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.

Diseases of mites

Phytoseiid mites under environmental stress

The Coffee Berry Borer (CBB), Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae) has been a serious insect pest of coffee cultivars C. robusta and C. catimor in India since 1991, causing 40-80% coffee bean loss. To combat this important pest, an indigenous entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin was isolated from dead and moribund coffee berry borers from the wild. The fungus was cultured on yeast extractpeptone supplemented liquid medium. The mycelial mat was harvested from 12-day old cultures and lyophilized. A suspension of the most virulent isolate (Bb2) was prepared in sterile water and used as a mycopesticide. The laboratory studies were conducted on coffee berry borers by applying conidial suspensions at a dosage rate of 1 &#50 10 6 conidia ml -1 . Pest mortality with the Bb2 isolate increased from 69.3% to 95.3% with an increase in relative humidity (RH) at 25 &#45 2°C. Field experiments were conducted in a coffee plantation area in the Kodagu district of Karnataka,...

Beauveria bassiana -A Potential Mycopesticide for the Efficient Control of Coffee Berry Borer, Hypothenemus hampei (Ferrari) in India

Publisher Summary This chapter is focuses on the pathological effects of trypanosomatids on insects Because insects are important pests, any parasite of insects, such as the homoxenous trypanosomatids, should be considered as a possible agent for biological control More and more effects of trypanosomes have been recognized in other systems in the past 10 years The effects of trypanosomatid in each system have been grouped into behavioral alterations, disturbances of organ systems, effects on preadult developmental times and mortality rates, effects on adult life span and reproduction rate, and synergistic effects of trypanosomatids and other stressors Although many trypanosomes reach high population densities in the insect host, strong pathological effects are observed in only a few systems Usually, the interaction of trypanosomes and insects seems to be balanced, and no ill effects are obvious However, under natural conditions, insects are often exposed to adverse conditions—factors that are rarely considered in laboratory studies––and the parasite might then act synergistically with other stressors Theoretical models indicate that synergistic action with other stressors might be important in the regulation of the host population Assuming that all susceptible individuals react sensitively, subpathogenic trypanosomatids also provide a selection pressure on social insects to maintain genetic variability

The effects of trypanosomatids on insects.

Effect of several stress factors on the susceptibility of the predatory insect, Chrysoperla carnea (Neuroptera: Chrysopidae), to the fungal pathogen Beauveria bassiana

Effect of several stress factors on the susceptibility of the predatory mite, Metaseiulus occidentalis (Acari: Phytoseiidae), to the weak bacterial pathogen Serratia marcescens

David Sewall

Papers

Effect of several stress factors on the susceptibility of the predatory mite, Metaseiulus occidentalis (Acari: Phytoseiidae), to the weak bacterial pathogen Serratia marcescens