Certain wasps and bees exhibit the remarkable ability to identify unwell nestmates by scent, preventing their entry and safeguarding the entire colony from infection, ensuring the species’ long-term survival. However, a study detailed in the journal Environmental Science and Pollution Research reveals a divergence in this recognition mechanism for paper wasps of the Mischocyttarus metathoracicus species when infected with a biopesticide based on the fungus Beauveria bassiana.
Led by researchers at the University of São Paulo’s Ribeirão Preto School of Philosophy, Sciences and Letters (FFCLRP-USP) in Brazil, the study utilized molecular, survival, and behavioral assessments. Findings indicate that the biopesticide not only proves fatal to the wasps, crucial for pest control and pollination, but also eludes detection by nestmates.
André Rodrigues de Souza, a researcher at FFCLRP-USP and the article’s corresponding author, emphasizes the contrasting effects of the biopesticide and a synthetic insecticide (imidacloprid). While the synthetic insecticide can rapidly decimate entire wasp colonies within 24 hours, the biopesticide, while initially less lethal, extends its impact over 19 days, posing a potential threat to the long-term survival of the species.
Crucially, the biopesticide stands out due to its composition, housing spores of the fungus B. bassiana, exclusively infecting insects and sparing mammals and other animals. In comparison, the synthetic pesticide tested in the study, widely used and highly toxic to mammals, underscores the importance of proper handling to avert harm to humans.
Defensive behavior
In the survival experiment, approximately half of the wasps exposed to the biopesticide succumbed to its effects, while the entire group exposed to the synthetic compound faced mortality. Notably, the imidacloprid-based pesticide, despite being 50 times less concentrated than the biopesticide, demonstrated significantly higher toxicity to these insects.
A control group subjected to an inert product or water experienced less than a quarter of wasp fatalities, underscoring the pronounced lethality of both pesticides.
In behavioral assessments aimed at determining whether wasps infected by the fungus were recognized by nestmates, researchers employed deceased wasps as lures on sticks. These lures were brought near the nest, allowing resident wasps to interact physically with them. The resident wasps exhibited the ability to distinguish nestmates from individuals belonging to other nests, displaying aggression through biting and stinging.
Recognition relied on detecting the odor of cuticular hydrocarbons, chemical messengers present on the surface of these insects’ bodies and used for communication. Given the competitive nature of this species, nest invasions are commonplace, met with vigorous defense.
Interestingly, nestmates infected by the biopesticide, bearing fungal spores on their bodies, continued to be accepted by the colony. Souza emphasizes that if the infected nestmates were also attacked, the biopesticide wouldn’t pose as much of a threat. However, their admission into the nest, coupled with the 19-day period of coexistence with the fungus, raised concerns about the potential transmission of spores, posing a risk to other adults and larvae and potentially jeopardizing the entire colony.
Threatened allies
The biopesticide, laden with numerous fungal spores, is systematically sprayed on crops, enabling the fungus to infiltrate and eliminate various pests like caterpillars, coffee borer beetles, red spider mites, eucalyptus weevils, and silverleaf whiteflies. These pests pose threats to a diverse range of crops, making the biopesticide a targeted solution.
Wasps, integral allies in the biological control of pests, primarily feed on caterpillars. Additionally, these social insects play a crucial role as pollinators for both cultivated crops and wild plants.
According to Souza, the study’s outcomes emphasize the need not to dismiss the use of biopesticides but to subject them to rigorous testing equivalent to synthetic pesticides and manage their application thoughtfully. One practical consideration is avoiding daytime application when the wasps are actively foraging, potentially carrying spores back to their nests.
Recent research underscores the inadequacy of relying solely on mortality assessments to evaluate the safety of pesticides, be they synthetic or biological, for non-targeted species. Some compounds may not cause immediate fatalities but can lead to issues like loss of fertility, impacting the species’ long-term survival. Building on these findings, researchers are now exploring the impact of an essential oil widely used as a biopesticide on wasp fertility, recognizing the importance of comprehensive evaluations beyond immediate mortality effects.
Source: FAPESP