A bait of canned fish poisoned with 0.5 % or 1 % mirex substantially reduced populations of the European wasp, Paravespula germanica (Fab.), in a part-cleared, part-forested resort area in the Marlborough Sounds. In separate baiting regimes, bait was taken for as long as 9 weeks when 0.5% formulation was offered from 5 stations, but when 1 % formulation was offered from 10 and from 15 stations the time was reduced to 5 weeks and 4 weeks respectively. Synthetic and extracted materials tested as baits were unattractive to wasps, but fish baits attractive when fresh could be freeze-dried without loss of acceptability. Marked wasps were caught up to 1200 m from their nests, and in the control programme 64 ppm mirex was recovered from dry brood comb of a defunct nest 700 m from the nearest bait source. The importance to bait control programmes of data on flight distance and foraging habits, and of the winter survival of colonies with prolonged queen production, is discussed. Some observations on reproductive biology are made in an appendix to the paper.
To investigate the possible control of grass grub (Costelytra zealandica (White)) by applying insecticides at the time of adult emergence, the pattern of development of pupae and adults and of the appearance of eggs was determined on four sites in four successive years by soil sampling. Data on primary emergence of beetles were obtained on three of the sites and related to presence of eggs in the soil.Light-trap records showed that beetles were not generally trapped until quite old, and the appearance of numbers of beetles in the traps Vias too late in relation to primary emergence to be of value in timing insecticide treatments.Seventeen insecticides of low residue hazard were examined for contact activity against C. zealandica adults. The best of these were "Dursban", Bayer 77488, and diazinon.Three field trials were conducted using these insecticides, two with ultra-low-volume and one with dilute spraying, each applied to plots within areas of infested pasture. DDT was also included in the highvolume spray trial. Up to four applications, each with rates of use up to I lb per acre, were made. Results, based on ensuing numbers of eggs and larvae in the plots, were all negative.It is suggested that the failure of treatments to exert any effect is associated with the behaviour of adult beetles, especially females, resulting in very limited contact with an insecticide deposit on the pasture surface.Unless ways of increasing this contact can be devised (e.g. by the use of attractants), it is concluded that this approach to control is not likely to be effective.
Susceptibility to insecticides in larvae of Costclytra zealandica (White) has been studied in the laboratory by the topical application of insecticides in solution. Since the onset of mortality, especially that due to DDT, is slow, the loss or retention of the capacity for burrowing in loose soil was adopted as the criterion of effect. Response to DDT occurred over a wide range of dosage when acetone was employed as the solvent; with non-volatile solvents, olive oil or dioctyl phthalate, the range was less and log-dosage pro bit response lines were steeper. Conditions in the post-treatment period affected the slope of the regression line, which was steeper when the larvae were kept in a damp atmosphere than when they were covered with earth. Four main variants in technique are described, and their advantages discussed in relation to the detection and measurement of susceptibility or tolerance to DDT in larval populations, and possible analysis of these into genetically differing fractions.
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