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The accuracy of visual observations in estimating numbers of tuber flea beetles, Epitrix tuberis Gentner, on young potatoes was determined. Potential sources of observational error examined were as follows: (a) observer competence and experience; (b) time spent observing each plant; (c) time of day; (d) plant height; and (e) weather. Observational accuracy versus tuber flea beetle density on plants followed a linear relationship for both experienced and inexperienced observers. Marked differences between experienced and inexperienced observers generally were reduced after 2 h of sampling experience, but some observers were consistently less accurate at sighting beetles than others. When observing small plants, 5-s observations generally were more accurate at sighting beetles per second of observation than 2-, 8-, or 10-s observations. Under uniform weather conditions, accuracy was the same in the morning as in the afternoon. Observer accuracy was significantly reduced under the combined influences of observer fatigue and wind. The relationship of 5-s-per-plant sampling accuracy to plants between 14 and 56 cm in height was linear; however, a quadratic relationship is suspected for plants over the full range of plant heights (i.e. >1 cm). From these data, total tuber flea beetles per plant estimated by 5-s visual observations per plant would be: TFB = TFB0/EhE0n where TFB0 is the total number of flea beetles observed, n is the total number of plants sampled, Eh is a sampling accuracy constant for the mean plant height sampled, and E0 is the observer accuracy constant calculated as a proportion of the most proficient observer(s).

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