Images: Rob C. H. M. Oudejane
Common names: Cockroach-hunting wasp, cockroach wasp (Eng.); kakkerlakwespe (Afr.).
Ampulex is a genus of aculeate (meaning animal that possesses a sting) parasitic wasps known as cockroach-hunting wasps. A better-known species in the genus is the emerald cockroach wasp (Ampulex compressa) found in other parts of Africa, Asia and the Pacific Islands, but which has not been recorded in South Africa. However, South Africa hosts a total of 35 of the 132 species described to date (Pulawski 2023).
The life history straits of Ampulex bantuae have been studied by Gess (1981). This species leads a secretive life, and it is rare to find in its natural environment. They live in trap nests suspended from the horizontal branches of the sweet thorn (Vachellia karroo) at heights of 10 cm to 2 m above ground in subtropical forests and woodlands. They utilise the disused galleries of a beetle species (Ceroplesis hottentotta: Cerambycidae) as nesting sites. The nesting cavities are provisioned with cockroaches for completing the lifecycle (Gess 1981).
Description/How to recognise a…
Ampulex bantuae is a parasitic medium-sized wasp that is metallic blue in colour. The females of the species can reach up to 14.5 mm in size, while males are known to reach 12.0 mm. The adult males of the species are fully winged while the females are apterous (wingless).
The male and female nymphs are similar in appearance but may be readily distinguished in all instars by differences in the form of the terminal abdominal sternites. Little information on the life history traits of the male of the species is available. The females provision their nesting cavities with a cockroach, Bantua dispar, a blattid.
Getting around
The wasps hunt the cockroach on foot by moving quickly but by fits and starts, while twitching the wing-like structures, which are held folded over the back. Their antennae are held out in front of the head and used as feelers. These antennae are curved out to the sides and are kept in constant motion, drumming the surface on which the wasp is walking. Each antenna as a whole describe an elliptical path, the direction of the movement of one is clockwise while the other one is anticlockwise. Together they are brought down towards the surface, move inwards towards each other, are raised up and move apart. At the same time the abdomen is moved up and down continually and is also frequently moved in and out telescopically (Gess 1981).
Communication
There isn’t much known about the courtship and mating behaviour of cockroach-hunting wasps. However, parasitic wasps in general use acoustic and vibratory signals for sexual communication, mate recognition, courtship and mating processes. In parasitic wasps, courtship consists of a series of highly specific reciprocal stimulus-response sequences between the sexes (Matthews 1975; Danci et al. 2014).
Distribution
Ampulex bantuae is currently known to occur only in South Africa. This includes parts of Mpumalanga and the Eastern Cape (Pulawski 2021).
Habitat
Ampulex species are found in subtropical forest and woodland. Usually on tree trunks (Picker et al. 2019).
Food
Once the female wasp locate a suitable cockroach, it advances upon the cockroach with widely separated mandibles and positions itself favourably forward and seizes the cockroach by the anterior part of the pronotal shield (head shield), with one mandible positioned on the upper surface and the one on the lower surface of the shield.
The wasp then moves her abdomen downwards and forwards between its widespread legs to bring the tip of the abdomen into position on the underside of the prey and while still retaining its hold on the shield. In this position the wasp delivers a sting in the neck area of the cockroach. The stung cockroach stops struggling and lies still, its legs unable to support its weight (Gess 1981).
The sting contains venom that inactivates the central motor networks temporarily and causes temporary paralysis to the cockroach forelegs for 1–2 minutes and is followed by a more delicate sting into the host’s neck. The wasp then leaves the paralysed cockroach to search for a suitable nesting site and the stung cockroach does not leave the site but start to excessively groom itself (Libersat & Gal 2013).
Upon her return, once the cockroach stands from that near death experience, the wasp reaches with her head and mandibles below the pronotal shield covering the head of the cockroach and takes hold and draws forward one of the antennae. The wasp then pulls the cockroach like a dog on a leash towards the nesting cavity. While the wasp is pulling the antenna of the cockroach it also imbibes the haemolymph (insect blood) oozing form the cut ends (Libersat & Gal 2013, 2014).
On arrival at the nesting cavity, the wasp enters it backwards and continues backing in until she reaches the inner end, while still pulling the cockroach. Once satisfied, she lays one egg on the underside of the cockroach. Once oviposition is completed the wasp squeezes past the cockroach and emerges from the nest. She collects small decaying matter to seal the nest cavity (Gess 1981).
Sex and life cycles
Ampulex wasps are solitary wasps. In this group, the adults live for several months. Mating takes about a minute, and only one mating is necessary for a female wasp to successfully parasitise several dozen cockroaches The wasp lays one to two white eggs (about 2 mm long) between the roach’s mesothoracic (middle) legs.
With its escape reflex shut down, the cockroach becomes a lazy and compliant living ‘zombie’ host, fed on by the wasp’s offspring. Three days after oviposition, when the first instar larva emerges after hatching, it pierces the soft cockroach cuticle to feed on haemolymph for four to five days. The larva continues to feed through the second instar, after which it moves into the cockroach’s body and feeds on its internal organs.
This stage lasts for about eight days as the larva prepares for pupation. A multilayered, spindle-shaped silken cocoon, thick and chocolate-coloured, gets spun out by the larva. This pupation takes several weeks. Finally, a fully grown adult wasp emerges from the hollow body of the cockroach and completes the life cycle. Development is faster in the warm season (Bressan-Nascimento et al. 2006).
THE BIG PICTURE
Friends and foes
The cockroach-hunting wasps feed on cockroaches and are important food sources for birds and other insects like mantises.
Smart strategies
The female wasp attacks the cockroach and immobilises it through two separate venomous stings. The first sting is delivered to the mass of nerve tissue in the cockroach, paralysing its front legs for a few minutes. The combination of chemical compounds injected through the venom prevents the cockroach from defending itself and stops any movement. The wasp takes this opportunity to inject its second sting.
The second sting administered by the wasp is very precise and aimed at the head area of the cockroach. The neurological transmitter called octopamine, which controls muscle contraction in sudden movements in the cockroach’s body, gets limited after the second sting. The wasp gains thus gains the upper hand and start pulling the cockroach to the selected nest cavity to lay eggs on it, thereby starting the cycle.
Poorer world without me
Aculeate wasps play significant roles in the ecosystem as predators of other insects. For example, several Ampulex species are used successfully as biological control agents for domestic cockroaches. They are also known as pollinators of more 1 000 plant species across a range of different habitats. They indirectly support the ecosystem functioning through seed dispersal and decomposition (Brock et al. 2021).
People and I
Wasps do not have a good relationship with people because of our perceptions of these creatures. This dislike is largely shaped by a subset of species representing 1% of the aculeate wasps. Although wasps feature in some artwork and culture mainly in the Asian countries, the negativity associated with these creatures outweighs any of these positive outlooks. Aristotle called them creatures that lack extraordinary features and are devoid of divine characters like bees (Brock et al. 2021).
In an online survey conducted by researchers in the United Kingdom and Italy with 750 participants, the word ‘sting’ was used devastatingly to describe wasps, but not bees (although they also sting). In the same study the participants believed that there was nothing useful or beneficial related to wasps, but bees were described as important for pollination (Sumner et al. 2018).
In films, wasps are depicted as the mistreated female star of the thriller, The Wasp Woman, where she becomes an evil, man-devouring ‘wasp’ by night (Corman 1959); while in another film, Dragon Wasps, the over-sized, fire-breathing wasps are the antagonists. It is time that researchers and society in general shift their negative perception of wasps and learn to appreciate their positive role in the ecosystem.
Conservation status and what the future holds
The conservations status of Ampulex species has not yet been evaluated. However, the many and important ecosystem services provided by stinging wasps in general may provide the necessary impetus for humans to shift their perceptions of wasps to a more positive and tolerant one. In countries like South Africa where the insect pollinators are in decline and affecting food production, this shift is a necessity (Melin et al. 2014).
We will need effective marketing strategies of the benefits of wasps as valuable, natural commodities that contributes to our health and food security (Hart & Sumner 2020). These may help raise awareness around wasps and change the perceptions of people to ensure they are more valued in conservation, alongside other beneficial insects like bees.
RELATIVES
There are about 134 species of Ampulex described globally of which 35 occur in South Africa (Pulawski 2023).
Official Common Name: Cockroach-hunting wasps
Scientific Name and Classification:
Kingdom: Animalia
Class: Insecta
Order: Hymenoptera
Family: Ampulicidae
Genus: Ampulex
Species name: A. bantuae Gess, 1984
Derivation of scientific name: The name is derived from a South African cockroach genus Bantua, of which one species Bantua dispar is the only known prey for this cockroach-hunting wasp species.
References and further reading
- Bressan-Nascimento, S. 2006. On the morphology of the juvenile stages of Ampulex compressa (Fabricius 1781) (Hymenoptera, Ampulicidae). Zootaxa 1279: 43–51.
- Brock, R.E., Cini, A. & Sumner, S. 2021. Ecosystem services provided by aculeate wasps. Biological Reviews, 96(4): 1645–1675.
- Corman, R. 1959. The Wasp Woman. Allied Artists Pictures Corporation, Glendale.
- Danci, A., Inducil, C., Takács, S., Schaefer, P.W. & Gries, G. 2014. Mechanism of mate detection in parasitoid wasps: sound and vibratory cues change with the developmental progress of future mates inside host pupal cases. Physiological Entomology, 39(4): 292–303. doi:10.1111/phen.1207
- Gess, F.W. 1981. Some aspects of an ethological study of the aculeate wasps and the bees of a karroid area in the vicinity of Grahamstown, South Africa. Doctoral dissertation, Rhodes University.
- Gess, F.W., 1984. Contribution to the taxonomy of the southern African species of Ampulex Jurine (Hymenoptera: Sphecidae: Ampulicinae). Annals of the Cape Provincial Museums. Natural history 16(1):1–22.
- Hart, A.G. & Sumner, S. 2020. Marketing insects: can exploiting a commercial framework help promote undervalued insect species? Insect Conservation and Diversity 13: 214–218.
- Libersat, F. & Gal, R. 2013. What can parasitoid wasps teach us about decision-making in insects? Journal of Experimental Biology 216(1): 47–55.
- Libersat, F. & Gal, R. 2014. Wasp voodoo rituals, venom-cocktails, and the zombification of cockroach hosts. American Zoologist 54(2):129–142.
- Matthews, R.W. (1975). Courtship in parasitic wasps. In: Price, P.W. (eds) Evolutionary strategies of parasitic insects and mites. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-8732-3_4
- Melin, A., Rouget, M., Midgley, J.J. & Donaldson, J.S. 2014. Pollination ecosystem services in South African agricultural systems. South African Journal of Science 110(11–12): 1–9.
- Picker, M., Griffiths, C. & Weaving, A. 2019. Field guide to insects of South Africa. Penguin Random House South Africa.
- Pulawski, W.J. 2023. Catalog of Sphecidae sensu lato (= Apoidea excluding Apidae) Available at < https://www.calacademy.org/scientists/projects/catalog-of-sphecidae>. Last accessed October 2023.
- Sumner, S., Law, G. & Cini, A. 2018. Why we love bees and hate wasps. Ecological Entomology 43(6): 836–845.
Author:
Rethabile Motloung
E-mail: r.motloung@sanbi.org.za