Bijensterfte, oorzaken en gevolgen

Abstract - Concern about the role of pesticides in honey bee decline has highlighted the need to examine the effects of sublethal exposure on bee behaviors. The video-tracking system EthoVisionXT (Noldus Information Technologies) was used to measure the effects of sublethal exposure to tau-fluvalinate and imidacloprid on honey bee locomotion, interactions, and time spent near a food source over a 24-h observation period. Bees were either treated topically with 0.3, 1.5, and 3 mg tau-fluvalinate or exposed to 0.05, 0.5, 5.0, 50, and 500 ppb imidacloprid in a sugar agar cube. Tau-fluvalinate caused a significant reduction in distance moved at all dose levels (p<0.05), as did 50 and 500 ppb imidacloprid (p<0.001). Bees exposed to 50 and 500 ppb spent significantly more time near the food source than control bees ( p<0.05). Interaction time decreased as time in the food zone increased for both chemicals. This study documents that video-tracking of bee behavior can enhance current protocols for measuring the effects of pesticides on honey bees at sublethal levels. It may provide a means of identifying problematic compounds for further testing.

Beliën T, Kellers J, Heylen K, Keulemans W, Billen J, Arckens L, Huybrechts R, Gobin B.

Abstract
Honey bees (Apis mellifera) are the most economically valuable pollinators of fruit crops worldwide. Taking into account bees' contributions to other flowering agricultural crops, about one-third of our total diet comes directly or indirectly from bee-pollinated plants. However, in recent years there increasingly have been worrisome alarm sounds on serious bee mortalities and mysterious disappearance of bees from beehives. Among several environmental factors (e.g. climate and bee pathogens), stress factors arising from agricultural practices can potentially play a role in bee losses.

Als bijen worden blootgesteld aan giftige stoffen maar in te kleine hoeveelheden om er direct aan dood te gaan zijn er vaak toch waarneembare schadelijke effecten te zien. Deze effecten worden sublethale effecten genoemd. Ze worden in de meeste toxiciteitstests over het hoofd gezien en vereisen langdurig veldonderzoek om ze goed in kaart te brengen. Voor imidacloprid is dit gedaan. In de onderstaande tabel staat een overzicht van de gemeten sublethale effecten van imidacloprid op bijen. De linker kolom beschrijft het waargenomen effect. De middelste kolom geeft aan in wat voor soort studies dit effect is gevonden en de rechter kolom geeft aan vanaf welke dosis (hoeveelheid giftige stof per bij) het nadelige effect waargenomen is. De gebruikte afkoringen staan onderaan de tabel verklaard.

Verklaring van de afkortingen em begrippen:
LOEC= Lowest Observed Effect Concentration: De laagste concentratie van een stof in het lichaam (hier van een bij) waarbij al effecten waarneembaar zijn.
NOEC= No Observed Effect Concentration: de hooste concentratie van een stof in het lichaam (hier van een bij) waarbij nog geen (negatieve) effecten worden waargenomen.
ng = nanogram, dat is 0,000000001 gram ofwel een miljardste deel van een gram.
ppb = Parts Per Billion, een maat voor de concentratie van een stof uitgedrukt in het aantal deeltjes van die stof per miljard deeltjes.
Metaboliet = omzettingsproduct. Na opname in de plant wordt imidacloprid langzaam afgebroken. Daarbij ontstaan andere stoffen, de zogenaamde metabolieten van imidacloprid. Sommige van deze metabolieten, zoals het olefin-metaboliet, zijn nog giftiger voor bijen dan imidacloprid zelf. In het veld worden bijen aan een mengsel van imidacloprid en zijn metabolieten blootgesteld.
Chronisch = bij herhaalde toediening gedurende een reeks aaneengesloten dagen (in tegenstelling tot effecten bij eenmalige toediening, die ook wel acute effecten worden genoemd).

Nicolas Desneux, Axel Decourtye, and Jean-Marie Delpuech

Abstract
Traditionally, measurement of the acute toxicity of pesticides to beneficialarthropods has relied largely on the determination of an acute median lethal dose or concentration. However, the estimated lethal dose during acute toxicity tests may only be a partial measure of the deleterious effects. In addition to direct mortality induced by pesticides, their sublethal effects on arthropod physiology and behavior must be considered for a complete analysis of their impact. An increasing number of studies and methods related to the identification and characterization of these effects have been published in the past 15 years. Review of sublethal effects reported in published literature, taking into account recent data, has revealed new insights into the sublethal effects of pesticides including effects on learning performance, behavior, and neurophysiology. We characterize the different types of sublethal effects on beneficial arthropods, focusing mainly on honey bees and natural enemies, and we describe the methods used in these studies. Finally, we discuss the potential for developing experimental approaches that take into account these sublethal effects in integrated pest management and the possibility of integrating their evaluation in pesticide registration procedures.

Laura Bortolotti, Rebecca Montanari, José Marcelino2, Piotr Medrzycki, Stefano Maini,
Claudio Porrini

Abstract
For several years, reports by French and Italian beekeepers have been suggesting a lethal effect of imidacloprid on honey bees; in particular, the molecule has been related to honey bee mortality and decrease of hive populations, affecting the orientation and ability of honey bees to return to the hive.

Axel Decourtye, Eric Lacassie, Minh-Hà Pham-Delègu

Abstract: To establish the sublethal concentrations domain, acute and chronic oral tests were
conducted on caged honeybee workers (Apis mellifera L) using imidacloprid and a metabolite, 5-OHimidacloprid,
under laboratory conditions. The latter showed a 48-h oral LD50 value (153ng per bee)
five times higher than that of imidacloprid (30ng per bee). Chronic feeding tests indicated that the
lowest observed effect concentrations (LOEC) of imidacloprid and of 5-OH-imidacloprid on mortality

Axel Decourtye, James Devillers, Sophie Cluzeau, Mercedes Charreton and Minh-Hà Pham-Delègue

Abstract

E. C. Yang, Y. C. Chuang, Y. L. Chen, and L. H. Chang

Although sublethal dosages of insecticide to nontarget insects have never been an important issue, they are attracting more and more attention lately. It has been demonstrated that low dosages of the neonicotinoid insecticide imidacloprid may affect honey bee, Apis mellifera L., behavior. In this article, the foraging behavior of the honey bee workers was investigated to show the effects of imidacloprid. By measuring the time interval between two visits at the same feeding site, we found that the normal foraging interval of honey bee workers was within 300 s. However, these honey bee workers delayed their return visit for >300 s when they were treated orally with sugar water containing imidacloprid. This time delay in their return visit is concentration-dependent, and the lowest effective concentration was found to be 50 μg/liter. When bees were treated with an imidacloprid concentration higher than 1,200 μg/liter, they showed abnormalities in revisiting the feeding site. Some of them went missing, and some were present again at the feeding site the next day. Returning bees also showed delay in their return trips. Our results demonstrated that sublethal dosages of imidacloprid were able to affect foraging behavior of honey bees.

Figure 4: The ratio of missing bees after feeding on 50% sugar water containing different concentrations of imidacloprid.

Uitleg in het Nederlands: Het plaatje laat zien hoeveel procent van de bijen in het experiment van Yang na het snoepen van suikerwater met imidacloprid hun eigen volk niet meer terug konden vinden, althans, niet meer bij de kast terugkeerden. Hoe meer imidacloprid in het suikerwater werd gedaan (hoe verder naar rechts in het plaatje) hoe hoger het percentage bijen dat de weg naar de korf niet meer terug kon vinden, althans er niet meer aankwam.

Een Canadese Imker heeft zich uitvoerig in de wetenschappelijke discussie over de bijensterfte verdiept. Hij schreef er een artikel over met onder meer dit opmerkelijke feit:

"I would draw your attention to this quote, from the label of Premise 75, a Bayer product with 75% imidacloprid and 25% inert used to kill termites and ants (other social insects like bees): "Premise causes a range of effects in termites, they stop feeding and are unable to maintain their colony. A second effect, exclusive to Premise, is called Premise plus Nature. This product makes termites susceptible to infection by naturally occurring organisms. Either way, the termites die and your home is protected". Exactly, my point, weaken the colony of bees with lethal and sublethal effects and surely disease will set in, and it is crass to use this effect to advertise a product, and then use it to blame beekeepers' problems on diseases."

Bijen en mieren leven beide in een colonie. De toegenomen ziektes bij bijenvolken en de toegenomen blootstelling aan imidacloprid vallen samen in de tijd. Het wordt tijd dat dit mogelijke verband beter onderzocht wordt.