Large Milkweed Bug

Overview

The large milkweed bug, Oncopeltus fasciatus, is a true bug (Hemiptera) and common insect found on milkweed plants (Asclepias spp.), identified by its vibrant orange and black coloration. Adults have three distinct black patches surrounded by orange: Two diamond-shaped patches on the pronotum (directly behind the head) and on the forewings, and a wide black band in the middle. Nymphs are a darker red-orange color, with black wing buds. As a piercing-sucking insect, it uses its long proboscis to feed on the seeds of milkweed plants. They are typically found clustered in small groups on the stems, leaves and fruit. The bodies of milkweed bugs contain toxic compounds derived from the sap which they suck from milkweed, making them unpalatable to predators.  

Symptoms and Diagnosis

Milkweed bugs are more of a nuisance than a threat to milkweed plants. They feed on the seeds by piercing the seed pod and can be found in all stages of growth on the plants in mid to late summer.

Life Cycle

The milkweed bug undergoes incomplete metamorphosis. Eggs are a light lemon yellow, changing to a reddish color. The incubation period is about four to five days. Nymphs look similar to adults, but have a different color pattern and underdeveloped wings, which appear early in their development. They will go through five instars before they reach adulthood, with each molt lasing five to six days. An adult will live for about one month. The insect overwinters as an adult.

Integrated Pest Management Strategies

1. Live with the insect. Milkweed bugs are not a major threat to milkweed plants, as they do little damage and are only present for a short period of time. Treatment or removal is typically not needed. 

2. Remove insects. If needed, light infestations can be controlled by handpicking them from plants. 

3. Sanitation. Remove leaf litter and spent stalks in the fall to eliminate overwintering sites.

4. Use insecticidal soap. Insecticidal soaps can be effective in managing insects on plants. 

5. Use chemical insecticides. If necessary, chemical insecticides can be used, but should only be considered as a last resort. Use caution when selecting insecticides as some may be harmful to beneficial insects.

Organic Strategies

Strategies 1 - 3 are strictly organic approaches. For an organic approach to Strategy 4, consult the Organic Materials Review Institute (OMRI™) for appropriate insecticidal soap products.

Pesticide Disclaimer: 

Always follow the product's label and ensure the product is effective against milkweed bugs. Not following the pesticide label before usage is a violation of federal law.