If you are interested in research opportunities with the Furlong Lab or Zalucki Lab on insect-plant interactions, please send me an email (firstname.lastname@example.org).
Gurion CK Ang, Myron P Zalucki & Michael J Furlong (2016) Temporal changes in olfactory and oviposition responses of the diamondback moth to herbivore-induced host plants. Entomologia Experimentalis et Applicata, 160: 28-39.
Aleni Uelese, Peter M Ridland, Richard Stouthamer, Yurong He, Gurion Ang, Myron P Zalucki & Michael J Furlong (2014) Trichogramma chilonis Ishii: a potential biological control agent of Crocidolomia pavonana in Samoa. Biological Control, 73: 31-38.
Gurion CK Ang, Rehan Silva, Sean L Maxwell, Myron P Zalucki & Michael J Furlong (2014) Contrary effects of leaf identity and position on oviposition and larval feeding in the diamondback moth. Entomologia Experimentalis et Applicata, 151: 86-96.
Gurion CK Ang, Myron P Zalucki & Michael J Furlong (2012) Menage a trois: the problem with three-way interactions involving predatory wasps. Macquarie Matrix, 2: 1-13.
Gurion CK Ang & Michael J Furlong (2012) Do predatory wasps find their prey in a three-way conversation? University of Queensland Science Undergraduate Research Journal, 1: 17-19.
The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), is the most destructive member of a complex of insect pests that attacks brassicaceous crop plants. It has been estimated to cost $4 to 5 billion worldwide annually. Adult females select suitable host plants for oviposition (= egg-laying), and larvae feed voraciously on plant foliage. Much research has focussed on inter-plant oviposition and larval-feeding responses to measure preference for and performance on different host plants. Less attention has been given to the intra-plant oviposition and larval feeding patterns, yet we know that these patterns are highly dependent upon host plant species and plant condition.
A literature survey of the oviposition patterns of P. xylostella showed that they are considered to be highly variable. However, there was much variation in bioassay methodology, and the different methods employed might influence interpretation of P. xylostella behaviour. The effect of ovipositing female density on intra-plant oviposition patterns on different host plants was tested. At higher moth densities, intra-plant oviposition patterns were different to those at low densities. This suggests that the oviposition responses of single moths or small groups of moths better reflect the field situation, where moths are unlikely to occur at such high densities under typical circumstances. Thus, it is essential that interpretation of oviposition behaviour in this species be considered in the context of how experiments were conducted.
When exposed to common cabbage, Brassica oleracea, P. xylostella laid significantly greater numbers of eggs in the basal region (lower leaves and stem) of the plant, while moths laid greater numbers of eggs on the upper leaves of larval-damaged plants, close to sites of herbivory. However, when exposed to intact Chinese cabbage, Brassica rapa, plants, P. xylostella laid significantly greater numbers of eggs on the upper leaves. In larval-damaged Chinese cabbage plants, eggs were clustered on leaves furthest away from the damaged leaf. Regardless of where eggs were laid, neonate larvae always fed on the youngest leaves of both plant species. The remainder of the experimental chapters of the thesis focus on various aspects of this contrasting preference in intra-plant oviposition patterns.
Jasmonic acid (JA) and salicylic acid (SA) have been implicated in induced plant defences to chewing and phloem-sucking herbivores respectively. Physiological crosstalk occurs between the JA and SA pathways, but their influence on intra-plant oviposition and larval-feeding patterns has yet to be studied. Host plants were manipulated with various combinations of exogenous applications of these plant elicitors to whole plants or specific leaves, and the oviposition and larval-feeding patterns that resulted from these treatments were compared with oviposition patterns in intact, and insect-damaged plants. JA and SA simulated conspecific herbivory and aphid infestations respectively. Specifically, JA could be used to manipulate oviposition patterns such that on larvae-damaged plants, where egg deposition was expected on the upper leaves, the application of JA on a lower leaf resulted in oviposition on the JA-treated leaf rather than the larval-damaged leaf. However, preference for specific sites within a plant was highly dependent on how recently a leaf was treated by either JA or exposed to larval feeding, regardless of which occurred first. In contrast, SA did not affect intra-plant oviposition patterns but significantly reduced the total numbers of eggs laid on SA-treated plants when compared with untreated controls.
Quantification of oviposition behaviours was also conducted to further explain oviposition patterns on common cabbage. On intact plants, moths always alighted on or near to the basal region of plants and laid eggs near by. While on larval-damaged plants moths alighted either on the upper leaves near where damage occurred and laid eggs near by, or travelled to these sites for oviposition after alighting on the basal region of plants. These post-alighting behaviours suggest that intra-plant host discrimination occurs in a plant condition specific manner.
Finally, headspace analyses were conducted on intact and induced plants to identify the volatile blends that may be important in mediating these oviposition patterns. In common cabbage, the herbivore induced plant volatiles (HIPVs) identified from these analyses (α-myrcene, d-limonene, and dimethyl disulphide) were used in olfactometer studies to show that attraction to these volatiles was greatly enhanced when they were presented together rather than singly. In contrast, it was shown that only green leaf volatiles (GLVs) and not HIPVs were up-regulated in induced Chinese cabbage. An important GLV, (Z) 3-hexen-1-ol, had a repellent effect on ovipositing females. These differences in plant chemistry also reflect differences in the way plants respond to herbivory, and ultimately influence P. xylostella in a host-specific manner.
Both behavioural and chemical ecology approaches were employed to better understand P. xylostella oviposition and larval-feeding behaviour, and in doing so our understanding of this species’ interaction with two of its host plants has been enhanced. The findings are discussed in the context of their significance to animal behaviour, and the implications of the work for integrated pest management of the pest.
Title: Species-specific responses of insect herbivores and their parasitoids to temporal changes in host plant volatile profiles
Plant volatiles are used as olfactory cues in host-plant recognition, selection and localization by herbivores, and for the detection of potential host herbivores by parasitoids. These volatile blends change over time, but temporal effects of these changes on herbivore and parasitoid behaviour have not been studied. In olfactometer tests, the herbivore Plutella xylostella preferred herbivore-damaged plants to intact plants. This preference declined over time, and correlated with temporal decreases in oviposition on induced plants.In contrast, another herbivore Pieris rapae did not discriminate between induced or intact plants for oviposition, suggesting that temporal changes in plant cues influence herbivore behaviour in species-specific ways. Naïve female parasitoids of these herbivores (Diadegma semiclausum and Cotesia glomerata respectively) did not discriminate between host-induced and non-host induced plants. Experienced female parasitoids not only discriminated between host-induced and non-host-induced plants, but also detected host herbivore specific induced changes in plant volatiles profiles that could be discriminated from within mixed infestations of host and non-host herbivores. Parasitism cage experiments also showed that experienced parasitoids had improved foraging efficiency relative to naïve individuals, emphasizing the importance of host experience for pre-alighting host detection and post-alighting foraging. Additionally, attraction of experienced C. glomerata to host-induced plants diminished more rapidly than attraction of experienced D. semiclausum. This suggests that it may be beneficial for specialist parasitoids like D. semiclausum to retain memory of host-specific cues to maximize foraging efficiency while generalist parasitoids like C. glomerata retain plasticity in learning cues to remain receptive to a broad range of host herbivores.