What is the origin of agricultural insects?

Insects such as beetles bore holes in the trunk of a tree to make a gallery in the wood to protect their spawn. As it burrows the tunnel, it scatters ragweed fungus spores that will feed the larvae.

When they drill into another tree, the adult beetles will be vectors for transmitting the fungus spores to a new habitat. This mutualism between insects and ragweed fungi could be more than 100 million years old – much older than previously thought – according to an article published in the journal Biological Reviews.

The work analyzes for the first time the symbiotic relationship and co-evolution between beetles and ragweed fungi from a paleontological perspective, and it does so through the Cretaceous fossil record of these biological groups. The authors of the study are the experts David Peris and Xavier Delclòs, from the Faculty of Earth Sciences and the Biodiversity Research Institute (IRBio) of the University of Barcelona, ​​and Bjarte Jordal, from the University of Bergen (Norway).

Fungus-growing beetles millions of years before human agriculture

For millions of years, some termites, ants and cockroaches have been able to grow fungi to feed themselves. This mutualism between insects and fungi -one of the best studied symbioses in the natural world- is an evolutionary strategy analogous to the agricultural activity of the human species, which has existed since the Neolithic revolution.

Understanding the origin of the symbiosis between insects and fungi is a field of interest in various scientific disciplines. Currently, the mutualism between beetles and symbiotic ragweed fungi is the cause of pests in forests and crops that generate serious ecological and economic losses. Nevertheless, «The ecological factors that gave rise to this food strategy are still not well understood, nor how it became a symbiotic relationship with forced dependence»explains David Peris, first author of the article.

When did the lineage of agricultural insects begin?

Traditionally, phylogenetic studies suggest that beetle fungiculture began more than 50 million years ago – much earlier than in other insects – and some studies even date it to around 86 million years ago. “It is likely that the symbiotic relationship between fungi and cockroaches originated more than 100 million years ago, during the Lower Cretaceous, in groups of cockroaches that had gone unnoticed until now”David Peris now reveals.

As part of the research, experts have studied various specimens of biological groups captured in Cretaceous amber from around the world. Thus, the origin of ragweed fungi is older than the main beetle groups of the subfamilies Scolytinae Y Platypodinae -family Curculionidae- that today grow mushrooms on tree trunks, the authors point out.

“This indicates that these fungi used some other group of insects to disperse millions of years ago”Peris points out. “In addition, other groups of beetles with similar behavior to ambrosia beetles -family Bostrichidae and above all Lymexylidae- they present an abundant older fossil record that would coincide with the appearance of ragweed fungi, according to other previous studies».

“The most interesting of all -continues the expert- is that some works cite the ability to cultivate fungi in some of these current species».

Evolutionary convergence towards an obligate mutualism

The mushroom cultivation process begins when the beetles colonize a new tree trunk or branch. During the Cretaceous, the abundance of wood fungi and cockroaches led to an initial domestication of some groups of fungi.

Initially, fungal spores were accidentally carried from tree to tree by borer beetles, “until this mutually beneficial association evolved into a more intimate symbiosis in which the fungi were transported to a tree, the fungal mycelia grew, and the beetle larvae fed on the fungus”points out Bjarte Jordal.

This conjunction of factors, added to the high capacity of adaptation and change of the symbionts, facilitated the morphological and ecological adaptations of the biological groups that converged evolutionarily in an obligate mutualism. That is to say, a symbiotic relationship between insects and fungi of a beneficial nature for both organisms that still endures.

“However, it will be necessary to deepen the knowledge about the ecology of the species of the families Lymexylidae and Bostrichidae to obtain more concrete conclusions. Therefore, the discovery of new fossils in Cretaceous amber from these biological groups will undoubtedly help to better interpret the evolutionary history of this symbiotic relationship that has survived to our days»concludes Professor Xavier Delclòs.

Font: UB, DICYT,

Reference article: https://www.dicyt.com/noticias/el-origen-de-los-insectos-agricolas