Organic mulch can increase the survival of a weed biological control agent during laboratory mass rearing

Authors: Halbritter, Dale; Wheeler, Gregory

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2019
Publication Date: 4/22/2019
Citation: Halbritter, D.A., Wheeler, G.S. 2019. Organic mulch can increase the survival of a weed biological control agent during laboratory mass rearing. Biocontrol Science and Technology. 29(9):852-859. https://doi.org/10.1080/09583157.2019.1608510.
DOI: https://doi.org/10.1080/09583157.2019.1608510

Interpretive Summary: Raising large numbers of organisms is a critical component to classical biological control programs. The needs of each life stage should be met to ensure the greatest survival. We investigated a method to improve pupal survival of the thrips Pseudophilothrips ichini, a proposed biological control agent of the highly invasive Brazilian peppertree, Schinus terebinthifolia. Specifically, we tested the effect of organic mulch on the number of adults emerging. Either compressed coconut fiber, dried Brazilian peppertree leaves, or dried sphagnum moss were added to the soil surface of potted Brazilian peppertrees. Nothing was added to control plants. Each plant was sealed in a clear acrylic cylinder and 50 thrips larvae were added. The number of adults emerging were compared between mulch treatments. The greatest number of adults emerged from plants with sphagnum moss, with no differences among the other mulches and the control. We confirm the majority of thrips are pupating in the moss rather than in the soil. Relative humidity was higher in the mulch layers compared to the plant canopy. Sphagnum moss likely provided the most ideal hiding places for larvae and the higher humidity reduced the chances of pupae drying out. We discuss the use of organic mulches in natural settings and emphasize the benefits of organic mulch to insects with soil-dwelling life stages raised in a laboratory environment.

Technical Abstract: Mass rearing agent organisms is a critical component to classical biological control programs. Maximizing survival of each life stage necessitates ideal, stage-specific conditions are available in the rearing protocol. We investigated a method to improve pupal survival of Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae), a proposed biological control agent of the highly invasive Brazilian peppertree, Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae). Specifically, we tested the effect of organic mulch on the number of adults emerging. Either compressed coconut fiber, dried Brazilian peppertree leaves, or dried sphagnum moss were added to the soil surface of potted Brazilian peppertrees. Nothing was added to control plants. Each plant was sealed in a clear acrylic cylinder and 50 second instar thrips were added. The number of adults emerging were compared between mulch treatments. The greatest number of adults emerged from plants with sphagnum moss, with no differences among the other mulches and the control. We confirm the majority of thrips are pupating in the moss rather than in the soil. Relative humidity was higher in the mulch layers compared to the plant canopy. Sphagnum moss likely provided the most ideal harborages for thigmotactic larvae and the humid microhabitat minimized desiccation. We discuss the use of organic mulches in ecological contexts and emphasize the benefits of organic mulch in captive rearing operations that involve insects with soil-dwelling stages.