Do natural mosquito deterrents affect beneficial insects?

Asked June 17, 2020, 8:00 AM EDT

I want to help the environment as much as possible with my yard, so I’ve planted natives, certified the yard with NWF, planted a pollinator garden, do not use chemicals, etc. Mosquitoes have been a big problem in the past, but now I’ve removed all sources of standing water. I have planted an army of herbs that supposedly deter mosquitoes. I make a homemade spray from catnip, mint & other herbs, then add citronella & geranium oil. I spray this around the patio and along the shady fence lines. I do not want to deter pollinators though. I’ve spent a lot of time searching the internet but can’t find the answer. Do the herbs that deter mosquitoes also affect pollinators? Thank you.

Prince George's County Maryland

1 Response

Encouraging species diversity as you are is not only good for the environment but helpful in mosquito control, as multiple insects and other animals feed on mosquitoes as part of their diet. By giving these organisms alternative food sources throughout the year, they are more likely to be present when mosquitoes are flying.

There is lots of good information on mosquito control on this page, which you may have already found through your own research: https://extension.umd.edu/hgic/topics/controlling-mosquitoes

Home remedies and scented plants are not scientifically proven to be consistently effective in repelling mosquitoes. Extracts isolated (and possibly concentrated) from various strongly-scented plants have shown some mosquito-repellent qualities (though measurably less than laboratory formulations like DEET), but their presence locked inside living, uncut plants is unlikely to have any measurable impact.

Most plants have an array of defensive compounds, some of which smell pleasant to us, but they are sequestered inside the plant tissues and an insect isn't going to get exposed unless feeding on that plant. (Hence, most deter herbivory.) Mosquitoes could probably land on one of these repellent plants directly and not be affected. Crushing the leaves and rubbing them on skin, for instance, might be more impactful in keeping mosquitoes at bay. (However, this is not ideal, because you never know what dose or secondary chemicals you're exposing yourself to; this is why commercially-processed formulations are more reliable and purified.)

Multiple sensory elements draw mosquitoes to humans to bite; using body odors is only one. Carbon dioxide, body heat, and visual cues also play a role, and carbon dioxide seems to be the initiating factor. Since we cannot control this, we rely on repellents to discourage them from landing or to confuse their scent detection so it's more difficult to locate us.

As to whether the herbal repellents deter pollinators...that is uncertain. Presumably, since these are defensive plant compounds, they may deter at least some insects, pollinators or otherwise. Some plant oil extracts are even used as organic insecticides, so avoiding unnecessary spraying would be best. If you are only spraying hard surfaces and not living plants, this may have little detriment. Use caution with plant contact with your homemade spray - since oils and water do not mix, presumably the recipe includes a surfactant to get the two to blend. Such compounds can also damage plant tissues or remove their protective waxy leaf coatings. Temporary phytotoxicity (essentially plant chemical burns) may result.

In general, we do not recommend broadcast/area sprays of any type for mosquito control. Doing what you were already doing - encouraging beneficial predators and removing breeding sites - plus using personal protection (repellents, long clothing) is the best multi-pronged approach.

Miri