Project Overview

Reports

Commodities

Target Pests

Practices

The three goals of this project are to delineate the current field distribution of the puncturevine biological control agents Microlarinus lareynii and Microlarinus lypriformis, to compare the current cold hardiness limits of the Microlarinus weevil populations, and finally to determine the potential phenotypic plasticity of Microlarinus weevils in the western United States.  We will use field surveys to establish the current northern limit of Microlarinus weevils. During this regional survey, we will also collect weevils from across the climatic gradient of puncturevine populations. Using these field collected weevils, we will establish the cold tolerance threshold in laboratory experiments and test overwintering survival in field trials at three different latitudes from Colorado to southern New Mexico.

A systematic survey will improve our understanding about where weevil populations are successful as well as reveal any previously unknown populations of weevils. Defining the quantitative cold hardiness limits of known populations of Microlarinus will provide a baseline for comparison to additional populations of Microlarinus across a latitudinal gradient in the western United States. This research will provide the foundation for improved classical biological control of puncturevine in one of two ways. If there are differences in cold hardiness among Microlarinus populations, then refining distribution strategies to match weevils to climate will be more a cost-effective management strategy (Morin et al. 2009). This result would also suggest that weevils have enough plasticity to adapt to cold environments and it may be possible to develop more cold hardy weevils. Alternatively, if there are no differences in cold tolerance, then sourcing weevils from a wider climatic range (e.g. using weevils from southern New Mexico to control Colorado populations of puncturevine) would increase the supply of available weevils.

The success of puncturevine biological control is considered variable, largely due to the better weevil establishment in the warmer parts of the western region. Generally, the success of a biocontrol programs is strongly dependent on the ability of the biological control agent to build up large populations across the geographic range of the target weed (Litto et al. 2021). This project initiation proposal relates directly to the goal of the Western IPM Center by enhancing the biological control of puncturevine, a western region-wide invasive weed. Currently, puncturevine biological control is limited by the availability of puncturevine weevils (D. Bean, pers. comm.) Improved establishment of Microlarinus across a wider geographic region in the west would improve biological control of puncturevine.  

1. Delineate the current introduced range of Microlarinus in the western US by conducting a region-wide survey of Tribulus and Microlarinus in New Mexico and Colorado.
2. Establish the laboratory cold tolerance and thermal minima for adult stages of M. lareynii and lypriformis populations from across a latitudinal gradient.
3. Test if acclimatization of southern Microlarinus could lower their thermal minima and improve their cold tolerance.
4. Test differences in field overwintering survival between Microlarinus species and among Microlarinus populations across a latitudinal gradient of puncturevine populations.