Mexican bean beetles have invaded the Snoqualmie Valley

[Larry Fisher]

Mexican bean beetles have invaded the Snoqualmie Valley. At least 3 Trellis members, including me - I found 3 on my string beans, reported seeing them last year. That's the bad news; the good news is that the MBBs have been back east for decades and so there is lots of ready info on them, including in books on pests.

The Mexican bean beetle, Epilachna varivestis, is a species of lady beetle which is a notorious agricultural pest. The Mexican Bean Beetle feeds on leaves, pods and stems as both larvae and adult.

 

from www.organicgardeninfo.com/mexican-bean-beetle.html :

Common names: Mexican Bean Beetle
Scientific name: Epilachna varivestis
Region: This beetle is found in eastern United States and parts of Texas, Arizona, Colorado, and Utah.  Similar species can be found throughout North America.

Life cycle: One to three generations are produced each year.  The adults hibernate in open fields, woods, garden rubbish, or weeds.  It will return late in March in the South and in June in the northern United States.  Two weeks latter, it deposits its yellow clusters of eggs on the undersides of leaves.

Physical Description: This 1/4 inch, round insect is yellowish brown with 16 black spots on its wing covers.  Its eggs are yellow and are laid in clusters on underside of leaves, while the spined, 1/3 inch long larva is orange.

Feeding characteristics: This ravenous beetle feeds on leaves, pods and stems as both larvae and adult.  It carries the reputation of being the number one enemy of vegetable gardeners in the east.  The beetle will skeletonize leaves from underneath.  It will eat any garden bean, but prefers the lima bean.

Controls: The organic gardener's first line of defense is handpicking.  Drop the beetle in a bucket of water.  When harvest is over, clean your garden of all debris.  This will reduce overwintering areas.

Try planting your bean crop early, some success has been accomplished by this strategy.  You can also interplant with potato, nasturtium, savory, and garlic.  Some gardeners have even had success with a spray consisting of crushed turnips and corn oil.  Alternatively, try a cedar spray, from boiled cedar chips in water.  You can use Rotenone or pyrethrum for more serious infestations.

This beetle does have predators.  Some species of Lady Beetles will prey on the eggs on larvae.  Another useful insect is the Spined Soldier Beetle, which will attack all life stages of the Mexican Bean Beetle.

A bean beetle parasite, Pediobius foveolatus, is now on the market.  The tiny wasp will lay its eggs in the beetle larvae.  Several varieties of bean have been known to show signs of resistance.  These beans are the Wade, Logan, and Black Valentine.  Beans susceptible are the State, Bountiful, and Dwarf Horticultural varieties.

[David Bach]

Yes, we have seen these guys for over a year, both in our Fall City garden and out by the river in another garden area. Even without suitable crops the beetles seemed to be quite numerous just northwest of Fall City out by the river where we and others are growing. We had some problems with them even when we could identify only a few. Larger numbers could easily decimate a planting.

I talked with WSU extension about this in January and they didn't know MBBs were here. This is a quote:

"I'm wondering about the Mexican bean beetle. As far as I know it hasn't been found here either. It is a renegae ladybug, the only, or one of a very few, that feed on plants. The rest are predators. I am hearing of the spotted cucumber beetle damaging plants in the Tualco Valley and it may well be in Snoqualamie V. as well."

So, it is a good idea to let them know. I talked with Sharon Collman at [e-mail].

The best protection I've read about is to examine the underside of leaves and scrape off the yellow eggs (yeah, that was a lot of fun!). We didn't find many in our Fall City garden and the beetles still did a good bit of damage.

[David Bach]

Margaret suggests that another preventive is to cover the plants with insect barrier/floating row covers to keep the beetles away from the plants. By the way, she also says that the beetles are as happy with cruciferous vegetables (Brassicaceae), which is a big family of popular veggies, as with beans.

It makes sense to me that if you have beetles you'll have the eggs under leaves. And that once those eggs hatch the larvae will munch also. 

So by the time you see skeletonized leaves, the process is well underway, possibly into later generations. 

And, the critters are already in the fields along the river.