Jacques Brodeur

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. n nWe 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.

Relationship Between Temperature and Developmental Rate of Stethorus punctillum (Coleoptera: Coccinellidae) and Its Prey Tetranychus mcdanieli (Acarina: Tetranychidae)

Abstract Temperature affects insect and mite development, allowing species-specific traits including optimal temperature and low and high temperature thresholds to be observed. Development rate models and biological parameters estimated from them can help determining if synchrony exists between pests and natural enemies. We studied development of the coccinellid Stethorus punctillum Weise and the spider mite Tetranychus mcdanieli McGregor at 12 constant temperatures ranging 10–38°C (±0.5°C), and modeled their development rates as a function of temperature. This predator-prey complex is typical of red raspberry, Rubus idaeus L., in Quebec, which is characterized by a short season. Eleven published models were compared for accuracy in predicting development rate of all stages of both species, and estimating their temperature thresholds and optima. The spider mite developed to the adult stage in the 14–36°C range, compared with 14–34°C for the coccinellid. Males and females did not differ, and the development rates steadily increased from 14 to 30°C, leveling off in the range 34–36°C for the spider mite, or 30–32°C for its predator. Most models were rejected for failure to satisfy criteria of goodness-of-fit and estimable temperature threshold parameters. The Lactin-2 model for T. mcdanieli and the Brière-1 model for S. punctillum, were superior at estimating low temperature threshold, which is critical where temperatures are frequently low in the spring, and were separately fitted to all development stages of both organisms. Based on the predictable early spring development of S. punctillum and T. mcdanieli, the results indicate potential synchrony between them.

Intraguild interactions in aphid parasitoids

We reviewed the literature on aphid parasitoids to determine the occurrence, nature and outcome of intraguild interactions. Intraguild interactions were described for larval, pupal and adult aphid parasitoids and by the type of natural enemy (fungus, predator, or parasitoid). They appear to be prevalent in most aphid parasitoid systems and, except for parasitoid‐parasitoid interactions, they are mostly asymmetric, with aphidophagous predators and pathogens killing parasitoids. The limited experimental evidence from field studies is insufficient to provide a comprehensive pattern of the consequences of intraguild interactions for aphid parasitoid populations in general and, more specifically, for the efficacy of biological control. However, because intraguild interactions are widespread in aphid‐natural enemy communities and mostly detrimental to aphid parasitoids, we conclude that intraguild interactions have a primary effect in driving fluctuations in aphid parasitoid populations. Drawing on case studies, we further argue that intraguild interactions can substantially alter the effectiveness of aphid parasitoids as biological‐control agents.

Seasonal microhabitat selection by an endoparasitoid through adaptive modification of host behavior

Differences in the distribution of parasitized and unparasitized hosts has been used to infer modification of host behavior by insect parasitoids. Data are presented showing that not only do parasitized hosts behave differently from unparasitized ones, but that the behavior of parasitized hosts varies in function of the physiological state of the parasitoid. Aphids containing nondiapausing parasitoids leave the aphid colony and mummify on the upper surface of the leaves, whereas those containing diapausing parasitoids leave the host plant and mummify in concealed sites. Modification of host behavior by diapausing parasitoids results in the selection of a suitable microhabitat that reduces the incidence of hyperparasitism and should decrease the action of adverse climatic conditions during the lengthy dormant period.

Effect of temperature on intrinsic rates of natural increase (rm) of a coccinellid and its spider mite prey

The intrinsic rate of natural increase(rm) is useful to estimate the populationgrowth potential of insects and mites, whichmay help predict the outcome of pest-naturalenemy interactions. This study was conductedto determine how 12 constant temperatureregimes between 10–38 °C (± 0.5 °C) may differentially affect therm of the McDaniel spider mite, Tetranychus mcdanieli McGregor (Acarina: Tetranychidea), a common pest of raspberry, andits coccinellid predator, Stethoruspunctillum Weise (Coleoptera: Coccinellidae). Tetranychus mcdanieli survived tomaturity in the 14–36 °C range, comparedto the 14–32 °C range for S.punctillum. Survival above 24 °Cremained high for the spider mite, butdecreased markedly for the coccinellid. Tetranychus mcdanielis range forreproduction was similar to its survival range,but S. punctillum failed to reproduce at14 °C and reproduced only poorlyat 16 °C. Offspring production peakedat 24 °C for both T. mcdanieli(average 152 eggs per female), and S.punctillum (280 eggs per female). At alltemperatures suitable for reproduction, femalelongevity of the coccinellid was greater thanthe spider mite, which was characterized byearlier/faster reproduction than thecoccinellid. As temperature increased, therm followed a typical asymmetricaldome-shape pattern, with maximum values of0.196 d−1 and 0.385 d−1at 30 °C and 34 °C, for S.punctillum and T. mcdanieli,respectively. For each species, therm-temperature relation was successfullymodelled using a curvilinear regressionequation previously shown to predictdevelopment rate. In both species, thedevelopment rate response to temperature has amajor influence on the temperature-rmrelationship. In the 16–32 °C rangesuitable for population growth of both species,the rm of T. mcdanieliwas 1.9 (30 °C) to 8 (16 °C) times greaterthan S. punctillum. These growthpotential ratios are consistently in favor ofthe prey, suggesting a limitation of thecoccinellid with respect to its capacity totrack T. mcdanieli populations. However,under short season conditions, the inferiorreproductive dynamics of S. punctillumsvs. spider mite prey should not have aprevailing influence in determining impact, andmay be compensated by high voracity incombination with a strong aggregativeresponse.

Host behaviour modification by the endoparasitoid Aphidius nigripes: a strategy to reduce hyperparasitism

Abstract. 1. One possible component of successful parasitism by insect parasitoids is the reduction of predation and hyperparasitism through the modification of host behaviour.

Intraguild predation in biological control and conservation biology

Abstract Intraguild predation has become a major research topic in biological control and conservation ecology. Theoretical studies on intraguild predation have advanced in food web ecology and point towards basal resources being an important predictor of the outcome and the stability of intraguild interactions. Here we introduce the concept of intraguild predation and highlight the complexity of ecological interactions that may arise in natural multi-predator systems due to species diversity and patterns of abundance. We discuss the application of intraguild predation in biological control programs and conservation management, and suggest that productivity gradients should be considered in future experiments.

Pathogenicity of the fungus Verticillium lecanii to aphids and powdery mildew

Aspects of the host specificity and pathogenicity of the hyphomycete, Verticillium lecanii , were investigated under laboratory conditions. DiVerences were observed in the pathogenicities of three strains of V. lecanii (DAOM 198499, DAOM 216596 and Vertalec) to the potato aphid Macrosiphum euphorbiae and Sphaerotheca fuliginea , the causal agent of cucumber powdery mildew. The estimated median lethal concentration required to achieve 50% mortality (LC ), 50 median lethal time leading to 50% mortality (LT ) and aphid net reproductive rate ( R ) 50 0 indicated that Vertalec and strain 198499 were more virulent to aphids than strain 216596. The estimated median colonization time for 50% of fungal colonies (CT ) showed that strain 50 198499 was the best antagonist of cucumber powdery mildew. Further comparison suggested that the mean pathogenicity of V. lecanii strain 198499 to cucumber powdery mildew was almost equivalent to that of Sporothrix flocculosa , a biological control agent of greenhouse fungal path...

Ultrastructural and Cytochemical Investigations of the Antagonistic Effect of Verticillium lecanii on Cucumber Powdery Mildew

ABSTRACT Chronological events of the intercellular interaction between Verticillium lecanii and cucumber powdery mildew, caused by Sphaerotheca fuliginea, were investigated at different times after inoculation by transmission electron microscopy. V. lecanii hyphae colonized host structures by tight binding, apparently mediated by a thin mucilaginous matrix. As early as 24 h after application of the antagonist, increased vacuolation and disorganization of the cytoplasm of the pathogen hyphae were easily detected. By 36 h after treatment, plasmalemma retraction and local cytoplasm aggregation were typical features of damage. Labeling chitin with the wheat germ agglutinin (WGA)/ovomucoid-gold complex showed that intracellular invasion of S. fuliginea by V. lecanii did not cause extensive host cell wall alterations, except in the area of hyphal penetration. By 48 h after inoculation, further cytoplasm disorganization was observed, as evidenced by the loss of cell turgor and contortion of the cell wall. Such deformation suggests that penetration of the antagonist results from mechanical pressure or localized enzymatic hydrolysis through the action of chitinases, as confirmed by the pattern of labeling obtained with the WGA/ovomucoid-gold complex. By 72 h after contact between the fungi, S. fuliginea cells were markedly collapsed, depleted of their protoplasm due to extensive multiplication of the antagonist, and totally encircled by the antagonist. Based on the current observations, the antagonism of S. fuliginea by V. lecanii appears to involve the following events: (i) attachment of the antagonist to the powdery mildew fungus; (ii) mechanical pressure and production of cell-wall degrading enzymes such as chitinases; (iii) penetration and active growth of the antagonist inside the pathogen hyphae; and (iv) digestion of host tissues and release of the antagonist from dead cells of S. fuliginea. The interaction between V. lecanii and S. fuliginea also affected the morphological and structural features of the haustorial bodies, as shown by increased vacuolation, distortion, and necrotization of the haustorial lobes. These observations provide the first experimental evidence that V. lecanii, primarily known as an entomopathogenic fungus, also has the potential to colonize mycelial structures of S. fuliginea. V. lecanii, therefore, may become a valuable alternative to current management of cucumber powdery mildew in greenhouses.

Inhibition of fungal growth in thermoregulating locusts, Locusta migratoria, infected by the fungus Metarhizium anisopliae var acridum

The locust, Locusta migratoria, has the capacity to develop a behavioural fever which reduces fungal infection by Metarhizium anisopliae var acridum. We investigated hemocyte and blastospore kinetics in infected insects under conditions that did or did not allow thermoregulation. Hemocyte concentrations were severely reduced in inoculated insects that did not thermoregulate but remained similar to those of controls in inoculated insects that were allowed to thermoregulate. Reductions in hemocyte counts were accompanied by an increase in the concentration of blastospores. In non-thermoregulating insects, circulating blastospores were first observed two days post-inoculation and had heavily colonized the hemolymph by day 5; in contrast, no blastospores were recovered from hemolymph of inoculated-thermoregulating insects. We used fluorescein isothiocyanate (FITC)-labelled silica beads to examine in vivo phagocytosis in thermoregulating and non-thermoregulating locusts. In the absence of fungus, a greater proportion of beads were engulfed by hemocytes in thermoregulating than in non-thermoregulating locusts early (4 and 24h) after bead injection, but the proportions were similar thereafter. In infected locusts, phagocytosis in non-thermoregulating insects was progressively impaired; such impairment, however, was not observed in challenged, thermoregulating insects. Our results suggest that thermoregulation helped keep fungal growth in check, apparently through the maintenance of hemocyte population levels and the direct inhibition of blastospore propagation by elevated temperatures.