Watch for Blister Beetles in Alfalfa

Striped blister beetle adult feeding on leaves.
( Adam Varenhorst, South Dakota State University Extension )

We are receiving several reports of blister beetles in South Dakota. While the larvae of these insects are considered beneficial due feeding on grasshopper eggs, the adults can cause defoliation as well as health issues for livestock. Blister beetle populations will typically follow areas that had large grasshopper populations during the previous growing season. Defoliation caused by blister beetle adults is usually minor. However, the main concern with these insects is that the adults contain a chemical known as cantharidin that is capable of producing painful blisters. Cantharidin is present in blister beetle hemolymph (blood) but can be exuded through reflexive bleeding when pressure is applied to the beetle. This chemical can prove fatal when ingested in large quantities by livestock, especially horses, due to the irritation it causes in the gastrointestinal and urinary tracts of the animals.

Although there are several species of blister beetles found in South Dakota, they vary in their toxicity to livestock and their ability to defoliate crops (Table 1). The three-striped blister beetle contains a higher concentration of canthardin, while the margined blister beetle is noted for having the greatest potential to cause severe defoliation.

Table 1. Relative blister beetle toxicity to horses.

Species Estimated number of blister beetles required to cause mortality by horse weight
  275 lbs 500 lbs 825 lbs
Black blister beetle 175 1,100 1,700
Three-striped blister beetle 40 80 120

*Adapted from Capinera et al. 1985. J. Econ. Entomol. 78: 1052-1055.

Identification

As their name implies, striped blister beetles have black stripes that run the length of their yellow/orange abdomens. Striped blister beetles have an orange head with two oval markings that are separated by an orange line. The thorax, which is narrower than both the head and abdomen, is grey with two black lines on it. They have black antennae and gray/black legs. All blister beetles have elytra that are soft, and generally do not cover the end of their abdomen (Figure 2).

Elongate beetle with black and orange stripes on elytra and orange head with two black markings.
Figure 2. Striped blister beetle adult. Courtesy: Adam Varenhorst

Management Recommendations

If blister beetles are present in alfalfa prior to cutting, there are a few options for reducing the risk of livestock poisoning. The first option is to cut the hay without using a conditioner. Since the chemical is released when the beetles are crushed, hay conditioners can actually increase the amount of canthardin present in the hay. In addition, allowing the hay to dry completely after cutting gives adults an opportunity to crawl away prior to raking and baling.

Insecticides can also be applied to reduce blister beetle populations. However, when the insects are sprayed, they often clutch onto plants and may still be present in the hay at the time of harvest.

Comments

Restricted HTML

  • Allowed HTML tags: <a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd> <h2 id> <h3 id> <h4 id> <h5 id> <h6 id>
  • Lines and paragraphs break automatically.
  • Web page addresses and email addresses turn into links automatically.
6 + 12 =
Solve this simple math problem and enter the result. E.g. for 1+3, enter 4.
Submitted by Olivia Hannah on Wed, 07/11/2018 - 18:01

Hi everyone I'm Olivia Hannah and am here to share the wonderful work Dr Raypower did for me. After 5 years in marriage with my husband with 2 kids, my husband started acting weird and going out with other ladies and showed me cold love, on several occasions he threatens to divorce me if I dare question him about his affair with other ladies, I was totally devastated and confused until a old friend of mine told me about a spell caster on the internet called Dr. Raypower who help people with relationship and marriage problem by the powers of love spells, at first I doubted if such thing ever exists but decided to give it a try, when I contact him, he helped me cast a love spell and within 48hours my husband came back to me and started apologizing, now he has stopped going out with other ladies and his with me for good and for real. Contact this great love spell caster for your relationship or marriage problem to be solved today via email: urgentspellcast@gmail.com or Call or WhatsApp: +14243308109.

Read more about him on his website: http://urgentspellcast.website2.me/