In 1984, the wild passion fruit species Passiflora foetida, a plant native to Central and South America, was introduced to Australia. Its rapid growth allows it to form dense mats that cover trees and shrubs and smother the vegetation growing underneath. Over time, it became a serious environmental problem because it spread across large areas of the north of the country.
Today, in northwestern Australia, this invasion threatens patches of tropical rainforest in the Kimberley region and monsoon vine thickets on the Dampier Peninsula, ecosystems that are important for conservation, according to the Commonwealth Scientific and Industrial Research Organisation (CSIRO). But a Colombian bug unknown to science and a weevil recently found in the South American country could also help solve the problem.
The bug belongs to the species Pronotacantha maculata, described for the first time to science. It is only 3 mm long, has disproportionately long and slender legs, and small dark spots, reports the News Agency of the National University of Colombia (UNAL), Unimedios.
A Bug That Resembles a Mosquito
The insect belongs to the Berytidae family, whose members are known as stilt bugs because they resemble small mosquitoes. The Latin term ‘maculata’ means “spotted,” referring to the markings the insect has on its legs, and another of its characteristics is a pointed projection on its thorax.
The specimens were collected at the UNAL Agrarian Station Cotove, at the Medellin campus, in a tropical dry forest ecosystem, as well as at other locations in the departments of Antioquia, Cesar, Cordoba, Magdalena, and Sucre.
In addition to identifying the new species, researcher Alejandra Clavijo, who holds a doctorate in Biotechnology from the UNAL Medellin campus, described for the first time what this bug looks like during one of its developmental stages, before reaching adulthood. Her record expands the scientific information available on this group of insects.
Meanwhile, the weevil Philonis inermis, from the Curculionidae family, has a compact, robust black body covered with beige and reddish-brown scales that form transverse stripes across the elytra, that is, the hardened forewings that protect the second pair of wings.
Unlike the bug, this weevil was already known in other countries in the Americas, although its presence had not been documented in Colombia. The first specimens studied were collected in dry forest areas near Caucasia (Antioquia), and its presence was subsequently confirmed in locations in Antioquia, Cordoba, and Bolivar.
“Colombia has a very wide diversity of insects, but there are still many species and ecological relationships that we do not know about,” Clavijo explained, as quoted in the Unimedios bulletin. “Finding a new species for science and documenting the presence of another for the first time in the country allows us to expand this knowledge and better understand how these organisms interact with their environment.”
Study of Their Potential as Biological Control Agents
Identifying the two species required a process that combined fieldwork with laboratory analyses, since the study arose from the need to find natural enemies of wild passion fruit, which has become an invasive species in Australia.
Thus, the objective of the study was to identify herbivorous insects associated with Passiflora foetida and study their relationship with the plant to assess whether they could become potential allies in controlling its spread in the Oceanian country.
During their visits to the regions studied, the researchers observed the insects feeding on the plant and collected specimens to determine which ones might have potential as biological control agents. They examined the physical characteristics of the collected specimens using microscopes and stereoscopes, taking measurements and comparing their forms with the scientific descriptions of known species.
The team also studied their genes to identify differences that cannot be recognized simply by observing their appearance. In the case of the bug, the spots on its legs, its length, and the pointed projection on its thorax made it possible to distinguish it from other similar species and confirm that it was a species new to science.
In the case of the weevil, the study included monitoring its development. During her survey of 33 locations in Antioquia, Cordoba, Sucre, Bolivar, Atlantico, and Magdalena, the researcher confirmed the presence of Philonis inermis in 12 of them.
Larvae were also found inside swellings known as galls on the passionflower stems. These structures form in plant tissues and, in this case, are associated with the insect’s development. The researchers collected specimens to study their life cycle under controlled conditions.
Additional Assessments Are Still Needed
This work made it possible to describe the different stages of their development—egg, larva, pupa, and adult—and document aspects of their biology that were previously unknown. By comparing their characteristics with previous scientific descriptions, the researchers confirmed that it was a species known in other countries in the Americas, but whose presence had not been documented in Colombia.
“Although at first glance they are very similar species, they have differences that in many cases can only be clarified through their DNA, for example. We studied the genes of these organisms to find variations that could not be identified morphologically,” the researcher explains.
Australia’s CSIRO established a collaboration with researchers at the UNAL Medellin campus to search for insects in the plant’s native range that feed on it and could help regulate its populations.
The laboratory tests sought to determine whether the insects could feed on the invasive passionflower without damaging other plant species. To this end, the researcher evaluated the weevil’s response to five passionflower species, some cultivated and others native.
In one test, the insects had access to only one plant species; in another, they could choose between the invasive plant and one of the other species. Each trial was conducted over one week, and signs of feeding and egg-laying were observed. In all five replicates of the choice tests, the weevils fed and laid their eggs exclusively on Passiflora foetida.
In the tests in which they had no choice, no signs of egg-laying were recorded on the other plants, and only superficial feeding marks were observed on one of the species evaluated.
In addition, during their fieldwork, the researchers examined 250 specimens of the invasive passionflower and found that 75 had galls on their stems (structures associated with the development of weevil larvae), meaning that 30% of the plants examined were affected.
This research competed against more than 30 doctoral theses in the Three-Minute Thesis Competition, and its results show a marked preference by the weevil for the plant studied, although additional assessments are required before determining whether it can be safely used to control its spread in Australia without affecting other plant species.