[Show abstract][Hide abstract] ABSTRACT: While carnivores are known to be attracted to herbivore-induced plant volatiles, little is known about how such volatiles may affect the behaviour of omnivorous predators that may use both plants and herbivores as food. Here, we examine how systemically produced plant volatiles, in response to local herbivore damage, differentially attract a key omnivorous predator, (Heteroptera: Anthocoridae), to single clones of three species of : , and . The profiles of the plant volatiles produced were found to vary among clones and between herbivore-damaged and intact plants. was attracted to the volatiles released from undamaged plants of all three species, but most strongly to a native clone. Plants damaged by the herbivorous leaf beetle (Coleoptera: Chrysomelidae) were generally more attractive than undamaged plants, with responding to systemic changes in the damaged plants where the experimental design specifically excluded volatiles released from the actual site of damage. When comparing damaged plants, the clone was more attractive to than the clone-a somewhat surprising result since this clone is considered relatively resistant to , and hence offers a limited amount of prey. Our experiments highlight that both constitutive and induced plant volatiles play a role in omnivore attraction, and this emphasizes the importance of considering odours of released volatiles when cropping and breeding for increased resistance to herbivores.
[Show abstract][Hide abstract] ABSTRACT: The family of cecidomyiid midges (Diptera: Cecidomyiidae) exhibits diversified patterns of life history, behavior, host range, population dynamics and other ecological traits. Those that feed on plants include many important agricultural pests; most cultivated plants are attacked by at least one midge species. Several features of the reproductive biology of cecidomyiid midges point to an important role for chemical communication, with this topic last reviewed comprehensively 12 years ago. Here, we review progress on identification of sex pheromones, chemicals involved in location of host plants, the neurophysiology of reception of volatile chemicals, and application of semiochemicals to management of pest species of cecidomyiid midges that has occurred during the last decade. We hope this review will stimulate and sustain further research in these fields.
No preview · Article · Jan 2012 · Journal of Chemical Ecology
[Show abstract][Hide abstract] ABSTRACT: This study describes the morphology and function of the antennal sensilla in two gall midge species, Contarinia nasturtii and Mayetiola destructor, where multi-component sex pheromones have been identified. Both species possess sensilla trichodea, s. coeloconica, s. chaetica and s. circumfila. Sensilla circumfila, which consist of several sensilla that bifurcate and fuse into one structure, are unique for the gall midges. In C. nasturtii s. circumfila are sexually dimorphic. In males, they form elongated loops suspended on cuticular spines, whereas in females they run like worm-like structures directly on the antennal surface. Single sensillum recordings demonstrated that olfactory sensory neurons housed in male s. circumfila in C. nasturtii responded to the female sex pheromone. In M. destructor, s. circumfila were attached to the antennal surface in both sexes, and displayed no response to sex pheromone components. A sexual dimorphism was also found in the number of s. trichodea per antennal segment in both C. nasturtii (male 1 vs. female 7) and M. destructor (male 13 vs. female 10). OSNs located in male M. destructor s. trichodea responded to the sex pheromone. This is the first gall midge single sensillum study, and the first demonstration of the functional significance of s. circumfila.
[Show abstract][Hide abstract] ABSTRACT: The swede midge, Contarinia nasturtii Kieffer, is a serious pest in crucifers. Its pheromone is a blend of (2S,9S)-diacetoxyundecane, (2S,10S)-diacetoxyundecane and (2S)-acetoxyundecane. The pheromone is used in monitoring traps, and this study examines possible ways to optimise the traps.
Two dispenser types were compared: polyethylene dispensers and cotton dispensers. Polyethylene dispensers attracted male C. nasturtii for more than 6 weeks, whereas cotton dispensers were attractive for only 2 weeks. All three pheromone components were important for attraction of male midges in the field. The importance of the stereoisomeric compositions of the pheromone compounds was also tested-both in the wind tunnel and in the field. In the case of 2,9-diacetoxyundecane and 2-acetoxyundecane, the non-natural stereoisomers did not inhibit male C. nasturtii attraction, whereas one or both of the stereoisomers of 2,10-diacetoxyundecane did.
Pheromone traps with the synthetic pheromone in a 1:2:0.02 ratio emitted from PE dispensers were highly effective and long lasting. As the mixture of stereoisomers of 2,10-diacetoxyundecane strongly inhibited attraction of male C. nasturtii while those of 2,9-diacetoxyundecane and 2-acetoxyundecane did not have any inhibitory effect, it is possible to produce traps that are effective and long lasting but cheaper to produce and maintain.
No preview · Article · Aug 2009 · Pest Management Science
[Show abstract][Hide abstract] ABSTRACT: Charles Darwin is the father of evolution as we know it today. In his book “The origin of species” he states that new species originate from ancestral species that change over time, and that the mechanism of the change is natural selection. How the variation natural selection need is generated and passed from generation to generation was solved by Gregor Mendel and Thomas Hunt Morgans (and his group). Based on experiments with pea plants, Mendel formed laws about segregation and assortment of traits and Morgans group demonstrated that Mendels hypothetical factors are specific points on the chromosome.
Evolution mostly deals with how populations become adapted to their environment, but not how this adaption leads to speciation. For speciation to occur, barriers for the gene flow between populations have to evolve. There are two general modes of speciation defined by how the gene flow between populations is interrupted. In allopatric speciation a physically barrier isolates a population, whereas sympatric speciation occur within a single geographical area and reproductive isolation arises between individuals that always have the opportunity to interbreed.
Insects are good models when the mechanisms underling evolution and speciation are studied, there are more than one million species and their diversity and distribution is amazing. Olfaction is the primary sense by which the environment is interpreted by insects, and olfactory cues can be important for separation of population evolving in sympatry. That was demonstrated by Löfstedt and co-workers who studied nine species of sympatric ermine moth Yponomeuta. All species had a mixture of (E)-11 and (Z)-11 tetradecenyl acetate as primary pheromone compounds, however, the females produced the compounds in a specific ratios that never overlapped if the species were not isolated by other barriers.
Pheromones are well studied compared to the plant-produced odors. However, insects can detect relevant plant odors with the same selectivity and sensitivity as they detect pheromones. The number of volatiles emitted from fruit and plants is much higher than the number of components in the female pheromone, yet, Stensmyr et al. (2003) demonstrated that Drosophila melanogaster only needs a few key components to locate and detect a food source.
The Rhagoletis pomonella sibling species complex is a model system for sympatric host race formation and speciation (e.g. Forbes et al., 2005; Linn et al., 2003; Linn et al., 2005b). The complex consists of several strains with different host preference – a preference based on olfactory cues. Host choice is of evolutionary significance for Rhagoletis as they mate on or near the fruit of their respective host plant. Adult flies tend to mate on or near the same species of host fruit as the one they infested as larvae. Thus, differences in host preferences can translate into mate choice and can act as pre-mating barriers to gene flow.
As for other insects, gall midge behavior has been shown to be guided by olfactory cues; they use pheromones when locating a suitable mate and plant volatiles for host plant recognition. Thus, host plant volatiles might be important when gall midges shift between hosts and subsequently in the formation of new gall midge species. In my thesis I will study possible evolutionary mechanisms behind the great diversity of the gall midges. The two main questions I will address in my thesis are: do gall midges associated with the same host plant use the same or a similar set of odors to identify it? And, conversely, do closely related species that have different host plant requirements respond to odors common for the different plants?