The pre-oviposition behaviour of Pieris rapae L.

This thesis reports the results of investigations on aspects of the pre-oviposition behaviour of Pieris rapae L. (Lepidoptera: Pieridae) in relation to host plant finding and acceptance. Investigations were carried out into various aspects of the influence of sensory cues on host plant finding including the effect of colour and host plant extracts. The results showed that the number of landings was strongly influenced by colour (P<0.001) and that extracts containing contact stimulants also increased the number of landings (P<0.05).Volatile extracts were also tested in a wind tunnel and the results showed that the extracts increased the number and duration of flights as compared to the solvent controls (P<0.05). However, there was no evidence that the volatile extracts tested acted as attractants. Volatile extracts applied to non-host plants increased the proportion of landings as compared to the controls (P<0.05).The role of different sensory cues (volatile extracts, colour contact stimulants), from three host plants with differing acceptabilities were investigated in order to assess the relative importance of each cue. The results showed that the variety tested had a significant influence on the number of landings and eggs laid. Volatile extracts from the three varieties were prepared and their effect on landing in a choice and no-choice test with model plants was carried out. The volatile extracts significantly increased (P<0.05) the number of landings on the treated plants as compared to the controls.The effect of prior experience was also investigated using three host plants with differing acceptabilities to P. rapae. The results showed that the effect of prior experience (P>0.05) itself was not a significant explanatory variable for the number of eggs laid, however, the host plant variety used was a significant explanatory variable (PcO.OOl). Additionally, there was a significant interaction between these two factors (P<0.05). In a separate experiment, more detailed behavioural observations of the females were made of ovipositing females. The results once again showed that the prior experience treatment was not a significant explanatory variable (P>0.05) as was the host plant varieties used (P>0.05). The interaction between these two factors was statistically significant (PcO.OOl) for all of the behaviours considered. However, when the analysis of the data was repeated with the number of landings used as a covariate in the analysis, the interaction between prior experience and host plant variety was found to be non-significant (P>0.05) for all post-alighting behaviours. Therefore, it would appear that the main effect of prior experience on P. rapae is on the choice of landing site and other ovipositional behaviours are not affected.Finally, an artificial life model of the pre-oviposition behaviour of P. rapae is proposed