Not Led by the Nose: Volatiles from Undamaged Eucalyptus Hosts Do Not Influence Psyllid Orientation

Psyllids (Hemiptera: Psylloidea) are small sucking insects with high host plant specificity. Despite the primitive olfactory system of psyllids, some species have been suggested to rely on host plant volatiles (HPVs) for seasonal migration between summer deciduous hosts and winter coniferous hosts. Similarly, enhanced attraction of psyllid vectors has been observed as a result of the manipulation of host odors by plant pathogens. As yet, there are no studies of olfaction in psyllids that utilize evergreen eucalypt hosts. We investigated the behavioral responses of adults of four Eucalyptus-feeding psyllids—Ctenarytaina eucalypti, C. bipartita, Anoeconeossa bundoorensis and Glycaspis brimblecombei—to their respective HPVs in Y-tube olfactometer bioassays. We also used existing physiological data for C. eucalypti to investigate potential olfactory tuning that may modulate the preference for morphologically juvenile leaves over morphologically adult leaves. Although adult C. eucalypti were consistently repelled by HPVs from damaged host leaves, none of the species exhibited positive chemotaxis to HPVs from undamaged leaves. Surprisingly, G. brimblecombei was repelled by HPVs from undamaged host leaves. Our findings provide little support for a significant role of olfaction in host location by Eucalyptus-feeding psyllids. We propose a number of ecological hypotheses to explain these unexpected findings.

Cues Triggering Mating and Host-Seeking Behavior in the Aphid Parasitoid Aphidius colemani (Hymenoptera: Braconidae: Aphidiinae): Implications for Biological Control

Aphidius colemani Viereck (Hymenoptera: Braconidae: Aphidiinae) is a pan-tropical, broadly oligophagous, solitary endoparasitoid of many aphids of economic importance. Here, we review current knowledge about this important biological control agent, with a special focus on the physical and chemical cues triggering mating and host-seeking behavior. First, we focus on female-borne olfactory cues evoking courtship in A. colemani males, as well as on the relationship between male mating performance and quality of the host species. Second, we examine how A. colemani females forage for hosts and assess their suitability, using both aphid-borne kairomones and host-related physical cues. Third, we review A. colemani-based biological control approaches, outlining how knowledge of its reproductive behavioral ecology may enhance biological control of aphid pests. Concepts for future biocontrol programs are outlined, including 1) use of sex attractant dispensers for monitoring, 2) mass-rearing optimization based on knowledge of mate-finding strategies and sexually selected traits, 3) deployment of aphid-borne foraging kairomones as field lures to attract parasitoids into infested agro-ecosystems, 4) use of sensitization or associative learning practices to optimize efficacy of mass-reared wasps.