Insect Note #26 (Revised)

Prepared by:
K. A. Sorensen, Extension Entomologist

Dated 4/94
Placed on the Web 4/95 by the Department of Entomology, NCSU

Mexican Bean Beetle

Epilachna varivestis Mulsant. Coleoptera: Coccinellidae

The Mexican bean beetle, the most injurious pest of beans has been less numerous in recent years. Both adults and larvae feed on the leaves. When abundant, they also attack pods and stems. Death of heavily infested plants usually results.

Biology

Adult beetles overwinter in hedge rows, ditch banks and woodlands and may attack plants soon after seedlings emerge. Most beetles leave their winter quarters over a 20-month period. Following feeding, adult females deposit eggs on the underside surface of leaves. Eggs hatch in 5 to 14 days and larvae continue to feed for 2 to 5 weeks. Larvae pupate on the leaves and adults emerge after about 10 days. Adults feed, mate and lay eggs over a period of 2 weeks. Generation time from egg to adult is about 30 days. In North Carolina, there are 3 to 4 generations each year.

Description

Adult - Adult beetles are convex in shape, about 1/3 inch in length and vary from yellow to coppery-brown in color. Each wing cover has 8 small, black spots.

Eggs - Eggs are about 1/20 inch in length, orange-yellow in color and are fastened in groups of 40 or more to the underside of leaves.

Larvae - Full grown larvae are 1/3 inch in length, oval in shape, yellow in color and have 6 rows of branching, black-tipped spines on their backs.

Pupa - The exposed pupa is smooth, yellow-orange in color, rounded in front and is attached to the underside of host leaves.

Host Plants

Mexican bean beetles have a wide host range. They are most commonly encountered on garden and field beans and cowpeas. Soybean, clover, alfalfa and related weeds may also be attacked.

Damage

Both larvae and adults feed on the leaves, leaving the upper surface intact. Damaged plants have a characteristic lacelike (skeletonized) appearance. Pods and stems are often attacked and the shredded plants may die before any crop is matured.

Distribution

The Mexican bean beetle was at first limited from Colorado southward. It is now common throughout the United States with the exception of the Pacific Coast states.

Control

Since damage is usually most severe during July and August, very early maturing bean varieties and fall plantings may be grown with little injury. Prompt removal of pods and destruction of old plants are suggested as insurance against population buildup. An extensive parasite release program in the DELMARVA Peninsula in the late 70's has resulted in extremely low populations of Mexican bean beetle in this area and into North Carolina. Chemical control consists of applying foliar insecticides to the underside of leaves or using a granular insecticide in furrow at planting.

Commercial Plants:
Insecticide and Formulation Amt. of Formulation per Acre Minimum Interval (Days) to Harvest Comments
       
acephate (Orthene) 75S 2-3lb 14 Lima beans may be treated and harvested the same day.

carbaryl (Sevin)

50SP
80SP
4XLR
1-2lb
5/6 to 1/4lb
1qt		 0
0		  
bifenthrin (Capture) 2EC 6.4oz 3  
dimethoate (Cygon) 4EC 1pt 0 Apply in furrow below seed at planting. Avoid contact with seed. Make 1 application.
disuloton (DiSyston)* 15G 6-12oz/1000 ft row 60  
phorate (Thimet) 15G 6-12oz/1000 ft row 60  
esfenvalerate (Asana XL) 0.66 4.8-9.6oz 3 Do not exceed 0.8lb a.i per acre per season. Do not feed treated plants to livestock. 

 
*Some control of aphids, bean leaf beetle, potato leafhopper and thrips will be obtained with preplant applications.

Home Gardens:

Use carbaryl (Sevin) 80WP at 1/2 tablespoons per gallon of water, or dust with carbaryl (Sevin) 5% dust. Sevin also controls bean leaf beetles. There is no waiting period with Sevin on beans. Sevin will not control aphids. Consider using Pyrellin EC at 1 to 2 teaspoons per gallon of water in an organic setting.

The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsements by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. All pesticide recommendations provided in this publication apply to pest control in North Carolina. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain information about product usage in your locale and examine a current product label before applying any chemical. The information presented on pest biology is based on conditions in North Carolina and may not be applicable to your locale. For further information, we recommend that you contact the Cooperative Extension Service office in your county.