A wheat stem sawfly look-a-like and white grub biocontrol

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A wasp commonly found during the summer in Kansas has recently caught the attention of some producers. In one instance, several wasps were mistaken for wheat stem sawfly (Cephus cinctus), a significant pest of wheat that has not yet established in Kansas. Large gatherings of this wasp in a corn field also raised concerns.

Sometimes referred to as flower wasps, the five-banded tiphiid wasp (Myzinum quinquecinctum), is a harmless solitary wasp found throughout most of the country. In Kansas, it is found statewide and is most common mid to late summer. These ¾ to 1 inch long, narrow bodied wasps have dark bodies, long antennae and smoky wings (Figure 1). Yellow markings are visible on their thorax and yellow bands are present on each abdominal segment. Subtle differences set apart males and females. Male wasps have yellow legs, while females have stockier orange-red legs and wider yellow bands on their abdominal segments.

Figure 1. Male flower wasp. Photo by Anthony Zukoff, K-State Research and Extension.

While similar looking, wheat stem sawflies are present earlier in the season, have fewer yellow bands on their abdomen and an all-black thorax (Figure 2). Wheat stem sawfly is also restricted to wheat fields, while flower wasps can be found anywhere.

Figure 2. Wheat stem sawfly. Photo credit: Pat Beauzay, NDSU.

Both male and female flower wasps visit flowers to feed on nectar. Females are parasitoids of various scarab beetle larvae, including a below ground pest common to many fields, white grubs. These wasps have been promoted as biocontrol tools in farm and turf settings and their presence is a good indicator that natural pest control is taking place. Female wasps seek out beetle larvae in the ground, digging for them with their stocky legs. She then deposits an egg on the body of the grub and injects a neurotoxin to paralyze it. As the wasp larva develops, it will consume the beetle larva. The wasp then overwinters as a pupa below the ground and emerges as an adult the following summer. Since the populations of both the wasp and its host fluctuate yearly, the level of parasitism changes from season to season. This results in some years where many wasps successfully overwinter and emerge in large numbers.

The female wasps are not commonly encountered. In fact, it is the male of this species that is most often noticed. This is due to the fact that the males tend to congregate together in large numbers on vegetation. The shade of corn fields (Figure 3) and, occasionally, large amounts of honeydew from aphid infestations in sorghum often attracts groups of these wasps. When approached or disturbed, the group of male wasps take flight and fly circles around the location, giving the appearance of an angry swarm of wasps. The males have no stinger and are harmless, however, the hooked appendage at the end of their abdomen is often mistaken for one, adding to the alarm. Despite their behavior and large numbers, these wasps are no threat to people or crops. As summer progresses, these groups of male flower wasps will slowly die off and eventually disappear.

Figure 3. Male flower wasps congregating on corn plants. Photo by Anthony Zukoff, K-State Research and Extension.



Anthony Zukoff, Extension Associate – Entomology, Southwest Research and Extension Center

Tags:  insects wasp