Mexican bean beetle
Epilachna varivestis
A copper ladybird lookalike — and the one member of the family that eats plants, skeletonizing bean leaves from below. Learn the sixteen spots before you spare it.
How to know it
A domed beetle 7 mm long, coppery-tan rather than red, with sixteen black spots in three rows across the wing cases. The larva is unmistakable: a fat yellow grub covered in branching black-tipped spines, feeding on the leaf underside. Both are on beans, which is where a true ladybird rarely settles to feed.
What you'll see
- Leaves skeletonized from beneath into a lace of veins, leaving a thin papery upper surface.
- Yellow spiny grubs in loose groups on the leaf undersides.
- Clusters of upright yellow eggs, 40 or more, glued to the underside of a leaf.
- Pods scarred and stems chewed once the leaves are gone.
- Copper-colored beetles that keep to the underside of the foliage rather than sunning themselves openly.
Where it comes from
Adults overwinter in leaf litter, hedgerows and field edges and move into beans in early summer. Two to three generations a year, each taking about a month; the last one produces the beetles that go into winter. The population climbs sharply through the season, so a light first generation is a warning rather than a reprieve.
Mid-Atlantic and eastern gardens carry the heaviest pressure, and snap beans and limas grown in the same place year after year the worst of all. Hot summers speed the generations along.
Dealing with it
- Crush the yellow egg clusters and the spiny larvae by hand twice a week; ten minutes a week early beats anything later.
- Spray insecticidal soap or neem on the leaf undersides while the larvae are small.
- Pull the crop as soon as the harvest is finished rather than leaving a nursery for the last generation.
- Release the parasitic wasp Pediobius foveolatus where it is available; it is a well-proven answer in the mid-Atlantic.
- Check before you squash — a true ladybird larva is dark and alligator-shaped, and eats aphids.
Keeping it out
- Sow early and grow a fast bush cultivar so the crop is picked before the second generation builds.
- Rotate beans well away from last year row, and clear all bean debris in autumn.
- Cover young plants with mesh until they flower.
- Interplant with rosemary, savory or marigold, and keep nectar flowers nearby for the parasitoids.
- Grow a trap row of an early snap bean, then pull and destroy it with the beetles on it.
What it goes for
Snap, lima, pole and dry beans, plus cowpeas and soybeans.
Who hunts it for you
- Assassin bugReduviidae A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be. Grow to recruit it: Dill,Fennel,Goldenrod,Sweet alyssum,Tansy,Yarrow
- Parasitic waspsBraconidae & Trichogramma Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled. Grow to recruit it: Cilantro,Dill,Fennel,Lovage,Parsley,Sweet alyssum
- Spined soldier bugPodisus maculiventris A predatory stink bug — same shield outline as the pest, but with a sharp spine at each shoulder and a beak it uses to spear caterpillars and beetle grubs. Learn the spines before you squash a shield bug, because this one is on your side. Grow to recruit it: Dill,Fennel,Sweet alyssum,Yarrow
- Tachinid flyTachinidae Bristly, house-fly-lookalike parasitoids that lay eggs on caterpillars, beetle grubs, and earwigs — the maggot consumes the host from within. Adults sip nectar from shallow umbels and daisies. Grow to recruit it: Cilantro,Dill,Feverfew,Parsley,Sweet alyssum
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com