Using Chemical Ecology to Enhance Weed Biological Control

Abstract

In agricultural systems, chemical ecology and the use of semiochemicals have become critical components of integrated pest management. The categories of semiochemicals that have been used include sex pheromones, aggregation pheromones, and plant volatile compounds used as attractants as well as repellents. In contrast, semiochemicals are rarely utilized for management of insects used in weed biological control. Here, we advocate for the benefit of chemical ecology principles in the implementation of weed biocontrol by describing successful utilization of semiochemicals for release, monitoring and manipulation of weed biocontrol agent populations. The potential for more widespread adoption and successful implementation of semiochemicals justifies multidisciplinary collaborations and increased research on how semiochemicals and chemical ecology can enhance weed biocontrol programs.

Keywords: GC-EAD; aggregation pheromone; biological control implementation; semiochemical.

Figure 1

An example of the output of gas chromatographic-electroantennagraphic detection (GC-EAD) of volatiles from feeding D. carinulata adult males [15]. This shows the electrophysiological response of an isolated insect antenna (lower line, in black) to GC fractionated volatile compounds collected from feeding adults of D. carinulata (upper line, in pink), enabling researchers to isolate compounds that are antennally active (e.g., the D. carinulata pheromone blend, compounds A&B, (2E,4Z)-2,4-heptadienal and (2E,4Z)-2,4- heptadien-1-ol, respectively, which were fractionated from the volatiles mixture). Figure reproduced with permission from [15], copyright 2005 SpringerNature.

Figure 2

(A) Aggregation of Diorhabda carinulata on Tamarix. (B) A field release of D. carinulata from a cardboard container, typical for insect biocontrol releases.

Figure 3

Yellow sticky cards baited with the antennally active compounds, D. carinulata pheromone blend + green leaf volatiles, as part of a field trial conducted in western Nevada on 5 April 2004. Attraction of adult beetles to the cards was the measure of semiochemical activity of the volatile compounds. Allard Cossé, chemical ecologist with the USDA ARS, is here seen checking the trap as part of a cooperative effort between USDA ARS chemists and biocontrol practitioners [15,16].

Figure 4

Schematic representation of dispersing D. carinulata adults moving out of defoliated areas and seeking green tamarisk for feeding and oviposition (reproductive state) or simply feeding (diapause destined state).

Figure 5

A push-pull semiochemical strategy to repel reproductive adult D. carinulata away from nesting territories of the endangered southwestern willow flycatcher, where tamarisk may be utilized [43] and attract them to areas where tamarisk is targeted for removal. The repellent (red triangles) is placed near nesting territories where it diminishes the number of adult beetles colonizing tamarisk shrubs [17]. The D. carinulata pheromone blend (blue triangles) is placed on trees targeted for removal. Beetles are attracted (black arrows) to the pheromone, resulting in elevated D. carinulata populations and accelerated defoliation of the shrubs [23,54]. Targeted areas with blue triangles will be defoliated early in the season while the flycatcher nesting territory will remain green until later, after birds have fledged.