Sex pheromone studies on the grass grub (Costelytra Zealandica (White)) and the common army worm

This thesis describes the identification of a sex pheromone of the grass grub beetle, Costelytra zealandica, and the attempts to use the sex pheromone directly to control grass grub infestations. The partial identification of a sex pheromone of the common armyworm moth, Pseudaletia separata, is also described. The larval stages of the grass grub beetle cause extensive damage to pasture during the autumn-winter period and constitute New Zealand’s major insect pest. Since the banning of DDT, the larvae have been treated by spraying pastures with one of a number of organophosphate insecticides but, in general, these materials have not given adequate control. Attempts have been made, therefore, to develop alternative control procedures and to establish more selective and effective ways of using insecticides. Promising preliminary results have been obtained with other insects in using sex pheromones both as direct and indirect control agents. In the latter respect, a more judicious and effective use of the insecticide has been achieved, by using the properties of specificity and sensitivity of an insect’s sex pheromone to detect, and to estimate, the insect population prior to the application of the insecticide. The female grass grub beetle was shown to contain a sex pheromone which stimulated mating activity in males in the laboratory. Methods were developed to extract the sex pheromone and its properties in functional group tests were consistent with those of a phenolic compound. The active component was isolated by the means of high vacuum distillation onto dry ice followed by gas chromatography. The isolated material was then examined by high resolution mass spectroscopy and found to be phenol. On average each female beetle at the time of mating contained about 1.5μg phenol. Phenol itself not only stimulated mating activity in males in the laboratory but also attracted large numbers of young males in mating flights in the field. Field tests were also carried out with a number of substituted phenols but none of these was active. An electroantennogram was developed to measure the antennal response to phenol and a number of closely related phenolic materials. In all the tests, phenol gave the largest response. A comparison at the antennal level between phenol and a crude female extract indicated phenol was the sole pheromone. Attempts were made to use phenol for grass grub control. The compound is cheap and readily available. Hence its direct use could provide an economically acceptable control method. Interestingly, this was one of the first opportunities to attempt to control an insect population with an unlimited supply of the sex pheromone. There are two ways, in which phenol might be used to prevent effective mating from taking place in the field. Firstly, the attractant properties might be used to out-compete females in the natural population. Secondly, sufficient phenol could be permeated into the atmosphere to possibly confuse the male in its search for the female. Both methods were evaluated in the field with grass grub infestations which ranged from 50 to 220 beetles per m². In the first approach the best attractant sources used were only about ten times more attractive than virgin females and therefore, as they could not compete successfully with the large number of females in the natural population, control was not achieved. In the attempts to use the second approach it was possible to confuse male flight behaviour by releasing 5 grams/hour/hectare (5g/h/ha) of phenol over the trial sites. However, it was not possible to prevent males from locating females even with as much as 110 g/h/ha of phenol released over the trial sites. Presumably, the beetle density of the infestations was such, that males could locate females by sight or simply by chance. Larvae of the common armyworm can cause extensive damage to pastures and crops and although conventional insecticide methods give satisfactory control, the main problems are early detection and estimation of infections. In this respect a knowledge of the sex pheromone used by the female moth should allow insecticides to be used more effectively. The sex pheromone was extracted from the abdominal tips of female armyworm moths using methylene chloride. Functional group tests indicated that the sex stimulatory component was an unsaturated aliphatic acetate. Comparison of the Rf values and retention times of the active component with those of standard compounds on thin layer and gas chromatography (GC) respectively, suggested that a mono-unsaturated hexadecenyl acetate was involved. Of the mono-unsaturated hexadecenyl acetates tested for EAG activity, only cis-11-hexadecenyl acetate induced an intense antennal response. Furthermore, 0.1, 1.0, and 10.0 ng of this compound on glass rods induced strong sex stimulatory activity in males in laboratory behavioural tests. The crude female extract was injected onto a number of different GC columns and several active fractions were collected from each column. This indicated that the female moth probably uses a multiple component pheromone system. The behaviour of one of the sex stimulatory components in the female extract, in all the chemical and concentration steps, was consistent with that of cis-11-hexadecenyl acetate. In an attempt to verify that cis-11-hexadecenyl acetate was a natural pheromone of the common armyworm moth a GC fraction of the crude female extract, eluting at the retention time of cis-11-hexadecenyl acetate, was collected and ozonized. One of the ozonolysis products of cis-11-hexadecenyl acetate is 11-acetoxyundecanal but this was not detected in the ozonized GC fraction, using the technique of mass fragmentography in which a mass spectrometer acts as a specific GC detector. It appears, therefore, that cis-11-hexadecenyl acetate is not present in female armyworm moths. When tested in the field, however, it attracted male moths into traps but was not as effective as virgin females.
Type of thesis
The University of Waikato
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