THE OVIPOSITION BEHAVIOUR OF THE BLACK VINE WEEVIL Otiorhynchus sulcatus (FABR)

Abstract

Within the constraints of the experiments conducted vine weevil were found to exhibit a strategy of volume of indiscriminate oviposition rather than a strategy of definitives it eselection characteristic of a true oviposition behaviour. A series of experiments was conducted to determine oviposition and host plant interactions under conditions of choice and absence of choice of host plant. It was found that oviposition was greatest for Yew, followed by polyanthus, fushcia, strawberry and (despite the name) was found to be least on vine plants. Variation was attributed to a combination mainly of ground cover and partially quality of host. Oviposition was found to be much lower under conditions of absence of choice. Variation was attributed to the observation that not all vine weevil oviposit all the time and that feeding and oviposition upon a plant are independent. A further experiment conducted using strawberry plants with variable leaf N reinforced the interpretation that feeding and oviposition are independent functions. Under conditions of choice of host plant it was found that feeding occurred upon plants that were not capable of generating ova. Passive transponders attached to individual vine weevil adults were Utilised in order to relate oviposition and feeding to specific actions of individual vine weevil. If was found that a greaterv olume of leaf matter was consumed from leaves of high N that was not associated with an increase in plant visitation. It was also found that the presence of surface refuge increases the volume of oviposition and feeding- possibly as a function of increasing the number of vine weevil that remain in association with the host plant. Direct measurement of leaf area consumed reinforced the observation that feeding and oviposition are not correlated. Transponder signals that indicate that more than one weevil is present at 4 an oviposition site suggests that vine weevil do not have the need to be alone when ovipositing. The distribution of oviposition is highly influenced by locomotion. Traditional arena based studies suggested the high level of incidence of directional bias. In order to determine the angle of rotation and the path length an item of apparatus was designed a nd created. The AVOID apparatus enabled the measurement of path and angle without the detrimental effect of an arena wall. The avoid apparatus was used to determine the variables related to locomotion for a comparison of pre-oviposition weevil locomotion with post oviposition locomotion, the effect of nutritional state upon locomotion and the effect of crowding. Observations uggests that vine weevils that have oviposited have a greater tendency to remain inactive than pre-oviposition vine weevils,which may result in an increased level of dispersal of pre-oviposition vine weevils. The contribution to dispersably larval stage0 . sulcatus was determined.It was found that third instar vine weevil larvae are highly mobile. It is theorised that the artificial barrier created by a plant pot prevent dispersal and,thus, exacerbate the larval status as a pest. An attempt was made to develop a molecular biology technique to differentiate the ova produced by multiple vine weevils at an oviposition site. It was determined that sufficient DNA could be extracted from a single ovum to enable several PCR reactions. A theoretical model of the inheritance of mtDNA molecules was created to test the feasibility of mtDNA mutation as a differentiation method.