The effect of fenvalerate on the oviposition response of white butterfly: A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Horticultural Science (Honours) in the University of Canterbury

Abstract

The effect of 1/100 field rate, field rate and 10 x fieldrate of fenvalerate on the oviposition response of white butterfly (Artogeia rapae L.) was evaluated in a series of laboratory and field experiments. In the laboratory experiments white butterfly females were caught in the field and placed into an experimental cage. A leaf disc holder with 50 mm broccoli leaf discs (three treated and three untreated discs) was then placed for 30 minutes into the cage and the landing behaviour of the insects observed. At the end of the experiment the number of white butterfly eggs laid was counted. In the field experiments, plots consisting of four cabbage plants placed 500 mm apart to form a square (two treated with field rate fenvalerate and two control plants), were set out for two consecutive days. White butterfly eggs laid were counted at the end of the experiment and landing behaviour of the insects observed during two observation periods. Gravid white butterfly females were able to distinguish between host and non-host leaf discs under laboratory conditions. The mean number of white butterfly eggs laid on broccoli leaf discs treated with 1/100 field rate fenvalerate was 50% greater, treated with field rate fenvalerate 30% smaller and treated with 10 x field rate fenvalerate 10% greater, when compared with control leaf discs. However these differences were not statistically significant. The overall landing and touch-down patterns showed no recognizable pattern, but usually showed the same differences between treated and control discs as observed for the egg numbers. In the field no significant difference in mean egg numbers per plant were found between cabbage plants treated with field rate fenvalerate and control plants. In the first experiment treated plants received 20% more, in the second experiment 20% less white butterfly eggs. While in the latter experiment observed landings were of similar magnitude, twice as many landings per observation period on treated plants were observed in the first experiment. As results may have been due to random variation caused by materials and methods used in the laboratory and field experiments more experimental work is needed to investigate the effect of fenvalerate on white butterfly oviposition response.