The Bean Bosses

Kelly’s Field Notes

Common Name: Chocolate midge

Order: Diptera

Family: Ceratopogonidae

Genus: Forcipomyia (alternative genus spelling Euprojoannisia)

Species:

• Forcipomyia squamipennis

• Forcipomyia hardyi - native to Hawaii and pollinate cacao (Theobroma cacao) grown there

Description:

There are about 1,000 species of midges within this genus. They are teeny tiny, the size of a pinhead (1-3 mm in length). Their small size allows them to get into the equally small spaces of the cacao flower. Midges from this genus are brown-grey or black and white in color.

Pollinating Cacao:

Like our friends the mosquitoes, biting midges feed on nectar and the females feed on blood in order to obtain enough protein to create eggs. Because most of the time they are not creating eggs, the majority of their food is nectar. Thankfully, this tiny biting midge is small enough to pollinate one of mankind’s favorite plants, cacao. Although they are so small they can only carry enough pollen to pollinate one flower. While other species have been noted visiting cacao flowers they are either considered pollen thieves (bees) that do not pollinate in return, or we do not have enough information to know for sure if they are thieving or pollinating. We do know, however, that gall midges (Cecidomyiidae) also pollinate cocoa but to a much lesser degree. Additionally, one study in Bolivia suggests midges are only responsible for 2% of cacao pollination there, so there may be other important pollinators we are not aware of.

The Hawaiian island of Oahu and the National Park of American Samoa have species of the chocolate midge pollinating chocolate plants there. The natural habitat of chocolate midges and cacao is shady and humid, but cultivated cacao is grown in open, sunny areas. Invertebrates rely on humidity to save them from desiccation, so a dry sunny spot is not good habitat for a tiny midge. Because of this, cultivated cacao pollination percentages are very low, with only 3 blooms in 1,000 getting pollinated. There is also the issue of the short lived cacao flower, which dies and falls off of the tree in 36 hours if not pollinated. Hand pollination is far more successful than relying on midges to get there in time enmasse.

Life Cycle:

The life of a midge begins right after a mating swarm happens and a female is inseminated. She then finds a host, whether that be vertebrate or invertebrate (sub Genus Lasiohelea) and bites them for their blood or hemolymph. When she has enough protein to form eggs, she lays about 90 of them within damp plant detritus or in animal droppings. Midges go through complete metamorphosis; egg, larva, pupa, adult. The egg stage lasts about 2 to 7 days.

Biting midge larvae are tiny, only 2 or so mm in length. According to laboratory studies, they are gregarious and prefer to stick together. They also attempt to defend themselves when distrubed with “vigorous movements” which is thrashing about. The larvae feed on the detritus until it is time to pupate. This stage can last from 2 weeks to 1 year, depending on the species and environmental conditions. The pupal stage is nice and short, only lasting 2 to 3 days.

Once they eclose (emerge) as adults, midges tend to stay pretty close to home. Most do not move beyond 6m of their resting places. They hang out in the shaded areas and come out to bite, forage, and mate at dusk and dawn. Their lives as adults last between 2 and 7 weeks.

Super Powers:

• Tiny - midges in general are so small they are very difficult to squash! Think Antman and his shrinking suit.

• Too Important to Jail - though biting midges are incredibly annoying, I think most of us would forgive them because they give us chocolate. They are almost a super villain in that capacity! Many people are sensitive to these bites and experience swelling and itchiness.

• Desire - chocolate is sexy and considered an aphrodisiac in many cultures. Thanks to the midge!

• Excellent Sense of Smell - like many “bugs” our frienemies the midges are great at detecting odors so they can find flowers to feed from.

Chocolate midges in Culture:

• Thanks to midges, the cacao plant, which originated in the Western Amazon region of South America, has been cultivated for more than 3,000 years in Central and South America.

• As of 2017, the cacao industry is an $80 billion year industry with 3.5 million tonnes produced annually.

• Queen Victoria mentions in her diary how bad biting midges were when she was trying to picnic in Sutherland. Even royalty are not exempt from their annoying bites!

• Biting midges may also be responsible for whiskey! The Picts, and ancient people of Scotland, produced heather ale as long ago as B.C. 325, using heather pollinated by biting midges. The myth about whiskey is that the steam from the heather ale condensed within a stone roof cottage and dripped off into a cup, creating the first whisky.

Book Recommendations:

McAlister, Erica. The secret life of flies. London: Natural History Museum, 2017.

References:

Biting Midges. Purdue University. extension.entm.purdue.edu/publichealth/insects/bitingmidge.html.

Chumacero de Schawe, Claudia, et al. "Abundance and diversity of flower visitors on wild and cultivated cacao (Theobroma cacao L.) in Bolivia." Agroforestry systems 92.1 (2018): 117-125.

Cornejo, Omar E., et al. "Population genomic analyses of the chocolate tree, Theobroma cacao L., provide insights into its domestication process." Communications biology 1.1 (2018): 1-12.

Kaufmann, Tohko. "Behavioral biology of a cocoa pollinator, Forcipomyia inornatipennis (Diptera: Ceratopogonidae) in Ghana." Journal of the Kansas entomological society (1974): 541-548.

National Park of American Samoa. U.S. National Park Service. www.nps.gov/npsa/index.htm.

Pollinators - Chocolate Midge. U.S. National Park Service. www.nps.gov/articles/chocolate-midge.htm.

Toledo-Hernández, Manuel, Thomas C. Wanger, and Teja Tscharntke. "Neglected pollinators: Can enhanced pollination services improve cocoa yields? A review." Agriculture, ecosystems & environment 247 (2017): 137-148.

Young, Lauren. “The Unexpected Pollinator of the Cocoa Tree.” Science Friday, 29 Dec. 2017, www.sciencefriday.com/articles/meet-the-flies-that-pollinate-cocoa-trees.