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[SANET-MG] Honey bees may succumb to friendly fire?



1 May 2007
Prof. Joe Cummins
Parasitic fungi and pesticides interact synergistically to kill insect pests: Honey bees may succumb to friendly fire? Honey bees are facing an unparalleled threat from something in the environment which is causing them to leave their hives but never return. The condition is called Colony Collapse Disorder (CCD). A number of ideas have been put forward to explain the catastrophe (1). The leading areas of concern are systemic insecticides ( the neonicotinoid systemic pesticides used worldwide to treat seeds and crops) including the genetically modified (GM) crops (1,2), parasitic fungi (3) and radiation associated with mobile phones (4). These environmental threats all are believed to have similar effects on the honey bees. Parasitic fungi are used extensively as entomopathogenic biocontrol organisms. Fungal spores are used to deliver the parasites in sprays or baits. It has been observed that the parasites frequently interact synergistically with neonicotinoid pesticides, particularly the insecticide imidacloprid which delivered at a sublethal level t in a liquid suspension of parasite spores. Significant enhancement to the insecticidal activity of the fungal spores are often observed. The spores of the insect killing fungus Beauveria bassinia was used to treat the brown leafhopper pest of rice , when accompanied by a sublethal dose of imidacloprid the formulations acted earlier and greater activity than the spores of the fungus alone (5). The sweet potato whitefly was controlled using the fungus Lecanicillium muscarium combined with sublethal levels of imidacloprid gave satisfactory control of the fly and merited inclusion in integrated control programs (6). Beauveria bassinia spores combined with imidacloprid at a level one tenth the lethal dose was found to significantly enhance control of the leaf cutting ant(7) Termites were controlled by imidacloprid at sublethal levels enhancing the fungal parasite Metarhizium anisopliae (8). The point of this discussion is to show that the presence of neonicotinoid insecticides in at sublethal levels causes enhanced insect killing by the fungal parasites. The neonicotinoid insecticides used to treat seeds are systematic and accumulate in plant parts including flowers .The presence of the insecticides at sub lethal level seems to interfere with the insect’s immune system leading to susceptibility to fungal pathogens. The parasitic fungus, Nosema ceranea, a single celled parasite was found in CCD affected bee hives from around the USA (3). Nosema locustae has been a commercial biocontrol fungus to control locusts and grasshoppers. An integrated pest management strategy, with an emphasis on the use of Metarhizium an ascosporic fungus , that incorporates rational use of chemical pesticides with biological options such as the microsporidian Nosema locustae and the hymenopteran egg parasitoids Scelio spp., has become a realistic option. (9). Nosema bombycis has been a major pest of the silkworm but it has been used as a to control Diamondback moth. Another microporidian , Vairimorpha sp.,isolated from the Diamondback moth in Malaysia caused 100% mortality when applied to moth larvae at 1500 spores per larva (10). Nosema pyrausta infects the European corn borer and can be used in biocontrol of the pest. Purified Bacillus thuringiensis Cry1Ab toxin was fed to Nosema infected and uninfected borer larvae. Nosema infection reduced the lethal dose of Cry!Ab toxin to one third the lethal dose of the uninfected larvae (11). The Bacillus thuringiensis kurstaki (Dipel) formulations were used to treat Nosema pyrausta infected and uninfected corn borer larvae. The infected larvae had a lethal dose 45 times lower than the uninfected larvae (12). I am not suggesting that biocontrol agents pose a threat to the honey bee, rather, I am pointing out that there is a good indication that exposure to sublethal levels of systemic insecticides used in seed treatment of both conventional and GM crops and in widespread soil and foliar applications can effect beneficial insects by reducing their immunity to parasitic fungi. Regulators have allowed extensive deployment of systemic insecticides for seed treatment and they have allowed extensive use of foliar sprays of the systemic insecticides on a wide array of food and feed crops. The impact of such pesticides on honey bees has been evaluated using measurements of lethal dose alone , ignoring the clear evidence that sublethal doses of the insecticides act synergistically with fungal parasites of the insects that are beneficial along with the insect pests. The honey bees may b e falling victim to “friendly fire” directed to exterminating insect pests. Unfortunately, regulators around the world have dealt with decline of honey bees through tunnel vision, ignoring well established pesticide-fungal parasite interactions. Such regulators must be awakened from their nap.
References
1.Ho,M-W and Cummins,J. Mystery of disappearing bees Science in Society 2007 34 in press
2.Cummins,J. Requiem forthe honey bee Science in Society 2007 in press
3.Cummins,J. A parasitic fungus Nosema ceranea and honey bee decline in press 4. Ho,M-W Mobile phones and vanishing bees Science in Society 2007 , 34 in press 5. Feng MG and Pu XY. Time-concentration-mortality modeling of the synergistic interaction of Beauveria bassiana and imidacloprid against Nilaparvata lugens. Pest Manag Sci. 2005 Apr;61(4):363-70. 6. Cuthbertson AG, Walters KF and Deppe C. Compatibility of the entomopathogenic fungus Lecanicillium muscarium and insecticides for eradication of sweetpotato whitefly, Bemisia tabaci. Mycopathologia. 2005 Aug;160(1):35-41. 7. Santos AV, de Oliveira BL and Samuels RI. Selection of entomopathogenic fungi for use in combination with sub-lethal doses of imidacloprid: perspectives for the control of the leaf-cutting ant Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae). Mycopathologia. 2007 Apr;163(4):233-40. 8. R Ramakrishnan, DR Suiter, CH Nakatsu, RA Humber and Bennett,G. Imidacloprid-Enhanced Reticulitermes flavipes (Isoptera: Rhinotermitidae) Susceptibility to the Entomopathogen Metarhizium anisopliae J. Econ. Entomol, 1999,92(5): 1125-32 9. Lomer CJ, Bateman RP, Johnson DL, Langewald J and Thomas M. Biological control of locusts and grasshoppers. Annu Rev Entomol. 2001;46:667-702. 10. Sarfraz, M. Keddie, A and Dosdall, L. Biological control of the diamondback moth, Plutella xylostella : A review Biocontrol Science and Technology 2005, 15,763-89 11. Reardon BJ, Hellmich RL, Sumerford DV and Lewis LC. Growth, development, and survival of Nosema pyrausta-infected European corn borers (Lepidoptera: Crambidae) reared on meridic diet and Cry1Ab. J Econ Entomol. 2004 Aug;97(4):1198-201. 12. Pierce CM, Solter LF and Weinzierl RA. Interactions between Nosema pyrausta (Microsporidia: Nosematidae) and Bacillus thuringiensis subsp. kurstaki in the European corn borer (Lepidoptera: Pyralidae). J Econ Entomol. 2001 Dec;94(6):1361-8.

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