This week let’s have a look at a member of the Ant-like flower beetles, the Anthicidae, and particularly a species of the genus Notoxus in the subfamily Notoxinae. Notoxinae merit their subfamily status by virtue of the characteristic “horn”’ on the pronotum (the first segment of the thorax). As you can see from the image the horn projects forward, completely shielding the head. The projection probably protects the head from potential predatory attacks or, perhaps, from getting wet during heavy rainfall, but recent study has shown that for some Notoxus species the head can swivel up to engage the pronotum and that, together, they can be used as a shovel-like tool, pushing their way through sand and accumulated pieces of leaf litter.
Interestingly, many of the Notoxinae contain cantharidin, a poisonous compound also found in members of the beetle family Meloidae (Blister beetles). The latter were the notorious source of “Spanish fly”, an aphrodisiac popular in Europe during the 19th century, whose use was responsible for many deaths. Cantharidin is probably made de novo by the Meloidae. How the Notoxinae acquire their cantharidin is not known. The common name of the family (ant-like flower beetles) may be a clue since it suggests that its members are often found on plants (flowers) and many plants synthesize cantharidin and similar compounds. Notoxus may feed on those plant parts. Alternatively, they may also produce the compound “’de novo”.
Males of many species of Notoxus are attracted experimentally by cantharidin and these species eat and sequester the compound, with highest titres found in the testes. In these species, cantharidin is also found in “notches”’ located at the apex of the elytra (the modified, tough forewings that characterize the Coleoptera). Female Notoxus consume the compound, apparently using the notches as “test organs” for assessing the level of cantharidin in a potential mate. Females will not mate with males that have no cantharidin in their notches. Acceptable males have high levels of cantharidin in their notches and, especially, their testes, and the compound is transmitted to the female during copulation. Following copulation, a high concentration of cantharidin is found in the seminal vesicle of the female. The female later secretes it into her eggs, offering protection from predation to the eggs and larval stages of the beetle. There’s a lot going on in these little beings.
Credits: Dr Robert Copeland