RT Dissertation/Thesis
T1 The role of pollen as alternative food for predatory mites (Acari: Phytoseiidae)
A1 Schreiber,Irina
WP 2018/12/05
AB Predatory mites of the family Phytoseiidae (order Acari) are important biological control agents of various greenhouse pests. Their successful establishment in greenhouses depends on abiotic and biotic factors, and on different adaptation levels of the different mite species, which must be considered before practical implementation.
In this study, the suitability and effect of pollen as alternative food was assessed for the predato-ry mites A. swirskii, A. limonicus, and A. cucumeris (Acari, Phytoseiidae). Besides lifetable and demographic parameters, body weight and size was included into the descriptive parameters, which has not been done before to obtain more detailed information on pollen quality for these mite species.
In the first study (Goleva and Zebitz 2013), the suitability of pollen of 21 plant species as alternative food for A. swirskii was tested. Preimaginal mortality and developmental time have been assessed, followed by a life-table analysis of the emerged adults and a calculation of demographic parameters. Amblyseius swirskii was able to feed on 18 pollens, but the nutritional properties of the pollen differently affected mite performance. Pollen of Lilium martagon and Hippeastrum sp. were found to be toxic for the mites, probably due to secondary plant compounds in this pollen. Amblyseius swirskii was absolutely not adapted to feed on Hibiscus syriacus because of the external morphology of pollen grains, leading also to 100 % preimaginal mortality. The best pollen resulting in superior mite performance in all parameters tested were: Aesculus hippocastanum, Crocus vernus, Echinocereus sp. and Paulownia tomentosa. No or low mortality was observed when mites fed on other pollen tested. Developmental time, adult longevity, and reproduction parameters, were significantly affected, probably because of differences in pollen nutrient or non-toxic secondary compound composition. Commercial bee pollen was of very poor quality for the mites leading to low egg production, which excludes this pollen for practical use. Pollen of Helianthus annuus, Corylus avellana and a Poaceae-mix were of inferior quality, causing high mortality rates, low egg production and short adult longevity. For practical implementation in greenhouses, pollen of Ricinus communis, Zea mays, A. hippocastanum and Betula pendula pollen appeared suitable to improve predatory mite performance, either provided by banker plants or in form of dispersible pollen.
The objective of the second study (Ranabhat et al. 2014) was to assess the suitability of seven pollen (castor bean, tulip, apple, Christmas cactus, horse-chestnut, maize, and birch) for Neoseiulus cucumeris (Acari: Phytoseiidae), and to scrutinize potential effects of these pollen on reproduction and life history parameters of this mite. Neoseiulus cucumeris accepted six pollen sources as alternative food, pollen of castor bean plants, however, caused 100 % mortality. Highest fecundity was observed when feeding on pollen of tulip and horse chestnut, resulting in the shortest preimaginal development compared with all pollen tested. Pollen of birch, tulip, maize, and apple had a positive effect on longevity, whereas pollen of horse-chestnut and Christmas cactus was significantly inferior.
Our study suggests that birch, tulip, horse-chestnut, apple, and maize pollen may serve as alter-native food in the field, and birch and maize pollen have a good potential in practical use as banker plants or dusts in the greenhouse to guarantee mite establishment in periods of prey scar-city.
The aim of the third study (Goleva et al. 2014) was to investigate the role of pollen of differing quality (tested previously in first study (Goleva and Zebitz 2013) on size and weight of A. swirskii. These parameters were considered from the physical aspect of predator-prey relations because predatory mites are not able to conquer prey individuals bigger than themselves and any deviation from normal size may negatively affect predation success. Biomass and body size of freshly emerged, 1, 3, and 30 days old adult A. swirskii continuously reared on pollen of B. pendula, H. annuus, P. tomentosa, and Zea mays revealed, regardless of pollen source, that females were bigger than males. Both parameters weight and size were affected by pollen tested. Females fed on pollen of P. tomentosa and Z. mays were significantly bigger than on B. pendula or H. annuus pollen. Increase of female biomass was observed until the adult age of 3 days, remaining constant or slightly decreased until the age of 30 days. This can be explained by particularly high nutritional requirements of females for egg production especially in the beginning of their repro-duction period. Males also reached their weight maximum at day 3 of adult life, then decreasing until day 30. Congruent with biomass, adult body length and width differed significantly depending on sex and age showing females bigger than males and 30 day old adults bigger than 1 day old adults irrespective of the pollen fed. While sunflower pollen was of poor quality for A. swirskii, causing small size and low weight of both sexes, pollen of P. tomentosa was significantly superior in both parameters. No reasonable correlation was found between body length and width, but body weight was significantly correlated with body length in females whereas there was no correlation at all in males.
In a fourth study (Goleva et al. 2015), adult body weight of the generalist mites A. swirskii, A. limonicus, and N. cucumeris reared on 22, 12, and 6 pollen species, respectively, was assessed. In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs.In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs. In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs.In addition, A. swirskii and A. limonicus were reared on codling moth (Cydia pomonella) eggs. In all mite species, female body weight was higher than that of males.Nutritional quality of pollen was neither consistent among the mite species nor among sex, revealing superior quality of Quercus macranthera pollen for females of A. swirskii and T. gesneriana pollen for males, Alnus incana pollen for females of A. limonicus and Ae. Hippocastanum pollen for males, and Ae. Hippocastanum pollen for both sexes of N. cucumeris. 
Pollen affected predatory mite species in our studies in various ways. Besides lifetable parame-ters, pollen also affected adult weight and size of predatory mites and these parameters should therefore be considered additionally in future studies to obtain more exhaustive information on nutritional biology and physiology of predatory mites.
The differences in the parameters assessed and the mite species performance may be explained by different adaptations of mite species to pollen compounds. Knowledge in the chemical composition of pollen, however, particularly the nutritive substances, is poor or even lacking. Any correlation of performance parameters with nutrients is more or less theoretical unless the pollen constituents are known. Even then, nutritional physiology of predatory mites and their adaptation to various food sources must be improved and include mite’s enzymatic activity to metabolize secondary plant compounds in pollen. The results presented in this thesis open the door to future research on mite nutritional biology.
K1 Pollen
K1 Raubmilben
PP Hohenheim
PB Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
UL http://opus.uni-hohenheim.de/volltexte/2018/1556