It has been a while since I've posted. We have been quite busy in the lab with a long list of projects as well as some laboratory renovation preparations. It has been a while since
I've posted on our progress toward finding resistance to Mexican bean beetles in dry edible beans. We have made a lot of progress. We have tested beetle populations for two, presumably, divergent beetle populations and have found that certain varieties of pinto beans (and a couple other market classes) yield significantly lighter beetle larvae. The mass of an insect's larval stage over a measured period of time has been used in many bioassays as a measure for host suitability. Over a side-by-side comparison of treatments (different dry bean varieties in this case) we can measure the gain in larval mass over a set number of days and compare those weights across treatments. Lighter larvae are then assumed to be less fit and presumably (if the experiment is designed properly) there is some characteristic of the plant that caused the larvae from one variety to weigh less than another. As
illustrated here, our bioassays to date have used a "detatched leaf method". This method allows us to test a large number of varieties at once. However, some plant defense compounds are known to be affected by different kinds of plant injury and some kinds of injury actually stimulate a delayed response that travels throughout the plant. Since we cut away the leaf material from the plant in our bioassays, we could be interfering with some important plant resistance mechanisms that may be expressed differently when you remove tissue from a plant. So the image on this page shows another kind of bioassay that we have just begun. In this bioassay we have designed small cages to contain the Mexican bean beetle larvae on leaves that are still attached to the plant. We are using the same varieties that we think represent the extremes of susceptibility and resistance to the beetles. We hope that this bioassay will agree with our cut-leaf bioassay, but we won't know for a few more days. Stay tuned for more....
