Zonitis Bilineata on Sunflowers

Aug 06, 2021

By Adam Varenhorst

While scouting sunflower last week we noticed beetles that were present throughout the field on the developing buds. These beetles weren’t feeding on the buds or the bracts that they were often on. So, what were they doing on the sunflowers? We determined that these stationary beetles were a species of blister beetle, but unlike some of their relatives, they weren’t feeding on the green leaf tissue. We know that many blister beetles are attracted to flowering plants, but the field wasn’t flowering yet. We determined the beetles were Zonitis bilineata. This particular blister beetle doesn’t have a common name although a few researchers have described it as the two-lined blister beetle or two-lined Zonitis, which is derived from bilineata (bi = two and lineata = lined).

Description and Behavior

Figure 1. Zonitis bilineata adult with distinct black lines on abdomen. Photo courtesy of Philip Rozeboom.

Zonitis bilineata are ¼ to ½ of an inch in length. They have an orange head, thorax and legs. Their abdomen is covered by cream-colored hardened forewings that have a black line on each side (Figure 1). However, we’ve observed that these lines can vary among beetles with some being very large and obviously black to some being faded thin lines (Figure 2).

Zonitis bilineata adult with faint lines on abdomen

Figure 2. Zonitis bilineata adult with faint lines on abdomen. Photo courtesy of Philip Rozeboom.

The adults lay eggs on the underside of sunflower leaves. When the eggs hatch, the larvae will eventually move to the face of the flower. They will rest on the sunflower face until a bee approaches and then they will latch onto the bee using their mouthparts. The larvae use this strategy to then get carried to the bees’ egg chambers where they will be sealed in. The larvae of Zonitis bilineata first eat the egg that the bee laid in the cell, and then they will use the pollen and honey provisions for food.

Management

There are no management recommendations for these insects. Although we can’t find any information regarding the cantharidin concentration present in these beetles we recommend that you avoid handling them as they may still cause blistering.

Source : sdstate.edu

Video: Turning Plant Defense Into a Management Strategy

Turning Plant Defense Into a Management Strategy

Understanding how a plant responds to stress is one thing.

Using that knowledge to make better management decisions is another.

Systemic acquired resistance, or SAR, is the plant's more direct defense response. When stress or infection occurs, the plant begins signaling throughout its system and preparing defensive compounds.

But if we know that response exists, can we help prepare the plant before the stress arrives?

The answer starts with understanding what triggers the response and what the plant needs to carry it out.

The Trigger and the Fuel

Salicylic acid plays an important role in triggering the SAR pathway.

Think of it as turning the truck on.

The engine may be running, but it still needs fuel to do the work.

In this case, manganese plays an important role in supporting the enzyme systems involved in the plant's defensive response.

This makes manganese status an important part of the conversation. Whether a producer is using tissue testing, sap analysis, or simply scouting for visible deficiency symptoms, the goal is to make sure the plant has adequate manganese available.

Manganese is required in relatively small amounts, but that does not make its role small.

If the plant receives a signal to defend itself but lacks the nutrition needed to support that response, it may struggle to carry out the process efficiently.

The trigger matters.

The fuel matters too.

Prepare Before the Stress Arrives

The best time to think about stress management is before the plant is overwhelmed.

Once a crop is already struggling, management can quickly turn into a game of catch-up.

This is similar to nitrogen management. Once a plant becomes severely deficient, correcting the problem does not necessarily erase the time and yield potential already lost.

Plant defense can work the same way.

Low-rate, targeted approaches designed to support the SAR pathway may fit best ahead of an expected stress event rather than after significant damage has already occurred.

That requires producers to think about predictable stress.

We may not know exactly what the weather will do tomorrow, but we generally know summer heat is coming. We know certain field conditions increase disease pressure. We know a herbicide application can temporarily stress a crop as the plant processes the chemistry.

Even a properly timed and labeled herbicide application can create a temporary response in the plant.

That does not mean the herbicide is bad.

Weeds can create significantly more yield loss than the temporary stress caused by controlling them.

The question is not whether we should eliminate every stressor.

The question is whether we can better prepare the plant to manage necessary and predictable stress.

Not All Stress Is Bad

Stress is a normal part of plant growth.

A perfectly stress-free environment does not exist in the field.

In fact, some stress is necessary for normal plant development. A plant responds to wind, temperature, moisture, sunlight, and countless other environmental signals throughout the season.

The environment is stress.

The plant's job is to manage it.

Problems begin when the stress load becomes greater than the plant's ability to respond.

Extreme heat, drought, high salt concentrations, disease pressure, and even certain management practices can add to that load.

This is where understanding SAR becomes useful.

Instead of waiting until the plant is visibly struggling, producers can begin identifying periods when stress is likely and make management decisions around those windows.

ISR Starts With the Soil

While SAR is a more direct defense response, induced systemic resistance, or ISR, brings the conversation back to soil health.

The longevity of a farm is closely connected to the health of its soil.

Carbon plays a major role because it supports biological life within the soil. Bacteria, fungi, and other organisms interact with plant roots and influence how the plant grows, accesses nutrients, and prepares for stress.

This is why soil health cannot be reduced to one product or one application.

It is a system.

Keeping living plants in the field longer can support biological activity. Cover crops may fit some operations. Better water management can improve soil conditions.