Stratégies de ponte et d'alimentation larvaire chez la pyrale de la canneberge, Acrobasis vaccinii (Lepidoptera: Pyralidae)

Authors: Marchand, David
Advisor: McNeil, Jeremy Nichol
Abstract: In insect species whose larvae need several hosts to complete their development, larval survival is usually dependent on both the choice of oviposition sites by females and the food searching behaviour of larvae. In this thesis, I studied oviposition behaviour and larval foraging behaviour and their possible impacts on larval fitness in the cranberry fruitworm, Acrobasis vaccinii (Lepidoptera: Pyralidae), a species in which each larva must feed on several fruits of the cranberry, Vaccinium oxycoccos (Ericacae), to complete its development. Firstly, I demonstrated that females, under laboratory conditions, exhibit a significant preference for the largest fruit available when choosing oviposition sites; larvae leaving these maternally selected large fruits were significantly larger than those larvae leaving smaller fruits. In the field, however, this preference based on fruit size was not observed. This lack of preference in nature may be due, in part, to the fact that the oviposition period of A. vaccinii is relatively early during the summer when cranberry fruits are still small and when there is little variation in the size of fruits available. I also found a heterogeneous distribution of hosts in patches of varying fruit densities, and a large variability in fruit production between the two years of my study. The fact that, in any given year, hosts may be rare may be a reason why females accept relatively low-quality hosts (i.e., relatively small fruits). Thus, this study demonstrates a behavioural plasticity in A. vaccinii, females selecting largest fruits only when environmental conditions are good (such as in our laboratory conditions). A second study on larval feeding behaviour demonstrated that green cranberry fruit become red following attacks by A. vaccinii larvae. This host modification (fruit colour) may be a cue used by conspecific larvae to avoid already infested fruits, thus reducing the risk of intraspecific competition. I also showed that A. vaccinii larvae are able to take into account two other factors - fruit size and distance between hosts - in their choice of fruit. Larvae of A. vaccinii show behavioural plasticity when choosing fruit in that they accord a different degree of importance to each factor (fruit size, fruit colour and distance between fruit) depending on the context. This plasticity allows the larvae to maximise foraging efficiency while minimising intraspecific competition and predation risk.
Document Type: Thèse de doctorat
Issue Date: 2003
Open Access Date: 11 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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