Wednesday, July 20, 2016

June Beetle Time!

It happened. As I was walking back from lunch my friend and I saw them, buzzing around like little fighter jets. These insects were not wasps, or flies, or dragonflies, but green June beetles (Cotinis nitida (L.)). You'll probably see them too, soon. Then in a few weeks they'll be gone. Well, at least the adults will be.

An adult green June beetle (Cotinis nitida)

Several scarab beetles are called "June beetles" or "Junebugs". Some are more properly referred to as May beetles* such as the brown or reddish-brown Phyllophaga and some Serica species (both in the subfamily Melolonthinae). Other beetles typically called June beetles include the lined June beetles in the genus Polyphylla which are also members of the Melolonthinae.

Green June beetles, however, are members of the beautiful and diverse subfamily Cetoniinae, or flower chafers. This group is typically distinguished by a flat appearance, antennal attachments that can be seen from above, and, in some groups, distinct "shoulders" (humeri - seen as little triangles in the front corner of each wing cover in the photo above). Many members of the group are vividly colored and some are enormous - in fact among the largest insects in the world are the aptly named Goliath beetles (Goliathus spp.).

The species itself is a beautiful emerald green with hues of bronze and tan. Some areas of the body are shiny while others are more flat. It's head looks like it's been hammered out of metal, complete with a horn and a ridge:

Close up of a green June beetle head

These beetles measure about an inch long and, thus, are quite noticeable. There are several species in the genus Cotinis, but the only one in North Carolina is C. nitida. Another local relative, Euphoria fulgida, is similarly colored, but has a triangular scutellum in between the wing covers.

Green June beetles are among the fastest flying beetles around**. It takes a second to determine that they are in fact a beetle and not some large bee or wasp - this can create some momentary terror for those afraid of stinging insects when they are buzzing around. Their rapid flight is aided by the fact that, unlike most other beetles, their wing covers (elytra) remain closed during flight. In fact they are fused and the wings slide out the sides when in use. This makes them particularly streamlined and agile, rather than exhibiting the clumsy flight of other beetles. Although they may come to lights, these beetles are most active during the day.

The western species Cotinis mutabilis in flight. Note how the wing covers are closed during flight, unlike most other beetles. Photo by Dennis Ancinec

So where are they going so quickly? Well, adults (like most adult animals) are interested in two things: mating and eating.

Upon emerging from the ground (more on the life cycle below) the beetles are eager to mate. Females generally stay on the ground and produce a pheromone which attracts numerous suitors. After mating multiple times, the takes off along the ground to find a suitable spot to lay her eggs.

On the food side, green June beetles are known to be pests of soft-skinned fruits and vegetables. This is where their other names come from: fig-eaters or fig beetles. Although not exclusive to figs, these beetles will also attack peaches and other stone fruits, pears, apples, grapes, bramble fruits, tomatoes and corn, among others. They typically attack ripe or over-ripe fruits that are easier to break open and produce early fermentation chemicals we can't detect with our nose. Once at the fruit, the beetles emit a chemical that brings others to the food source, causing a snowball effect which can spill over to other fruits. The physical damage along with fecal matter from the beetles fouls the fruit making it inedible. The feeding, however, increases the reproductive potential of the beetles.

A group of green June beetles attacking a ripe pear. The fruit will be ruined for consumption. Photo by J. Reynolds

Females look for soil that has a high organic matter content, preferring areas with decaying vegetable matter and dung on which the larvae feed. Digging into the ground with their strong, rake-like forelegs and horn, the female lays from 10-30 eggs in a ball of soil and organic matter. She will continue to feed, mate and lay eggs several times.

Larvae go through three instars in the ground. In addition to feeding on organic matter, larvae sometimes cause damage to plants by eating roots. Their digging may also disrupt the root system, especially on turfgrass. Thus both adults and larvae are economically important (though only in some situations). Larvae often live in pastures and fields, but have also been found in leafcutter ant mounds in TX. They can be seen crawling on their back after rains flush them out of the ground; they also travel this way in the soil. This back-crawling behavior is unique and an easy way to quickly identify larvae.

This larva is just the way it likes to be: larval green June beetles are typical white grubs, but atypical in that they travel on their back when moving on the ground or quickly through the soil.

Green June beetles go through one generation per year. The larvae that hatch in the summer from eggs feed until the cooler months when they await the next year's warming spring season. They resume activity for a short time and then spend a few weeks as a pupa, before emerging again in the summer as an adult.

As far as pest status and control, green June beetles are most often an issue in and around pastures. Damage by larvae is characterized by patches of loose turf caused by destruction of roots. As described above, the adults often attack various fruits, but fields and orchards around grassy areas that apply manure or have livestock may be at highest risk for attack by adult beetles. Several types of chemicals are available to apply for control of larvae, and should be treated soon after the larvae hatch in late summer, after breeding season. As far as adults, monitoring using fruit baits near the edges of fields containing fruit crops can help identify the timing and density of the beetles. However, note that like Japanese beetle traps, these bait stations may actually draw beetles nearer to fields. Knowing the local history of outbreaks can also aid in predicting risk.

Colored SEM of a green June beetle by Daniel Kariko 
* these names are generally based on the timing of usual emergence, despite changes in climate likely affecting this window
** you get interesting results when searching for Cotinis + flight