Rhyzobius lophanthae Behavior is Influenced by Cycad Plant Age, Providing Odor Samples in a Y-tube Olfactometer

Abstract

The scale predator Rhyzobius lophanthae Blaisdell was introduced to Guam and Rota to control invasive Aulacaspis yasumatsui Takagi armored scale infestations on the native Cycas micronesica K.D. Hill populations. The predator demonstrated a clear preference for A. yasumatsui infesting adult plants, resulting in 100% seedling mortality due to the lack of a biocontrol of the scale on seedlings. A Y-tube olfactometer was employed to determine if scale-infested seedling leaves were less attractive to R. lophanthae than scale-infested mature tree leaves. Five paired combinations of seedling versus mature tree leaves were used. The R. lophanthae adults navigated toward scale-infested and un-infested leaves of adults and seedlings when paired with an empty chamber. However, a clear preference for adult leaves occurred when paired with seedling leaves. The results were unambiguous in charcoal-filtered air, intermediate in unfiltered air from an open laboratory, and most ambiguous when conducted with unfiltered in-situ air. The number of predators that did not make a choice was greatest for in-situ air and least for charcoal-filtered air. These results indicated that the substrate used in olfactometry influenced the results, and interpretations of charcoal-filtered air assays should be made with caution. Volatile chemical cues are involved in R. lophanthae preferring A. yasumatsui located on C. micronesica adults when infested adult and seedling leaves are present.

Biotic Threats to Cycas micronesica Continue to Expand to Complicate Conservation Decisions

“…Second, the predator tends to avoid the plants’ lowest stratum for unknown reasons such that A. yasumatsui infestations are uncontrolled on leaf, stem, and root surfaces near the ground [ 41 ]. Third, the olfactory signals from A. yasumatsui are less attractive to the predator when the infested leaves are from seedlings rather than adults [ 42 ]. These and other phenomena have limited this predator’s success in protecting the tree host from A. yasumatsui damage.…”

Olfactometric response of selected crop pests to the scent of common nettle (Urtica dioica L.) and the influence of aqueous plant extracts on their behavior

“…Entomological studies using an olfactometer were conducted according to the methodology described in the works of Islam et al (2017) and Zhang et al (2022). The utility of such olfactometers for assessing insects' olfactory preferences has been established in various studies (Ninkovic et al 2013;Marler and Marler 2018;Masui et al 2020;Mensah-Bonsu et al 2020). The Y-tube olfactometer consisted of one incoming arm and two testing arms, each comprising glass tubes with dimensions of 250 mm in length and 12 mm in diameter.…”

Aulacaspis yasumatsui Delivers a Blow to International Cycad Horticulture

“…This predator behavior may result in localized A. yasumatsui infestations on leaves near the soil surface on plants that exhibit no A. yasumatsui on leaves in the higher strata. Finally, when provided a binary choice in an olfactometer assay, this predator prefers A. yasumatsui on mature tree leaves versus seedling leaves [94].…”