Used to flavour stews or eaten on their own, stinkbugs are said to have a crunch to them and taste a little like apple. Prepared by boiling, the bugs release defensive pheromones in a last ditch attempt to survive, and while it hurts the eyes it’s no more successful than the onion’s weak survival attempt.
Insects account for more than 80% of all living animals on earth and have existed for over 500 million years. Their consumption by humans dates back to pre-biblical times (Leviticus 11: 21–23). There are over 1 900 species of insects that are known to be edible by people of different cultures around the world, with 102 belonging to the order Hemiptera (bugs). Amongst the 102 is the relatively large, shield-shaped edible stinkbug (Encosternum delegorguei) native to southern and central Africa. This species is a sought after delicacy in rural villagers in Malawi, South Africa and Zimbabwe. It is considered highly nutritious with proteins made up of essential amino acids (Teffo 2007).
How to recognise an edible stinkbug
Edible stinkbugs are light green-yellow, shield-shaped bugs with dorsally flattened bodies averaging 25 mm in length. Their heads are small and triangular with two brown shiny compound eyes and a pair of five segmented antennae. They possess forewings that are hardened at the base and membranous at the tips; the hardened bases are separated by a triangular scutellum. Nymphs are red and wingless.
Getting around
They are strong fliers and will congregate in specific areas during the dry season. Villagers talk about swarms migrating to hilly areas and valleys. During the night and cold weather, they remain immobile in large clumps where they are vulnerable to being harvested.
Distribution
Distribution of this species ranges from southern Africa northwards to the Democratic Republic of Congo. In southern Africa it is widely distributed within the tropical/subtropical woodlands and bushveld of South Africa, Botswana, Swaziland, Malawi, Mozambique and Namibia. South African populations have been recorded in the vicinity of Thohoyandou, Ga-Modjadji and Bushbuckridge.
Habitat
During the dry season they congregate at higher altitudes than the wet season distribution and aggregate in sunny tree top locations in tropical bushveld and open woodlands. The wet season distribution is more widespread and linked to the availability of food plants (Dzerefos et al. 2015).
Food
They are plant eaters that feed on Combretum imberbe, Combretum molle, Peltophorum africanum and Dodonaea viscosa.
S£X and LIFE CYCLES
Reproduction is s£xual. Mating occurs between mid-October and late November (spring) (Dzerefos et al. 2009). Hard-shelled eggs are laid and glued on the grass stems and twigs of food plants ten days after copulation and hatching occurs 18 days thereafter. Hatchlings are small and wingless nymphs that resemble adults except for the colour. Nymphs undergo four successive stages known as instars where they moult; changing colour and becoming more adult-like with wings.
THE BIG PICTURE
Friends and foes
The most important enemies of the edible stinkbug are humans who extensively harvest them for food. They are also preyed on by monkeys, birds and ants. Recently parasitoid wasps that prevent hatching of eggs have been documented (Dzerefos et al. 2009); the wasps lay their eggs in the eggs of the stinkbugs, and the wasp larvae feed on the embryo of the stinkbug eggs. Other than predators, they are faced with habitat degradation influenced by land use and felling of food trees.
Smart strategies
Most food plants of the edible stinkbugs lose their leaves during the winter season. Consequently, these bugs are faced with reduced food sources. To combat these challenges, they secrete wax during winter to insulate their body, and undergo diapause during which they avoid feeding and only take in droplets of water. To fight against predators, the species employ a chemical defence mechanism.
It secretes chemicals that stain hands yellow or orange and has an unpleasant smell. The chemicals are also known to cause temporary blindness if they come into contact with the eyes. To increase their defences against predators, they aggregate in tree tops to combine their defence chemicals. The aggregation behaviour also helps in maintaining body temperature during winter and enhances mating opportunities during mating season.
Poorer world without me
Consumption of edible insects has been a major driver for plant conservation, with many plants conserved simply for the reason that they host a particular edible insect of significant value to consumers. Edible stinkbugs have been used to promote conservation of the Jiri forest of Zimbabwe. As a result of the human–forest–stinkbug relationship, the use of more than 10 indigenous plants species within this forest has been forbidden and deforestation has been avoided.
Most of the forbidden plants are those that these stinkbugs aggregate on. During the harvesting season of stinkbugs, a team of caretakers who ensure that ethical and sustainable harvesting is practiced in the Jiri Forest is employed by the Norumedzo villagers who are highly dependent on the forest. The awareness of cultural, social and religious significance of this species has played a great role in the conservation of this forest (Munyaradzi 2014).
Edible stinkbugs have been served as food in South Africa, Malawi and Zimbabwe for generations. In South Africa, they are a delicacy for the Venda people of Limpopo and for the Mapulana people of Mpumalanga. They are an important source of protein, vitamins and micro-elements. Their palatability depends on the successful removal of the bitter tasting and stinking defence chemicals. After they are harvested, the live stinkbugs are separated from the dead ones.
The heads of the dead ones are removed and the defence chemicals are squeezed out through the opening. The live ones are put in warm water and stirred. In distress, they secrete all their defence chemicals into the water and the water is discarded (this is repeated at least once). They are then boiled for several minutes before they are sun-dried. The dried ones can be fried with a little salt. Some people eat them dry as a snack. They also have increasing economic value for harvesters who sell them. I
n 2009 a cup of dried edible stinkbugs cost an average of R5.00, and then R10 in 2013 and this year (2015) a cup fetches an estimated R20.00 in Thohoyandou. Edible stinkbugs are also used to aid with digestion, act as appetizer and as a cure for hangovers.
Conservation status and what the future holds
This species has not been assessed according to the IUCN red list criteria and so its conservation status is unknown. In a global context, edible stinkbugs are widely distributed from southern Africa northwards to the Democratic Republic of Congo, but have only been documented as food in Malawi, Zimbabwe and South Africa. However, populations in South Africa not only face threats of habitat degradation, spread of invasive alien organisms, environmental pollution and pesticides, but could also succumb to over exploitation resulting from its increasing economic value.
Tessaratomidae is a family of true bugs consisting of about 56 genera recorded. The family is also referred to as giant shield bugs because of their relatively large bodies. They share a similar arrangement of piercing or sucking mouthparts known as the rostrum. E. delegorguei bear a striking resemblance in morphology to members of the family Pentatomidae such as Chinavia spp. and Nezara spp. They differ in that members of Pentatomidae have an enlarged triangular scutellum, which is extended to partially cover the wings.
Edible insects could contribute to the world’s food security, says Baldwyn Torto, a scientist at the Kenya-based International Centre for Insect Physiology and Ecology (icipe) and a corresponding author of the study.
Torto adds that most communities do not know which edible insects are truly nutritional and have beneficial effects on human health.
“This is what inspired our research to contribute to food security and income generation among the communities … across the African continent. Some of the traditional foods including insects consumed such as the edible stink bug are highly nutritious and beneficial to human health and should be promoted into mainstream diets,” Torto tells SciDev.Net.
The study, published in the PloS ONE journal on 5 January, resulted from funding from the German Academic Exchange Service to aid postdoctoral fellowships in African centres of excellence.
“Our policy recommendation is that carbohydrate-based diets such as cereals and cassava can be fortified with powdered, processed edible stink bugs to improve their nutritional uptake,” explained Torto. “We further recommend the creation of a database of all insects consumed across Africa to allow scientists to investigate their nutritional and health benefits and to develop methods for their mass rearing, processing and use to improve nutrition in deficient communities.”
Researchers from Kenya and Zimbabwe collected stink bugs — known scientifically as Encosternumdelegorguei — from Jiri Forest in south-eastern Zimbabwe during June 2014 as the period May to August coincides with the insect’s highest abdominal fat composition.
The researchers created four harvesting quadrants that covered the entire forest. In each quadrant, they harvested the stink bug from branches of ten randomly selected trees. The researchers searched for chemical components such as antioxidants, amino acids, essential fatty acids and toxins.
“We found high protein, fatty acids and anti-inflammatory chemicals such as flavonoids content,” says Torto, adding that the edible stink bug has the potential to help lessen nutrient-deficient communities in Africa where vegetables and animal sources may be limited.
The researchers identified seven essential fatty acids for human nutrition and health out of the ten they found, four flavonoids and 12 amino acids, including two considered to be the most limiting in cereal-based diets.
But Torto warns that like other food sources such as cereals and vegetables, harvesting and processing of the stink bugs require use of appropriate storage procedures to avoid contamination with poisonous moulds which produce chemicals such as aflatoxins known to negatively affect human health.
