It can only be speculated exactly what occurred in the cell where the mantispine larva developed into an adult. What is clear is that the larva did not have access to its established preferred food source, spider eggs, but had access to the wasp larva, the immobilised spiders and its kin. While maintenance feeding of mantispine larvae on the haemolymph of spiders has been reported, development to the adult is not realised (Redborg and Macleod 1983). It is also worth noting that larvae tend to board spiderlings that emerge before the mantispine can commence with feeding rather than attacking the spiderlings (Redborg 1985). Cannibalism is unlikely as several reports of gregarious behaviour and multiple larvae boarding a single spider and sharing the host without malicious behaviour (Snyman et al. 2021). The mantispine could also perhaps have fed on the wasp larva. The wasp larva was recovered dead, perhaps lending the possibility of the mantispine feeding and killing the larvae through predation or perhaps producing an allomone that negatively affected the ontogeny of the wasp resulting in its death. Finally, spiders collected by wasps are often female (pers. comm. M. Ohl 2021). Since the wasp larva partially fed on the spider provisions, it is possible that a pregnant female spider could have been left partially eaten with eggs exposed and available to the mantispine larva.
The presence of the Mantispinae eggs on the nest also lends interesting interpretations. At first thought, it supports non-random ovipositing behaviour by the adult females. It can easily be argued that the female mantispine somehow realised the presence of suitable hosts, i.e., spiders. By ovipositing close to a potential “food source” will likely increase the chances of her minute offspring locating it. On the other hand, if females keep mistakenly ovipositing near wasp nests due to the presence of spiders but not spider eggs, the larvae will be at a disadvantage. Such a mechanism will likely not be favoured and will not evolve.
The events reported on here can probably be dismissed as an anomaly or mistake. Curiously, however, the mistake involved a nest-building hymenopteran. Such hymenopterans not only serve as mimicry models for other Mantispinae species, but also serve as a source of food for the larvae of a closely related taxon, the Symphrasinae.
Snyman et al. (2021) favoured a single origin of aculeate hymenopteran mimicry in Mantispoidea. The authors argued that the specialist diet of spider eggs probably originated by ‘proto’ mantispine larvae boarding wasps to gain access to its food source, hymenopteran pupae. Since spiders, a substantial source of food of various wasp species, would often be encountered in wasp nests, boarding spiders might also increase the chances of the ‘proto’ mantispine larvae to gain access to hymenopteran pupae, its food source. By boarding spiders, a plausible switch to spider eggs can thusly be postulated. A more random scenario of changing diet from pupa to spider eggs, generally protected by a protective silken sac, is however, not as easily explained (Snyman et al. 2021).
While the single origin idea proposed by Snyman et al. (2021) is appealing, this is seemingly not the case and mimicry probably evolved twice, once in Symphrasinae and once in Mantispinae. The mimicry in Symphrasinae possibly evolved, at least in part, to gain access to food as well as benefiting from being a Batesian mimic. In Mantispinae, however, the characteristic is probably a derived one and evolved in a Batesian system only, where the mimics frequents flowers as hunting platforms, the same flowers utilised by the model wasps for maintenance feeding (Pascarella et al. 2001). Even though mimicry seems to be quite plastic, once present in a species, it is not easily lost (Prudic and Oliver 2008). In times of an allopatric existence between the mimic and model the mimesis might wane without going extinct, and return once the model and mimic occurs in sympatry again (Prudic and Oliver 2008). So perhaps a “mimicry predisposition” can at least serve as a tenuous connection between aculeate Hymenoptera and both Symphrasinae and Mantispinae. Reverting to a far-removed ancestral food source, after the establishment of a specialised diet, proves more difficult to explain and is thought to be governed by both ecological and phylogenetic determinants (Pekár et al. 2011). This will also assume that the ancestral diet of the raptorial Mantispoidea was aculeate hymenopteran brood. Reverting to an ancestral food source occurs due to an apparent residual capacity to use ancestral hosts, at least in phytophagous insects (Ikonen et al. 2003; Gassmann et al. 2006). This pattern might even be more common than to establish a new host association due to novel barriers that may be involved in moving to a new host (Gassmann et al. 2006). This might then imply that the host preference of Rhachiberothinae, Drepanicinae and Calomantispinae should likely also be brood of Hymenoptera. Rare reports such as this, should however, be interpreted with caution as it might lend itself to be “over-interpretated”. Nevertheless, the association described here certainly warrants closer inspection and elucidating variation in mantispinae larval diet should perhaps be revisited using choice and no-choice experiments.
In conclusion, the occurrence of Afromantispa now includes the Oriental region. The evolution of the Mantispoidea is complex and despite being on the receiving end of multiple recent studies, still not well understood. Perhaps a better understanding of the dietary range of Rhachiberothinae, Drepanicinae and Calomantispinae will elucidate the curious connection between taxa within Mantispoidea and the aculeate Hymenoptera.