SAMPLING FOR LIRIOMYZA-HUIDOBRENSIS (DIPTERA, AGROMYZIDAE) LARVAE ANDDAMAGE IN CELERY

A sampling plan to estimate population levels of Liriomyza huidobrensi s (Blanchard) larvae and total mining damage was developed for use in celery. Dispersion indices from Taylor's power law were calculated fro m 1992 data obtained from whole plant samples collected from commercia l Fields at two times during the cropping season and utilizing one of three different leafminer management strategies. Analysis of covarianc e indicated that variance-to-mean relationships were consistent among petiole position among plants, pest management strategies, and time of growing season for live L. huidobrensis larvae and total numbers of m ines per petiole. In an attempt to develop a presence-absence sampling plan, an equation was derived to relate the proportion of petioles in fested, P(I), to the mean number of live larvae or the mean number of mines per petiole. However, predicted frequencies of infested petioles derived from this equation were significantly greater than the freque ncies of petioles infested with live larvae or infested with mines obs erved in validation studies. This lack of fit between predicted and ex pected frequencies precludes use of a presence-absence sampling plan t o predict mean densities from the proportion of leaves infested. The r esults From Taylor's dispersion analysis were also used to evaluate a constant precision-level sampling: plan. Validation tests of this samp ling plan indicated that the formula used to calculate critical stopli nes accurately predicted the observed cumulative totals of live larvae or total numbers of mines. Implementation of a sequential sampling pl an for L. huidobrensis larvae with a 0.25 level of precision rind with a possible maximum sample size of 100 petioles (re, compensate for th e prohibitively large sample sizes necessary at low densities) should greatly reduce the amount of labor necessary to achieve accurate estim ates of population densities and to facilitate the use of action thres holds based upon these estimates.