Pesticide Science (1997) 49, 252-258

Ralf Nauen and Alfred Elbert (1997)
Apparent tolerance of a field-collected strain of Myzus nicotianae to imidacloprid due to strong antifeeding responses
Pesticide Science 49 (3), 252-258
Abstract: A French strain of the tobacco aphid Myzus nicotianae Blackman (Homoptera: Aphididae), strain FR, showed high tolerance to imidacloprid in short-term (48-h) oral ingestion bioassays when compared to a susceptible reference strain of Myzus persicae, strain NS. The resulting tolerance factors were >50. Measures of the contact activity of imidacloprid by the FAO dip method failed to detect these high factors of tolerance. The tolerance factor was in general <10 when using the dip method. The resulting difference between tolerance factors could be attributed to a behavioural component to fitness between strain FR and strain NS as further experiments revealed. When measuring the effect of systemically applied imidacloprid on honeydew excretion, a 50% reduction occurred in both strain FR and strain NS at nearly the same concentration of imidacloprid, providing evidence for a similar antifeedant response in both strains. Starvation experiments revealed that the French strain was able to survive approximately 24 h longer than a reference laboratory strain of M. persicae. This result coincided with the fact that systemically applied imidacloprid showed the same aphicidal potential against strain FR after three days as against strain NS after two days, i.e. 24 h later. After rearing in the laboratory for six months the French strain of M. nicotianae lost its hardiness and also its apparent ability to tolerate imidacloprid. However, strain FR was a heterogeneous field strain and it is possible that a susceptible variant out-reproduced a more hardy variant.
These findings indicate that the type of bioassay is very important when assessing aphid populations for resistance against the chloronicotinyl insecticide imidacloprid, because of its distinct mode of action. It is obvious that an aphid dip test, i.e. FAO dip test, produces more reliable results than the different kinds of short-term oral ingestion bioassays, because of the reversible behavioural changes induced by imidacloprid after oral uptake. Thus a short-term oral ingestion bioassay (<48 h) is not recommended for precise detection of possible resistance of Myzus sp. to imidacloprid, although this mode of uptake for imidacloprid might be sometimes more realistic in terms of field behaviour. The ideal test to generate most accurate data would be a slightly longer (72-h) feeding bioassay, perhaps used in conjunction with a dip test. The possible influence of the results on resistance monitoring is discussed.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Ralf Nauen

Research topic(s) for pests/diseases/weeds:
control - general
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Myzus nicotianae		France