Reet Karise

Gas exchange patterns of bumble bee foragers before and after exposing to lowered temperature

The gas exchange patterns are known to vary between insect species, individuals and even intra-individually. Using volumetric-manometric and flow-through respirometry combined with IR-actography we studied how periods of low temperature affect the respiratory patterns of bumble bee Bombus terrestris foragers. We have shown, in this study, that there is a change in the respiratory patterns of individual B. terrestris foragers after exposing to low temperatures. The bumble bees seemed to become more inactive. The different respiratory patterns appeared in succession and the transition from one pattern to another was associated with the change from an active to a resting state. Typical patterns after exposition to low temperature were discontinuous gas exchange cycles (DGCs).

Factors affecting cold hardiness in the small striped flea beetle, Phyllotreta undulata

The striped flea beetle, Phyllotreta undulata Kutschera (Coleoptera: Chrysomelidae), is a pest of cruciferous crops. It overwinters as an adult. During winter in northern European countries, such as Estonia, it is subject to sometimes severe temperatures that may fluctuate daily, over the season, and between seasons. The objective of this study was to investigate factors that affect its cold hardiness. In a series of five experiments, the effects of food plant, starvation, and acclimatization on the beetles’ ability to supercool and survive exposure to sub‐zero temperatures was investigated. The supercooling points (SCP) of overwintered beetles field‐collected from white mustard and Indian mustard differed from those caught from white cabbage and oilseed rape, but these differences disappeared after a 4‐day period of starvation at room temperature, indicating that gut content probably influences the potential to supercool. The duration and temperature of acclimation affected SCP in overwintered beetles. The decrease in SCP was more rapid at 22 °C than at 0 °C, probably because of faster dehydration and gut evacuation at the higher temperature. Acclimation at 0 °C for a week increased the ability of overwintered beetles to survive sub‐zero temperatures, lowering both SCP and lower lethal temperature (LLT50). Some pre‐freeze mortality occurred; SCP and LLT50 were correlated but the latter was a constant 3 °C higher than the former. The SCP of field‐collected pre‐winter beetles decreased gradually during the autumn. It also decreased when field‐collected pre‐winter beetles were acclimated at 0 °C in the laboratory, attaining its lowest level after 18 days. Phyllotreta undulata is well‐adapted to unstable and sometimes severe winter conditions; its high potential to supercool enhances its cold hardiness and ability to survive short periods at sub‐zero temperatures although it cannot survive freezing of its body fluids.

Sublethal effects of kaolin and the biopesticides Prestop-Mix and BotaniGard on metabolic rate, water loss and longevity in bumble bees (Bombus terrestris)

Kaolin is an inert material with a broad range of applications, e.g. as an insecticide and as a filling substance in the formulation of biopesticides. Hence, bees that dispense biopesticides to the field in the context of entomovectoring are exposed to elevated risks because of side-effects of those products. Here, we investigated with use of bumble bee workers of Bombus terrestris L. the lethal and sublethal effects of (i) pure kaolin, (ii) the biofungicide Prestop-Mix containing the parasitic fungus Gliocladium catenulatum and kaolin and (iii) the bioinsecticide BotaniGard containing the entomopathogenic fungus Beauveria bassiana and compared with wheat flour powder that we considered safe for bumble bees. As the most important result, treatment with kaolin increased the cuticular water loss and reduced the survival of treated bumble bees, while Prestop-Mix had no negative effect on longevity. BotaniGard caused mortality in the bumble bees because of the entomopathogenic spores it contained. In conclusion, our data indicated that substances used as ‘inert materials’ and in biocontrol agents which are used in IPM and organic farming systems may bring higher risks to bumble bees used in entomovector technology.

Effects of Fastac 50 EC on bumble bee Bombus terrestris L. respiration: DGE disappearance does not lead to increasing water loss.

Sublethal effects of pesticides in insects can be observed through physiological changes, which are commonly estimated by metabolic rate and respiratory patterns, more precisely by the patterns of discontinuous gas-exchange (DGE) cycles. The aim of the present research was to study the effect of some low concentrations of Fastac 50 EC on the cycles of CO(2) release and respiratory water loss rates (WLR) in bumble bee Bombus terrestris L. foragers. Bumble bees were dipped into 0.004% and 0.002% Fastac 50 EC solution. Flow-through respirometry was used to record the respiration and WLR 3h before and after the treatment. The respirometry was combined with infrared actography to enable simultaneous recording of abdominal movements. Our results show that Fastac 50 EC has an after-effect on bumble bee respiratory rhythms and muscle activity but does not affect WLR. Treatment with 0.004% Fastac 50 EC solution resulted in disappearance of the respiration cycles; also the lifespan of treated bumble bees was significantly shorter. Treatment with 0.002% Fastac 50 EC solution had no significant effect on respiration patterns or longevity. We found no evidence for the DGE cycles functioning as a water saving mechanism.

Oilseed Rape, Bees and Integrated Pest Management

As a major mass-flowering crop producing an abundance of nectar and pollen, oilseed rape is very attractive to honey bees, bumblebees and solitary bees. It provides a food resource of considerable value in sustaining bee populations in agroecosystems at a time when bees are in decline. Although the flowers are self-fertile, they are entomophilous, and pollination studies, both in the glasshouse and in the field, suggest that bee foraging activities on the crop have many beneficial effects for the grower, including improving both the quantity and quality of the seed produced. However, bees foraging on the crop are vulnerable to the effects of insecticides, mostly pyrethroids applied to the crop, particularly when these are applied during flowering to control inflorescence pests. Effects may be lethal or sub-lethal; the latter have been little studied but there is growing evidence that insecticides affect many aspects of bee behaviour and physiology, such as division of labour, foraging and orientation, reproduction and respiration. Husbandry practices on the crop must therefore seek to minimise the use of insecticides on the crop, particularly during flowering, in order to sustain and not diminish bee populations foraging on the crop. Bees may even have a role in integrated pest management strategies incorporating biocontrol through their capacity to vector entomopathogenic fungal spores to the flowering canopy of oilseed rape to kill inflorescence pests.

Recent insights into sublethal effects of pesticides on insect respiratory physiology

Determination of the sublethal effects of pesticides on insects is a challenging topic because of the vast number of different possible end points. Sublethal effects can manifest themselves through changes in motor activity, behavior, or, in the case of social insects, learn- ing ability. These are still the outcomes of physiological changes. As autonomic processes like respiration assure the normal functioning of any organism, the estimation of disturbances of these processes can give valuable data for toxicology researchers. This review reports a vari- ety of effects of pesticides on insect respiratory patterns, metabolic rate, and water loss rate. Although the tested pesticides and target subjects belong to very different groups, the results of the reviewed studies indicate several common effects. We conclude that the study of the pesticide effects on insect respiratory physiology has potential for further development as a methodology for measurement of basic physiological changes as it allows measurement of the intact living insect, the result is obtained rapidly, and several parameters can be measured simultaneously. At the same time, the method has its shortcomings: the equipment is expensive and complicated, the results can be affected by the experimental conditions, and as yet there are no standardized end points for data comparison.

Factors affecting development and overwintering of second generation Colorado Potato Beetle (Coleoptera: Chrysomelidae) in Estonia in 2010

We have established for the first time that Colorado potato beetle (CPB) (Leptinotarsa decemlineata Say) (Coleoptera: Chrysomelidae) produced a distinct second generation in 2010 in Estonia. This species has a history, in Estonia, of less than 50 years. Due to their great ability to adapt to variable environmental conditions, the beetles spread very quickly throughout the country and established a permanent population in the 1980s. Before 2010, CPB has been predominantly univoltine. The occurrence of the second generation was the result of rare coincidence of extremely favourable weather as the cumulative degree days (DD) of 927 exceeded the sum needed for two full generations. Constantly high temperatures from the beginning of May caused the formation of summer generation adults already by the end of July and the long day photoperiod, as well the availability of fresh food, kept the beetles in reproductive mode preventing the onset of diapause. Summer beetles continued to oviposit up to the second half of September, but a large proportion of the second generation was eliminated from the population in the pre-adult or adult stages as they failed to end their development in the favourable period. Successful overwintering with about 50% survivors occurred only in association with completed development which was restricted to August and the beginning of September. An abundant second generation has potential to reduce primarily the yield of late potato cultivars. However, the unpredictable weather conditions in Estonia does not allow exact prediction of the appearance of a second generation.

Synergistic interactions between a variety of insecticides and an ergosterol biosynthesis inhibitor fungicide in dietary exposures of bumble bees (Bombus terrestris L.): Synergistic interactions between a variety of insecticides and fungicide

BACKGROUND In recent years, concern has been raised over honey bee colony losses, and also among wild bees there is evidence for extinctions and range contractions in Europe and North America. Pesticides have been proposed as a potential cause of this decline. Bees are exposed simultaneously to a variety of agrochemicals, which may cause synergistically detrimental impacts, which are incompletely understood. We investigated the toxicity of the fungicide imazalil in mixture with four common insecticides: fipronil (phenylpyrazoid), cypermethrin (pyrethroid), thiamethoxam, and imidacloprid (neonicotinoids). Ergosterol biosynthesis inhibitor (EBI) fungicides like imazalil can inhibit P450 detoxification systems in insects and therefore fungicide - insecticide co-occurrence might produce synergistic toxicity in bees. We assessed the impact of dietary fungicide - insecticide mixtures on the mortality and feeding rates of laboratory bumble bees (Bombus terrestris L.). RESULTS Regarding mortality, imazalil synergised the toxicity of fipronil, cypermethrin and thiamethoxam, but not imidacloprid. We found no synergistic effects on feeding rates. CONCLUSION Our findings suggest that P450-based detoxification processes are differentially important in mitigating the toxicity of certain insecticides, even those of the same chemical class. Our evidence that cocktail effects can arise in bumble bees should extend concern about the potential impacts of agrochemical mixtures to include wild bee species in farmland.

Reliability of the entomovector technology using Prestop-Mix and Bombus terrestris L. as a fungal disease biocontrol method in open field

Botrytis cinerea Pers.:Fr. is a major plant pathogen, and a new approach is needed for its control in strawberry to minimise the increasing use of synthetic fungicides. The biofungicide Prestop-Mix, which contains Gliocladium catenulatum, is effective against Botrytis infections; however, the need for frequent applications increases the costs for farmers. Here, we demonstrate that bumble bees, Bombus terrestris L., effectively disseminate the preparation onto flowers in open field conditions. Over the course of three years, we found a highly significant decrease in the rate of Botrytis infection. Pathogen control was achieved with relatively low numbers of G. catenulatum spores per flower, even using flowers that are not highly attractive to bumble bees. An even distribution of spores was detected up to 100 m from the hives, either due to primary inoculation by bumble bees or secondary distribution by other flower visitors such as honey bees and solitary bees. We showed that the application of a biocontrol agent by bumble bees is reliable for the use of environmentally friendly pest control strategies in northern climatic conditions. This low cost technology is especially relevant for organic farming. This study provides valuable information for introducing this method into practice in open strawberry fields.

Variability in metabolic rate and gas exchange patterns of the Colorado potato beetle of winter and prolonged diapauses: Gas exchange patterns of Colorado potato beetle

We compare standard metabolic rate (VCO2) and gas exchange patterns in the Colorado potato beetle (Leptinotarsa decemlineata Say) in winter diapause (i.e. lasting only one overwintering period) with those of beetles in prolonged diapause (i.e. diapause lasting 2 or 3 years). The length of diapause is estimated by the behaviour of the beetles: burrowing into soil as a sign of the beginning of diapause and emergence from the soil as the ending of diapause. Measurement with a flow‐through carbon dioxide (CO2) infrared gas analyzer reveals that most beetles in winter or prolonged diapause display distinct discontinuous gas exchange cycles at 23 °C. Beetles with cyclic gas exchange and continuous breathing do not survive the winter. Beetles in prolonged diapause are characterized by a three‐ to five‐fold lower standard metabolic rates, longer discontinuous gas exchange periods and shorter CO2 releases (open phase) than those in winter diapause.