Discrimination of parasitized aphids by a hoverfly predator: effects on larval performance, foraging, and oviposition behavior

The choice of oviposition site by female aphidophagous predators is crucial for offspring performance, especially in hoverflies whose newly hatched larvae are unable to move over large distance. Predator and parasitoid interactions within the aphidophagous guild are likely to be very important in influencing the choices made by predatory hoverfly females. In the present study, the foraging and oviposition behavior of the aphidophagous hoverfly Episyrphus balteatus DeGeer (Diptera: Syrphidae) was investigated with respect to the parasitized state of its aphid prey, Acyrthosiphon pisum Harris (Homoptera: Aphididae), that were parasitized by Aphidius ervi Haliday (Hymenoptera: Aphidiidae). We also recorded the number of eggs laid by hoverfly females when subjected to parasitized aphids. Furthermore, we studied the influence of being fed with parasitized aphids on hoverfly larval performance. Hoverfly females did not exhibit any preference for plants infested with unparasitized or aphids parasitized for 7 days. On the other hand, plants infested with mummies or exuvia were less attractive for E. balteatus. These results were correlated with (i) the number of eggs laid by E. balteatus females and (ii) larval performance. Thus, our results demonstrate that E. balteatus behavior is affected by parasitoid presence through their exploitation of aphid colonies. Indeed, hoverfly predators select their prey according to the developmental state of the parasitoid larvae

Exploring the factors involved in the absence of parasitism of Chaetosiphon fragaefolii by generalist parasitoids in strawberry

Chaetosiphon fragaefolii Cockerell (Hemiptera: Aphididae) is a worldwide strawberry pest with scarce records of parasitoids for its control. The parasitization rate of two generalist parasitoids, Aphidius colemani Viereck and Aphidius matricariae Haliday, their behavior and aphid defensive behaviors were evaluated with Aphis gossypii Glover (Hemiptera: Aphididae) as a comparative host. Defensive endosymbionts were also surveyed. C. fragaefolii was never parasitized in simple-choice tests, whereas in preference tests both parasitoids chose A. gossypii over C. fragaefolii. No contacts of A. matricariae with C. fragaefolii were observed while A. colemani made more antennal contacts and “stings” on A. gossypii than on C. fragaefolii with the latter exhibiting less defensive behaviors against the parasitoid. The bacterium Acinetobacter sp. was detected in all samples of C. fragaefolii, but with an unknown function. Further research on the possible defensive role of the glandular hairs covering the body of this aphid, the role of chemical signals and the existence of defensive internal mechanisms against parasitoids could provide plausible explanations for the absence of parasitism found.Instituto de Microbiología y Zoología AgrícolaFil: Francesena, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Centro de Estudios Parasitologicos y de Vectores. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios Parasitologicos y de Vectores; Argentina.Fil: Arneodo Larochette, Joel Demian. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Microbiología y Zoología Agrícola e Instituto de Biotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rocca, Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Centro de Estudios Parasitologicos y de Vectores. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios Parasitologicos y de Vectores; Argentina.Fil: Greco, Nancy Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Centro de Estudios Parasitologicos y de Vectores. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios Parasitologicos y de Vectores; Argentina. Provincia de Buenos Aires. Comisión de Investigaciones Científicas; Argentin

Temperature-Dependent Fecundity and Life Table of the Fennel Aphid <i>Hyadaphis foeniculi</i> (Passerini) (Hemiptera: Aphididae)

<div><p><i>Hyadaphis foeniculi</i> (Passerini) (Hemiptera: Aphididae) is a cosmopolitan species and the main pest of fennel in northeastern Brazil. Understanding the relationship between temperature variations and the population growth rates of <i>H</i>. <i>foeniculi</i> is essential to predict the population dynamics of this aphid in the fennel crop. The aim of this study was to measure the effect of constant temperature on the adult prereproductive period and the life table fertility parameters (infinitesimal increase ratio (<i>r_m</i>), gross reproduction rate (<i>GRR</i>), net reproduction rate (<i>R₀</i>), finite increase ratio (λ), generation time (<i>GT</i>), the time required for the population to double in the number of individuals (<i>DT</i>), and the reproduction value (<i>RV_x</i>)) of the fennel pest <i>H</i>. <i>foeniculi</i>. The values of lx (survival of nymphs at age <b>x</b>) increased as the temperature rose from 15 to 28°C and fell at 30°C, whereas mx (number of nymphs produced by each nymph of age <b>x</b>) increased from 15 to 25°C and fell at 28 and 30°C. The net reproduction rates (<i>R₀</i>) of populations of <i>H</i>. <i>foeniculi</i> increased with temperature and ranged from 1.9 at 15°C to 12.23 at 28°C for each generation. The highest population increase occurred with the apterous aphids at 28°C. The rate of population increase per unit time (<i>r_m</i>) (day) ranged from 0.0033 (15°C) to 0.1995 (28°C). The highest values of <i>r_m</i> were recorded at temperatures of 28°C and 30°C. The <i>r_m</i> values were a good fit to the models tested, with R² > 0.91 and R²_adj > 0.88. The models tested (Davidson, Sharpe and DeMichele modified by Schoolfield et al., Logan et al., Lamb, and Briere et al.) were very good fits for the <i>r_m</i> values observed, with R² > 0.91 and R²_adj > 0.88. The only exception was the Davidson model. Of the parameters studied, the reproductive capacity was higher in the apterous aphids, with the unique exception of daily fecundity at 28°C, which was higher in the alate aphids of <i>H</i>. <i>foeniculi</i>. Parameters relating to the age-specific fertility table for <i>H</i>. <i>foeniculi</i> were heavily influenced by temperature, with the highest biotic potential and population growth capacity found at 34°C. Therefore, the results obtained in this study could be of practical significance for predicting outbreaks of fennel aphids and improving the management of this aphid in fennel crops.</p></div