Impact of Nutritional Supplements on the Fitness of the Parasitoid Binodoxys communis (Gahan)

Alterative nutritional foods consumed by adult parasitoids play an important role in their fitness and ability to control pests because of food scarcity in many crops. While adult parasitoids feed on various sugars, they vary in their nutritional value for parasitoids. We assessed the effects of seven sugars (fructose, glucose, sucrose, trehalose, maltose, melezitose, and sorbitol) on the longevity, parasitism ability, parasitism behavior, and flight ability of B. communis, an important parasitoid of cotton aphids. We found that access to glucose, sucrose, or fructose, increased B. communis adult longevity more than the other sugars offered. All sugars except trehalose increased the parasitism rate to more than 50% compared to the starved control (only provided with water). We then compared parasitoid behaviors of wasps fed glucose, sucrose, or fructose to that of the starved control (with access only to water) and found that those fed B. communis spent more time either examining or attacking aphids than parasitoids in the control group, which spent more time walking or resting. Also, consumption of glucose, sucrose, or fructose also significantly improved the flight ability (the total flight distance, flight time, and average flight speed) of B. communis.

Host Preference and Fitness of Lysiphlebus testaceipes (Hymenoptera: Braconidae) in Different Instars of the Aphid Schizaphis graminum

Parasitoid fitness is strongly influenced by host quality for immature parasitoid development and by oviposition host choice patterns made by adult female parasitoids. This study aimed to determine immature host quality of Schizaphis graminum (Rondani) (Hemiptera: Aphididae) and Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae) host instars preference. To this end, the host quality of immature stages of S. graminum was assessed by rearing the parasitoid in all four instars of the aphid, placing each nymph stage of the aphid parasitized by L. testaceipes in separate Petri dishes with sorghum leaves over a 1% agar-water solution at 23 ± 1°C and a 12:12 h L:D photoperiod. The host-age preferences of the parasitoid between second and fourth instar nymphs were analyzed by choice (ten nymphs of each instar) and non-choice (ten nymphs of one instar) tests, observing parasitoid foraging in a 5-cm arena for 5 min under a stereoscopic microscope. Third and fourth instars were better hosts than first or second instars, with faster developmental times, resulting in larger wasps with bigger hind tibia size and more eggs in their ovarioles (i.e., higher initial egg load). Females preferred to oviposit in fourth instar aphids in both choice and non-choice tests. Selection by adult L. testaceipes females of older instars of S. graminum for oviposition maximizes parasitoid fitness as these instars are intrinsically more suitable for development of parasitoid offspring.

Rhizobacterial colonization of roots modulates plant volatile emission and enhances the attraction of a parasitoid wasp to host-infested plants

Beneficial root-associated microbes modify the physiological status of their host plants and affect direct and indirect plant defense against insect herbivores. While the effects of these microbes on direct plant defense against insect herbivores are well described, knowledge of the effect of the microbes on indirect plant defense against insect herbivores is still limited. In this study, we evaluate the role of the rhizobacterium Pseudomonas fluorescens WCS417r in indirect plant defense against the generalist leaf-chewing insect Mamestra brassicae through a combination of behavioral, chemical, and gene-transcriptional approaches. We show that rhizobacterial colonization of Arabidopsis thaliana roots results in an increased attraction of the parasitoid Microplitis mediator to caterpillar-infested plants. Volatile analysis revealed that rhizobacterial colonization suppressed the emission of the terpene (E)-α-bergamotene and the aromatics methyl salicylate and lilial in response to caterpillar feeding. Rhizobacterial colonization decreased the caterpillar-induced transcription of the terpene synthase genes TPS03 and TPS04. Rhizobacteria enhanced both the growth and the indirect defense of plants under caterpillar attack. This study shows that rhizobacteria have a high potential to enhance the biocontrol of leaf-chewing herbivores based on enhanced attraction of parasitoids.