Spain (Canary Islands): ICIA evaluates natural enemies of the Guatemalan potato moth

The results,  published in the journal Phytoma , reveal that the parasitoid Trichogramma achaeae is effective in field conditions, while the predatory mite Blattisocius tarsalis is effective in storage.

The Guatemalan potato moth, which arrived in Tenerife in 1999, is causing huge economic losses in the Canary Islands. It causes damage to plots, where it can affect up to 50% of the harvest, and in storage, where it can spoil the entire harvest. In addition to production losses, the severity of the pest is also contributing to a reduction in the area under cultivation and an increase in costs resulting from its management. “If this pest is not controlled, there could be a collapse in local potato production, as well as possible losses of historically important cultivars,” warn the authors of this study, Jorge Gavara, Estrella Hernández-Suárez and Ana Piedra-Buena. In 2022, this crop represented around 10% of the total agricultural production in the Canary Islands, with an approximate production of 111,208 tonnes and an area of ​​4,014 hectares.

In the field, phytosanitary treatments and cultural measures are not effective against this quarantine pest, and there are currently no authorized insecticide treatments in storage for its control. In this context, the search for natural enemies for biological control has become particularly important, especially those specialized in eggs, which cause the death of the insect before the larvae are born and prevent damage.

To determine their suitability as biological control agents, ICIA researchers evaluated the parasitoids Trichogramma euproctidis and T. achaeae, as well as the predatory mite Blattisocius tarsalis.

Tecia solanivora produces significant losses both in the field and in storage.

Trichogramma egg parasitoids are successfully used for biological control of a wide range of Lepidoptera worldwide. In this study, T. euproctidis, despite favouring the reduction of the Guatemalan moth population, failed to obtain healthy tubers under field conditions. T. achaeae was able to reduce damage and obtain healthy tubers. This parasitoid “proved to be a biocontrol candidate suitable for testing in cultivation, where higher release densities and a greater number of releases should be considered,” the researchers emphasise.

Under storage conditions, both parasitoids were ruled out: T. achaeae was unable to parasitize without light, while T. euproctidis did not achieve significant protection of the tubers. On the contrary, B. tarsalis did, although the researchers point out that it can only prey on eggs on the surface of potatoes: “Once hatching occurs and the larva penetrates the tuber, it is inaccessible to the mite, so its application does not exempt the correct visual control of infested tubers prior to storage.”

The research group wants to continue working with these biological control agents to study “the adaptation and standardisation of their use in real conditions, the adjustment of release densities and number of releases, as well as verification in other storage systems and economic viability”.