Foraging behavior of Dolichogenidea tasmanica & patterns of parasitism in light brown apple moth.

Abstract

Dolichogenidea tasmanica (Cameron) (Hymenoptera: Braconidae) is a solitary endoparasitoid that is native to Australia. I examined its response to a key pest, light brown apple moth (LBAM), Epiphyas postvittana (Lepidoptera: Tortricidae). LBAM is a native species in south-eastern Australia. D. tasmanica is known to parasitise larvae of several tortricid moths. The use of insecticides after flowering has been restricted in Australian vineyards to minimize the likelihood of pesticide residues in wine. Therefore biological control is crucial to the effective management of LBAM populations on grapes. With the long term aim of enhancing biological control in vineyards, factors that influence behaviour and population dynamics of the pest and their natural enemies must be taken into account. So in this thesis, I focused on the foraging behaviour and functional response of D. tasmanica to elucidate aspects of the biological control potential of this parasitic wasp. An understanding of the host stage preference of D. tasmanica is crucial to elucidate its role in biological control. Therefore, the first objective of my study was to determine the larval stages of LBAM that are parasitised by D. tasmanica. This study was conducted in four identical wind tunnels, using choice and no-choice tests. Here I showed that D. tasmanica parasitises the 3rd instar of LBAM, however, it was previously reported as a parasitoid of only the 1st and 2nd instars. So, D. tasmanica is capable of parasitising early larval instars, which is important for minimising pest populationsthrough biocontrol. The searching behaviour of female D. tasmanica responding to plants infested with susceptible larval stages of LBAM was studied next. Behavior was continuously recorded with event-recorder software. The elapsed time before and after taking flight from the release point until landing on an infested leaf, and the mean duration, frequency and proportion of time devoted to each type of behaviour on the leaf were analysed for each instar. These observations gave insight into how D. tasmanica interacts with hosts. I found that female D. tasmanica effectively responds to cues associated with all susceptible larval stages of LBAM to locate hosts. These experimentsshowedthat first instarLBAM is more susceptible to parasitismby D. tasmanica. Superparasitism is an important factor as it affects the stability of host-parasitoid interactions and the shape of the functional response curve. To assess the rate of superparasitism avoidance by D. tasmanica, female wasps were given choices between (i) unparasitised hosts versus freshly parasitised hosts, (ii) unparasitised hosts versus hosts at 24 h post-parasitisation, and (iii) freshly self-parasitised hosts versus hosts freshly parasitised by a conspecific female. So I investigated the frequency of superparasitism in order to evaluate whether D. tasmanica deposits its eggs in a random or non-random fashion. Experiments demonstrated that host discrimination frequently occurs in D. tasmanica. However, it appears that females are not able to discriminate the host parasitisation status prior to contacting a host. So D. tasmanica contacts hosts randomly but host acceptance is not random. The functional response of a parasitoid influences its capacity to control pests. I conducted a study to determine the type of functional response of D. tasmanica to varying densities of larval LBAM. The results showed that D. tasmanica displays a Type III functional response to varying low densities of LBAM. This suggests that it should operate in a density-dependent manner in contributing to population regulationof LBAM. Subsequently experiments were conducted to determine how recent experience affects the functional response of D. tasmanica. Results showed that D. tasmanica responds to itsexperience inahabitat, which influences the searching behaviour in the process of host location Parasitoids do not always forage alone. Individuals of a given species have similar needs for survival, growth, and reproduction, and thus will often compete for similar resources (e.g., hosts, food, nests). This may lead to a flexible patch exploitation strategy compared to the situation of a solitary forager. The foraging behaviour of single and multiple female D. tasmanica in the presence of patchily-distributed hosts was observed and analysed. Results showed that females D. tasmanica assessed patch quality instantaneously while foraging. A searching female might deposit a marking pheromone on a visited patch, which inhibits further searching and contributes to mutual interference among competitors. In this study key aspects of the individual and population behaviour of D. tasmanica were investigated. It seems that D. tasmanica can play a valuable role in the biocontrol of LBAM. The outcomes of my study should also provide insights into parasitism of other leafrollers that are susceptible to D. tasmanica. Finally the results of this research provide a foundation for understanding the biological control potential of D. tasmanica against LBAM in vineyards. Further research is needed to investigate how factors such as host plant preference, alternative host species, the availability of floral resources and interspecific competition influence patterns of parasitism by this species.