Daniel Coderre

INTRAGUILD PREDATION AMONG APHID PREDATORS: CHARACTERIZATION AND INFLUENCE OF EXTRAGUILD PREY DENSITY

Intraguild predation (IGP), a common interaction in invertebrates and vertebrates, affects the abundance and distribution of many species. Several parameters influence the magnitude and direction of IGP: feeding specificity, size, mobility, and aggressiveness of the protagonists, as well as extraguild prey density. Under laboratory conditions, we studied IGP among three species of aphid predators, Aphidoletes aphidimyza (Diptera: Cecidomyiidae), Chrysoperla rufilabris (Neuroptera: Chrysopidae), and Coleomegilla maculata lengi (Coleoptera: Coccinellidae), which commonly attack the potato aphid (extraguild prey) Macrosiphum euphorbiae (Homoptera: Aphididae). We characterized the levels and symmetry of IGP among the various stages of the predators in the absence of extraguild prey. The aphid specialist A. aphidimyza was more vulnerable to IGP than C. rufilabris and C. maculata, two generalist predators. The C. maculata/C. rufilabris interaction was symmetric (mutual IGP), whereas the C. maculata/A. aphidimyza and C. rufilabris/A. aphidimyza interactions were asymmetric, in favor of the coccinellid and the lacewing, respectively. Sessile and low mobility stages of all species were extremely vulnerable to IGP. Generally, the larger sized individual won confrontations. For similar sizes, lacewing larvae were superior to coccinellid larvae. We also tested whether IGP decreases when extraguild prey are introduced into the system. Data from five predator combinations revealed three types of responses: (1) an exponential decrease in IGP (lacewing instar I vs. coccinellid instar I); (2) a constant IGP (lacewing instar III vs. coccinellid instar I); (3) a constant IGP at low densities decreasing at high densities (lacewing instar III vs. gall midge old larva). Four theoretical scenarios are derived from these responses. Each is discussed according to the ecological attributes of the protagonists. This study shows that IGP is influenced by factors inherent to the predators and external factors such as extraguild prey density. The results are discussed further in the context of aphid biological control.

Voracity and feeding preferences of two aphidophagous coccinellids on Aphis citricola and Tetranychus urticae

Voracity and feeding preferences of adult Coccinella septempunctata L. and Harmonia axyridis Pallas (Coleoptera: Coccinellidae, tribe Coccinellini) were evaluated in the laboratory on a common prey, the spirea aphid, Aphis citricola van der Goot (Homoptera: Aphididae), and on the twospotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), a prey previously unrecorded for these two predators. The experiments were carried out in the laboratory on apple saplings (Malus domestica Borkhausen). Adult males and females of H. axyridis consumed significantly more mites than adults of C. septempunctata. For H. axyridis, males consumed 41.3 spider mites in 24 h and females 48.4, whereas for C. septempunctata males consumed 14.1 prey and females 15.2. The consumption of spirea aphids by the males was similar for the two species. Consumption by the females was significantly greater for H. axyridis (46.5) than for C. septempunctata (22.2). The two coccinellids showed a significant preference for A. citricola in the presence of T. urticae. This preference was more pronounced for C. septempunctata. The total number of prey consumed and the percentage of exploited biomass decreased significantly for C. septempunctata and stayed relatively constant for H. axyridis as the number of mites increased in the prey ratio. Our results suggest that T. urticae is only an alternative prey for both predators, and that H. axyridis should be more efficient than C. septempunctata in a prey assemblage with aphids and mites.

Heavy metal-specific inhibition of phagocytosis and different in vitro sensitivity of heterogeneous coelomocytes from Lumbricus terrestris (Oligochaeta)

Cell viability and phagocytic activity of coelomocytes from the gastrointestinal tract of Lumbricus terrestris were examined by flow cytometry after in vitro exposure to heavy metals. Control coelomocytes were incubated for 18 h at 15 degrees C, 5% CO2, in Ca(++)-containing LBSS medium with 10(-4)-10(-9) M mercury chloride, methylmercury, cadmium chloride, zinc chloride, lead chloride or lead acetate. Heterogeneity of coelomocyte population was demonstrated by forward scatter (FSC) analysis and cytometric profile showing two different populations of type I/small (60%) and type-II/large (40%) cells. Exposure to either form of Hg, Cd and Zn was relatively highly toxic and affected both cell viability and phagocytosis, whereas Pb was relatively well tolerated by the coelomocytes. A fraction of cells within large coelomocyte population was exceptionally sensitive to the Hg-induced cytotoxicity, which did not affect, however, the relative phagocytic activity of the remaining cells. Overall, at least three different patterns of metal-specific toxicity, affecting both viability and phagocytic functions of earthworm coelomocytes, were confirmed in our in vitro studies. Further characterisation of both the target cells from heterogeneous coelomocyte population and the specific interaction of target cell-xenobiotic can possibly reduce biomonitoring problems in earthworm toxicology and immunotoxicology.

Differential prey utilization by the generalist predator Coleomegilla maculata lengi according to prey size and species

Prey utilization by the generalist predator Coleomegilla maculata lengi Timb. (Coleoptera: Coccinellidae) of three sympatric lepidopterous species was quantified in relation with prey size (age) and prey species. Based on optimal foraging theory, we argued that costs associated with the utilization of small and large prey are higher than those of intermediate prey size. As a result, we expected a higher prey consumption rate on intermediate prey size leading to a convex prey consumption curve. Laboratory experiments showed that, within a given prey instar, Coleomegilla maculata lengi preyed more on Plutella xylostella (L.) compared to Artogeia rapae (L.) and Trichoplusia ni (Hübner). Generally, prey consumption rate by Coleomegilla maculata lengi on the three prey species decreased with increasing immature prey size (age). The predation efficacy of Coleomegilla maculata lengi adults and fourth instar larvae was higher compared to younger coccinellids (L2). Although, Coleomegilla maculata lengi showed a higher level of predation on smaller immature prey, we demonstrated that it is not the optimal size range for this predator. As predicted, prey weight consumption rate by Coleomegilla maculata lengi was higher at intermediate prey size leading to a convex prey utilization curve. The beneficial impact of Coleomegilla maculata lengi predation on the host plant was also estimated by using a Protection Index that considers the differential predation caused by the coccinellids and the relative importance of each pest species in terms of plant injury. Coleomegilla maculata lengi has a more significant beneficial impact when it preys on T. ni immatures.

Can Developmental and Behavioral Characteristics of the Multicolored Asian Lady Beetle Harmonia Axyridis Explain its Invasive Success

Major impacts of biological invasions are widely recognized and underscore the need to understand the relation between life-history traits of invasive species and the invasion process. Growth of juveniles and adult survival of invasive species are key factors in invasion process. Life-history traits that increase juvenile fitness including increased rates of development and behavioral characteristics that facilitate competitive success such as increased predator efficiency and foraging ability may explain invasiveness of a species. Invasion of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) in North America provides an opportunity to investigate life-history traits of juveniles of an invasive species. Here, we evaluate both developmental and behavioral traits that may explain the success of H. axyridis by comparing it to an ecologically similar indigenous species Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Three points may contribute to the invasiveness of H. axyridis. First, development of H. axyridis was faster during the 2nd larval instar than C. maculata, a characteristic that may reduce vulnerability at young instars. Second, H. axyridis reached the 4th instar more rapidly than C. maculata. The 4th instar of H. axyridis was also characterized by higher predation efficiency with increased voracity, lethal contact and search efficiency of pea aphids Acyrthosiphon pisum. Finally, surprisingly, a 5th larval instar occured in 33% of the individuals of H. axyridis and was characterized by the same developmental time, but with increased voracity and weight gain compared to 4th larval instars, suggesting an increased fitness of these individuals. These developmental characteristics coupled with increased predation efficiency and behavioral characteristics enhanced the juvenile growth and predatory abilities of this species and may contribute to the invasive ability of H. axyridis.

Effect of Temperature and Intraspecific Allometry on Predation by Two Phenotypes of Harmonia axyridis Pallas (Coleoptera: Coccinellidae)

Abstract Harmonia axyridis Pallas is a highly polymorphic coccinellid with a wide geographic distribution. Genetic polymorphism seems to be the strategy adopted for facing different habitats at different times. Many modifications, such as body shape, body size, and elytral patterns, may be adaptive through imparting increased tolerance to adverse conditions. Previous studies evaluating differences in the light-colored aulica and dark colored nigra phenotypes found differences in biological performances at 20°C. However, whether the predatory activity of the different phenotypes changes under different temperatures remains unknown. Relative consumption rate and predation activity of fourth instars and adults of aulica and nigra phenotypes were compared at 10, 15, 20, 25, and 30°C. Our results showed that temperature is a limiting factor to larval and adult relative consumption rate. The thermal optimum of nigra adults was 3.7°C lower than that of aulica. Both larvae and adults of nigra were more stenothermic than aulica. Close to the upper limit of tolerance (30°C), predation activity of nigra adults was more affected than aulica. In larvae body size and shape could explain the differences observed, because aulica is significantly bigger than nigra and thus aulica presumably can better control heat exchange.

Changes in soil macroarthropod communities in relation to forest maturation through three successional stages in the Canadian boreal forest

Abstract The edaphic macroarthropod communities of three sites representative of the forest succession in the Lake Duparquet region (situated in the southern part of the boreal forest, Abitibi, Quebec, Canada) were studied. A 47-year-old deciduous forest, a 144-year-old mixed forest, and a 231-year-old coniferous forest form a successional forest gradient with a vegetation composition that is a function of the time elapsed since the last forest fire. Along with forest succession, there is a reduction in macroarthropod community biodiversity. There is a negative gradient for mean total abundance (237–41 individuals), total richness (63–23 species), density (1792–661 individuals/m2), diversity (H′ = 1.478–1.007) and equitability (J = 0.821–0.739). These community changes affect saprophagous organisms more than predators. Certain species or taxa show preferences for a particular forest type, such as larval Diptera for the deciduous forest. A comparison of these results with the literature suggests an inverse preference as to habitat choice between microarthropods (Acarina and Collembola) and macroarthropods. From a conservation point of view, macroarthropod biodiversity will be favored by the protection of all forest types since each environment possesses a particular community structure and species.

Egg cannibalism by Coleomegilla maculata lengi neonates: preference even in the presence of essential prey

Abstract 1. Egg cannibalism among coccinellids has been reported widely, however reasons why this type of behaviour is observed so frequently have been neglected. This experiment was undertaken to clarify whether cannibalistic behaviour is advantageous to Coleomegilla maculata lengi Thimberlake neonates and to understand the reasons for high levels of egg cannibalism.

Influence of prey quality on the fitness of two phenotypes of Harmonia axyridis adults

The performance of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) adults of the aulica and nigra phenotypes fed on Aphis fabae Scopoli and Myzus persicae (Sulzer) was compared by measuring their voracity, daily biomass consumption, daily weight gain, efficiency of food utilisation, and reproductive capacity. Our results demonstrated differences in the suitability of A. fabae and M. persicae for the two phenotypes of the predator. This suggests that either differences occur in the nutritive requirements of the predators, or in the nutritive value of the two prey species. Both A. fabae and M. persicae supported the growth and oviposition of the aulica and nigra phenotypes. Although nigra females consumed fewer M. persicae, they achieved the same daily weight gain as aulica females. The predator phenotypes consumed the same amount of A. fabae, but the daily weight gain of aulica females was higher than that of nigra. The two predator phenotypes had the same feeding efficiency when consuming M. persicae or A. fabae. The reproductive capacity of nigra females was higher, when this phenotype consumed A. fabae rather than M. persicae.

Evaluation of earthworm exposure to contaminated soil by cytometric assay of coelomocytes phagocytosis in Lumbricus terrestris (Oligochaeta)

Abstract We measured non-specific immunity of the earthworm species Lumbricus terrestris by flow cytometric evaluation of coelomocytes phagocytosis activity. In vivo and in vitro phagocytosis of fluorescent microspheres by coelomocytes were quantitated 18 h following intra coelomically injections of microspheres or in vitro incubation of phagocytes with the microspheres. Then, cytometric evaluation of cell-associated fluorescence was performed using a FACScan (Becton Dickinson). Earthworms were washed, placed in extrusion medium containing 5% ethanol. Following the contractions, the coelomocytes were collected. The cells were washed and resuspended in appropriate medium. The flow cytometric acquisitions were performed immediately for in vivo phagocytosis or after 2, 18, 24 and 48 h during in vitro kinetics. Preliminary results showed significant in vivo and in vitro phagocytic activity of microspheres by coelomocytes. Application of flow cytometry for validation of cellular and functional variables in earthworms appears to be a promising approach. Thus, our data showed that cytometric determination of phagocytic activity of coelomocytes with synthetic microspheres can be applied for validation of non-specific immune response in the earthworm species, Lumbricus terrestris .