Experimental evaluation of metarhizium-treated baits as a biological control strategy against locusts

Locusts pose a major threat to food security due to their exceptional mobility and voracious feeding behavior. While synthetic pesticides are effective, their negative impacts on the environment, human health, and non-target species highlight the need for safer alternatives. Biological control agents like Metarhizium acridum offer a promising, environmentally friendly solution, but challenges such as slow action and sensitivity to environmental conditions limit their effectiveness. Innovative delivery methods, such as bait formulations, may enhance fungal performance by attracting target species and increasing spore contact. This study assessed the efficacy of Metarhizium-treated baits for controlling the Central American locust (Schistocerca piceifrons), a major pest in Mexico and Central America. We exposed locusts to bait treated at 5, 20, and 60 kg/ha in large mesh cages for two days, while providing ad lib access to untreated local vegetation. Mortality was recorded daily over seven days, and cadavers were examined for fungal sporulation. The 60 kg/ha treatment produced the highest mortality. Over 60% of cadavers showed fungal growth, confirming Metarhizium infection. We also tested bait attractants (banana, vanilla, sugar) to assess attractiveness and potential effects on efficacy. Behavioral observations showed a preference for banana-flavored bait, suggesting its potential use as an attractant. However, individual feeding trials revealed lower mortality among locusts that consumed banana- and vanilla-flavored baits, possibly due to interference with spore viability. These results support bait formulations as a viable delivery method for Metarhizium, while also highlighting the need to consider how flavor additives may affect fungal efficacy.