A recent investigation carried out by Italian researchers, and published in the scientific journal Entomologia Generalis, has revealed that the Tuta absoluta pest that ravages tomato crops in the Mediterranean basin is capable of transmitting the tomato brown rugose fruit virus.

The tomato is one of the most important horticultural crops in the world, with more than 5 million hectares and a total production, according to FAO data in 2022, of more than 186 million tons, with Italy being one of the main European producers, hosting 38% of European production. A crop that is constantly threatened by numerous arthropod pests such as Tuta absoluta or South American tomato pinworm, among others such as whiteflies, aphids and thrips, relevant for their ability to transmit plant pathogens.

In this context, since 2014, when its discovery was reported by several countries in the Mediterranean basin, the tomato brown rust virus (ToBRFV) represents one of the most important threats to tomato crops worldwide, and is currently widely distributed with outbreaks in Europe, Asia and America. Its transmission occurs mainly through contact between plants and infected surfaces, and only one case of mechanical transmission by arthropods, such as bumblebees at the time of pollination, had been described. Furthermore, the virus, in addition to tomato, pepper and other solanaceous crops, infects some grasses, so weeds can be a reservoir of the virus throughout the growth cycles of tomatoes.

Being an extremely infectious virus, ToBRFV spreads very quickly in fields and nurseries and is classified as a seed-borne virus. However, transmission occurs through direct contact between plants, including propagation material, through small wounds in transplanted seedlings, and through infected sap that contaminates different surfaces. In this regard, until the time the research began, there was no scientific evidence of the transmission of the tomato brown rugose fruit virus by arthropods, except for bumblebees, so the researchers wanted to check whether a key pest such as Tuta absoluta in tomato crops can transmit the virus, since its host area mainly includes Solanaceae species and it lays its eggs in a wide range of wild and cultivated plants from other families.

To this end, in the environment of the Research Centre for the Protection and Certification of Plants (CREA), in Italy, healthy tomato plants obtained from tomabovirus-free seeds grown in isolated cages to avoid accidental infections and infestations were subjected to mechanical inoculation of ToBRFV from the Sicilian isolate (from the first discovery of the virus in Italy, dated 2018), and once the positive result of the virus infection was confirmed, one hundred newly emerged Tuta absoluta adults were released from the pupa without determining the sex, allowing the moths to lay eggs for 72 hours, and then removing them.

Laboratory tests demonstrated the presence of ToBRFV in adult moths obtained from larvae developed in plants infected with the tomato brown rugose fruit virus, while they were able to infect healthy tomato plants.

Therefore, the researchers evaluated whether the presence of ToBRFV in adults was internal or external to the pupae, derived from their feeding in the larval stage on infected plants. To do so, they analyzed adults obtained from both disinfected and non-disinfected pupae, and all tested positive for the virus, suggesting that the presence of the virus is on the internal surface of the pupal cover (exuvia), and the contamination of the specimens during their emergence from it, since, when analyzing the hemolymph of the adults (the equivalent of blood in invertebrates), no trace of the virus was found, so the presence of the virus in these specimens was not internal, but external.

Therefore, they concluded that the transmission of ToBRFV from these adults to healthy plants may be due to the contact of these infected individuals with wounds present in the plant, preexisting or inflicted by the pest itself. Which, taking into account the high mobility of this pest, together with the different and efficient modes of transmission of the virus, suggests that Tuta absoluta could be responsible for the spread of the virus between crops and its persistence throughout the different crop cycles.

Something that leads researchers to warn that, in tomato cultivation systems such as the protected one, widely developed in the Mediterranean area, where the movement of arthropods and diseases occurs not only in the internal and external areas of greenhouses, but also between crops, greenhouses, and where the management of the Tuta absoluta pest is carried out mainly through integrated pest management based on biological control, and taking into account that this biocontrol system has not proven efficient in controlling viruses, it should be evaluated whether the natural enemies of this pest could also be involved in the spread of the virus, especially from plant to plant, especially in omnivorous ones, such as mirid bugs, and adapt the integrated pest management strategies for the control of Tuta absoluta to the simultaneous presence of the virus.