Host-Parasitoid Interactions in Santa Barbara Co., CA

For more information please visit my research website: Plant Bug Central

I investigate how environmental variation influences species persistence in a host – parasitoid community inhabiting the coastal sage scrub in Santa Barbara Co., CA, USA. The community consists of the bordered plant bug [Largus californicus] (Image 1), a herbivore on bush lupine [Lupinus arboreus] (Image 2). The plant bug is attacked by three parasitoid species: an egg parasitoid [Gryon largi] as well as a parasitoid wasp [unidentified sp.] and a tachinid fly [Trichopoda pennipes] that attack nymphal and adult stages (Image 3).

 This research is motivated by a striking pattern in the host’s population dynamics. In many Hemiptera (true bugs), adults exhibit more stable dynamics than eggs and nymphs because of invulnerability to attack by natural enemies and because fluctuations due to seasonal temperature variation are attenuated due to stage structure. The bordered plant bug provides an exception to this pattern: adults are vulnerable to attack by natural enemies and exhibit high variability in abundance.

I hypothesize that it is the interplay between the bug’s sensitivity to temperature-variation and attack by enemies at multiple life-stages that drives its population dynamics. I test these mechanisms using a combination of mathematical models, fieldwork, and laboratory experiments in temperature-controlled incubators and using an automated video system (Image 4).

A model parameterized with data from laboratory experiments predicts that host population dynamics exhibit long-term oscillations in abundance even in a constant-temperature environment. These oscillations arise due to a developmental time-delay and are stabilized by intra-specific competition within the adult life-stage that causes fecundity to decline with increasing adult abundance.

I investigate bug population dynamics under ambient seasonal variation by quantifying the temperature responses of life history traits in laboratory experiments and incorporating these responses into the dynamical model. The temperature responses of key life history traits are determined by rearing bugs in constant-temperature incubators. Preliminary data fit theoretical predictions well and suggest that temperature variation influences population dynamics in the field.

I use an automated video system to investigate host-parasitoid interactions, focusing on behavioral traits such as searching efficiency and handling time that are crucial to understanding host-parasitoid dynamics. Integrating this work with temperature-response data facilitates a better understanding of how the interplay between species interactions and environmental variation influences population persistence and species coexistence. This research has practical applications for the conservation of biodiversity in the face of climate change and biological control of  agricultural and invasive pest species.