Influence of pollen feeding and physiological condition on pesticide sensitivity of the honey bee Apis mellifera carnica.

In two consecutive years heavy bee mortality at end April/early May followed the use of pesticides classed as harmless for bees along road verges. It was thought that old weak winter bees had succumbed to a preparation otherwise innocuous. Extensive tests to reveal any links between the bees' physiological condition and pesticide sensitivity involved 6 hormone herbicides, 11 fungicides and 2 insecticides, all approved harmless for bees and functioning on them wholly or mainly as stomach poisons. As a rule bee sensitivity was measured as LD 50 per os, in smaller tests as percentage mortality. Amount and quality of pollen ingested in the first days of life affected the pesticide sensitivity of young and older bees. Bees fed adequate high quality pollen are less sensitive than counterparts fed inadequate or inferior pollen or pollen substitute; such differences persisted if the LD 50 was calculated for the same body weight. Pesticides containing manganese are an exception. To these, bees fed inadequate pollen are no more or even less sensitive than comparable well-fed bees. Pesticide sensitivity decreases generally from early to late summer. Quality of pollen available for larvae has no effect on poison sensitivity of imagines. Food supply conditions however exert a clear influence: tested with the same pesticides, hive bees from colonies having had a rich early food supply, and young bees bred then, are less sensitive than their counterparts having had moderate or no early food supply. Poison sensitivity of summer bees increases with age; most sensitive are old winter bees which had practiced broodcare in early spring.Inadequate pollen intake can be regarded as causing protein deficiency. Investigation of this in mammals and man indicate that the higher poison sensitivity in bees results from inhibition of the enzymatic decomposition of pesticides. For practical bee protection it is important that all organic fungicides tested are effectively harmless. Hormone hebicides can be ranked as practically harmless even for bees inadequately protein-fed, as long as the approved concentrations are observed. Our tests raised doubts however about the registration as harmless for bees of insecticides based on Endosulfan and Phosalon. Of interest in practice and for the official testing of pesticides are also the high pesticide sensitivity of old winter bees, the decrease in sensitivity of bees on a stable feed from early to late summer, and the sensitivity-reducing influence of pollen-rich food supply promoting development.It is important ecologically that pollens of different plant species vary in nutrient quality for the honey bee: there are perfectly worthless (conifers), poor-to-medium, and highly effective pollen types. As shown in this paper, these differences are relevant not only for the development of the physiological condition and breeding potential of the bee, but also for pesticide sensitivity. That bees gather worthless and poor-quality, sometimes even poisonous, pollen (some Ranunculus sp.) is evidently due to the phagostimulant present in all pollen types.