-hardiness in the predatory mite Amblyseius potentillae ( Acari: Phytoseiidae )

Cold-hardiness was studied in the predatory miteAmblyseius potentillae (Garman) by determining the mortality after exposure to −5°C. Predators reared under diapause-inducing conditions were more cold-resistant than mites that had been kept under long-day conditions. An acclimatization period at 4°C prior to exposure to sub-zero temperatures had a positive effect on the cold-hardiness of the predator, and was remarkable in diapausing mites.Lower temperatures during diapause induction had a positive effect on cold resistance in this predator; mites in which diapause was induced at 15°C were more cold-resistant than mites that had been subjected to short-day conditions at 18 and 20°C.A day/night temperature rhythm did not increase the cold-hardiness of the mite when grown under long-day conditions. Such a rhythm did increase the cold-hardiness of the diapausing predator when given a short acclimatization period, but this effect disappeared after longer acclimatization periods.

Standardization of Bacillus thuringiensis preparations: A new bioassay method with Pieris brassicae as test insect

Abstract A new bioassay method for Bacillus thuringiensis preparations is described with Pieris brassicae as the test insect. Although considerable differences were found in LC 50 values of replicates, reproducible results were obtained when potency ratios were considered. Results were tested statistically and compared with data reported in the literature by others.

Preliminary notes on the pathogenicity of some Erynia strains (Mycophyta, Entomophthoraceae) towards larvae of Pieris brassicae

Fifteen different isolates of Erynia (Zoophthora) sp. were tested with respect to their pathogenicity towards larvae of Pieris brassicae. Only 6 isolates were able to provoke infection in the larvae. The potential of Erynia radicans as a mycoinsecticide is discussed.