The efficient planning of a Petersen‐type mark and recapture experiment requires some knowledge of the order of magnitude of the population size N. Sample sizes M and C of the mark and recapture samples, respectively, may then be ascertained on the basis of a guessed value of N to achieve any desired degree of accuracy with any specified degree of confidence. Restrictions on the sample sizes M and C are that MC must exceed 4 times the guessed value of N, and the total costs of M and C must be equal. Graphs and formulas are given defining sample size to attain preassigned levels of accuracy and precision of population estimation. A method of choosing sample sizes such that experimental costs are minimized is described.

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Allylglucosinolate, found in many cruciferous plants, is acutely toxic to Papilio polyxenes larvae, which do not normally attack crucifers. By contrast, larval growth of Pieris rapae, a crucifer specialist, is not affected even by artificially high concentrations of allylglucosinolate. Larval growth of Spodoptera eridania, a generalist feeder, is inhibited by high but not by low concentrations of the compound.

A•T•CTThe assumptions necessary to obtain a valid estimate of survival rate from a single catch curve are discussed. An example of the best estimate of survival rate and its variance is worked out for the case that age is known exactly for the entire sample. A test for validity of the model is illustrated. Methods of estimating the survival rate are also given when some age groups are combined, when an age-length key is used, and when only a segment of the catch curve is usable. A table is provided to facilitate the estimation in this last case.

Statistical methods for estimating and comparing constant survival rates are developed here for sampling designs in which survival of a subject is checked at irregular intervals. The maximum likelihood estimator is derived and shown to be readily calculated using an iterative procedure that starts with the Mayfield (1975) estimate as a trial value. Sampling distributions of this estimator and of the product of two or more estimates are skewed, and normalizing transformations are provided to facilitate valid confidence interval estimation. The sampling distribution of the difference between two independent estimates is found to be sufficiently normal without transformation to allow valid use of conventional normal theory procedures for testing differences and determining sample size for specified power. Statistical validity under the variable intensity sampling design does require that the duration of intervisit periods vary independently of observer perceptions concerning the survival status of the subject and, in order to achive robustness with respect to the assumption of constant survivorship, sampling intensity must vary independently of any temporal changes in the daily survival rate. Investigators are warned not to return earlier than planned to subjects thought to have died, as this observer behavior may cause serious bias in the survivorship estimate.

Optimal designs of recreational angler surveys may require complemented surveys, in which different contact methods are used to estimate effort and catch. All common methods of estimating catch involve on-site interviews that may either be based on access (complete trip) or roving (incomplete trip) interviews. In roving surveys, anglers to be interviewed on a given day arc intercepted with a probability proportional to the length of their completed fishing trip, whereas in access surveys, anglers arc intercepted as they leave the fishery and are intercepted with the same probability regardless of the length of their completed fishing trip. There are four complemented survey designs which use interviews at access points (mail-access, telephone-access, aerial-access, and roving-access); there are four corresponding designs which use roving interviews (mail-roving, telephone-roving, aerial-roving, and roving-roving). For all of these surveys, total catch is estimated as the product of total effort and catch rate. We show that, when access interviews are used, the appropriate catch rate estimator is the ratio of means estimator (i.e., mean catch from interviews divided by mean effort); whereas when roving interviews are used, the appropriate estimator is the mean of the individual ratios of catch divided by effort for each angler. In the roving method, it is necessary to ignore short trips of less than about 0.5 h duration when calculating the mean of the ratios. This stabili/es the variance of the estimates and does not appear to cause any appreciable bias. A bias occurs in the estimates of catch rate and total catch from roving interviews when anglers are subject to a bag limit. This bias can be substantial if the bag limit is effective in limiting the catch. Recently, Jones et al. (1995) discussed a special

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The larva of the green lacewing Chrysopa slossonae lives in colonies of the wooly alder aphid Prociphilus tesselatus upon which it feeds. It disguises itself as its prey by plucking some of the waxy "wool" from the bodies of the aphids and applying this material to its own back. The investiture protects it from assault by the ants that ordinarily "shepherd" the aphids. Larvae artifically denuded are seized by the ants and removed from the aphid colonies. A larva requires on the average less than 20 minutes to coat itself with wax. A hungry denuded larva gives the coating procedure about the same behavioral priority as feeding.