Indian Bt cotton varieties do not affect the performance of cotton aphids.

Cotton varieties expressing Cry proteins derived from the soil bacterium Bacillus thuringiensis (Bt) are grown worldwide for the management of pest Lepidoptera. To prevent non-target pest outbreaks and to retain the biological control function provided by predators and parasitoids, the potential risk that Bt crops may pose to non-target arthropods is addressed prior to their commercialization. Aphids play an important role in agricultural systems since they serve as prey or host to a number of predators and parasitoids and their honeydew is an important energy source for several arthropods. To explore possible indirect effects of Bt crops we here examined the impact of Bt cotton on aphids and their honeydew. In climate chambers we assessed the performance of cotton aphids, Aphis gossypii Glover (Hemiptera: Aphididae) when grown on three Indian Bt (Cry1Ac) cotton varieties (MECH 12, MECH 162, MECH 184) and their non-transformed near isolines. Furthermore, we examined whether aphids pick up the Bt protein and analyzed the sugar composition of aphid honeydew to evaluate its suitability for honeydew-feeders. Plant transformation did not have any influence on aphid performance. However, some variation was observed among the three cotton varieties which might partly be explained by the variation in trichome density. None of the aphid samples contained Bt protein. As a consequence, natural enemies that feed on aphids are not exposed to the Cry protein. A significant difference in the sugar composition of aphid honeydew was detected among cotton varieties as well as between transformed and non-transformed plants. However, it is questionable if this variation is of ecological relevance, especially as honeydew is not the only sugar source parasitoids feed on in cotton fields. Our study allows the conclusion that Bt cotton poses a negligible risk for aphid antagonists and that aphids should remain under natural control in Bt cotton fields

Editorial: Ecosystem Services and Disservices Provided by Plant-Feeding Predatory Arthropods

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Perception of Chromatic Cues During Host Location by the Pupal Parasitoid Pimpla turionellae (L.) (Hymenoptera: Ichneumonidae)

Chromatic and achromatic plant cues are expected to be particularly important for parasitoids of endophytic pupal hosts, because these stages do not feed and therefore avoid volatile emission caused by plant tissue damage. Endophytic feeding can cause discoloration or desiccation, leading to changes in color and/or brightness of infested plant parts that may be visually detected by parasitoids. The role of color cues in the host-finding behavior of parasitoids is poorly understood, and the visual system of most parasitoid species has not yet been investigated. We studied color discrimination ability and innate color preferences in the pupal parasitoid Pimpla turionellae (L.) (Hymenoptera: Ichneumonidae) during location of concealed hosts. Responses to combinations of yellow and blue bands of different reflectance intensities were investigated on cylindrical models of plant stems. The parasitoid's reaction to these chromatic cues was evaluated by scoring the number of ovipositor insertions into the colored bands. Female parasitoids discriminated blue from yellow irrespective of total reflectance and inserted their ovipositors significantly more often into the blue area. True color vision is demonstrated for the examined species, and responses to chromatic cues are discussed in relation to their importance for host location in parasitoids. Results of this study and of our previous work suggest that P. turionellae uses contrasts (chromatic or achromatic) rather than specific color characteristics in visual host locatio

Effects of vegetation management in field margins on Meteorus autographae and Pseudoplusia includens.

We investigated whether the age of field margins that had been established for conservation of northern bobwhite populations also enhance biological pest control in adjacent cotton fields. The impact of second year margins on the cotton crop did not significantly differ from first year margins with regard to pests or biological control. Analysis of the gut contents of M. autographae, suggested that this species is food-limited in the margins, whereas a single vetch species proved to be a good food source. This study shows that non-crop structures designed for a particular ecological function may be unsuitable for other ecological services. By making small adjustments in the vegetative com posit ion, we might be able to effectively stack multiple ecological functions and thereby optimize ecological benefits

Bloemrijke akkerranden voeden natuurlijke vijanden.

Veel natuurlijke vijanden van plaaginsecten hebben, vooral wanneer ze vleugels hebben, stuifmeel of nectar nodig. Bloemrijke akkerranden kunnen het gebrek hieraan in ons moderne agrarische landschap deels opheffen. Lang niet alle bloem(mengsels) zijn echter geschikt als ‘wegrestaurant’. Om door parasitoïden en predatoren benut te worden, moeten deze de nectar en stuifmeel kunnen vinden, moeten ze er goed bij kunnen en door andere insecten worden opgegeten. Wil het stimuleren van natuurlijke vijanden vervolgens ook leiden tot een betere plaagbestrijding op de akker, dan zal het mengsel op tijd moeten bloeien en niet ook de plaag moeten stimuleren. Dit betekent dat alleen met voldoende kennis over ecologie van plaag en natuurlijke vijand akkerranden kunnen worden samengesteld, die optimaal de natuurlijke plaagbestrijding zullen aanjage