No one knows the answer to my question about whether or not deer repellent also repels beneficial insects — that’s why I reached out to you.  I’ve sought the answer from numerous groups and experts, and no one can give me an answer.  

Ok, our apologies. Unfortunately, we don't think much research has been done on this topic. We will check with our entomologists and get back to you. Beneficial insects are a very diverse group, so even if one of the ingredients in a deer repellent product keeps them away from a treated plant for a limited period of time, we doubt it will have a significant impact on their host/prey-seeking or pollinating behaviors.

Miri

Our entomologists can look into this, but they agree that the impact (or not) on insects very much depends on what kind of deer repellant is used. Once they have a specific ingredient to reference, they can more easily look up what insects are known to be repelled by certain volatiles given off by that repellant, if it's known. However, they say that more than likely deer repellent overall won't be having a significant effect on beneficial insects.

Miri

Thank you for pursuing an answer for me.  I’m unable to fence my area so have to net the native plants that deer and rabbits eat.  At age 76 t’s a lot of work because I remove the netting on my garden slope daily to give access to insects and butterflies.  Some neighbors dislike the look of the netting so there’s that to consider as well.  I planted snakeroot because it’s poisonous but the plants were eaten anyway  I always assumed that the odor of repellents would confuse insects so never used them.  I hope that repellents I’ll use have no long term effect on beneficial insects.

We have a general response from one of our entomologists (copied below, though written before we received your most recent bit of information about the situation). We'll pass along any other information they share with us if they can get into any more detail. We realize you're trying some of these methods already, like growing plants that are supposed to be avoided by the deer. Sometimes, they'll eat new plantings as they explore or sample new things, and then leave them alone later once they're established. Sheltering individual new plants with a cloche of some sort (like a little cage...some gardeners secure wire mesh trash cans over the plant, if it fits) can help keep the deer off them for the first year in the ground as roots establish.

Thank you for reaching out to us and for your concern regarding beneficial insects. While natural deer repellents are generally considered lower risk than conventional pesticides, they may still have unintended effects on beneficial insects and other animals. Without knowing the specific product or ingredients being used, it is important to note that commonly used components such as garlic, cottonseed, or clove oil can impact non-target organisms. There is evidence that essential oils (depending on the concentration), particularly garlic oil, can affect honey bee foraging behavior and may be toxic to honey bee workers and larvae (juveniles) [research by Xavier et al. 2015]. There is still a lot we do not know about the non-target impacts of essential oil–based products, as many are not subject to the same standardized testing requirements as other registered pesticides.

If you choose to use a deer repellent, consider avoiding applications on pollinator plants, especially those that are actively flowering, as well as plants that may serve as hosts for caterpillars. High concentrations of essential oils could negatively affect insects and other animals. More research is still needed to fully understand these impacts.

The most important consideration when applying any commercial deer repellent is the product label. Always follow label directions carefully. Most repellents are recommended for application during the dormant season and should generally be applied on windless days when temperatures exceed 40°F.

For more information on managing deer and selecting deer “resistant” native plants, please see the following resources--
Managing Deer in Gardens:

• Using Commercial Deer Repellents to Manage Deer Browsing in the Landscape (PDF)
• Deer: Stay Out of My Garden! - Maryland Grows blog

Deer "Resistant" Native Plants:

• Deer Resistant Native Plants
• Deer Challenges and Deer Resistant Plants (see pages 38-40) - Maryland Native Plant Guide: Piedmont Region

I'll add that which plants to choose from will depend on how much direct summer sun the site gets, and how well-drained the soil is. If you're not already growing them, some plants with scented foliage that deer dislike, such as native Mountain-mints (Pycnanthemum, several species) and various perennial herbs (lavender, oregano, thyme) that are allowed to flower have blooms that are popular with pollinators, if the area is sunny and drains well. A variety of beneficial insects are not pollinators, since they get their food from sources other than flowers, but they still benefit from a landscape with a diversity of plant species, especially native species. Gardens can also be supplemented with non-native but non-invasive annuals whose flowers are appealing to pollinators, since some of them are also unappealing (usually) to deer. Most of the options in this category are sun-loving, and candidates include Lantana, Verbena, Salvia, and Zinnia.

Netting is certainly easier to move around as needed and less expensive to install than fencing, but the risk with using it is that other animals might become caught and injured in the mesh (snakes, lizards, birds, bats, squirrels, etc.) unless it's a very fine, close-knit material more like tulle than open-weave bird netting. (Bird netting and deer netting that's commonly sold as black plastic netting tend to be the same material and size.)

Deer don't have great depth perception, so not only can short or more minimalist fences and barriers work (if they can't tell how far over a double row of low fencing they need to clear), but they also don't like to jump over something if they can't see where they will land. Smaller enclosures where a fence encircles a small space also deter them, since they won't be able to get back out easily if they need to get a running start. Nothing is foolproof, of course, and we've heard stories of persistent deer probing a fence for a week spot they can push under or through, which might be a tactic they take with netting as well if they become desperate in looking for fresh foliage to eat.

We don't know if insect-repellent qualities have been found with other commonly-used deer repellent ingredients, such as putrescent egg solids and capsaicin (the spice in hot peppers). Not all butterfly and moth pollinators use the same plant they visit for nectar or pollen as host plants for caterpillars, so if you can avoid spraying blooms, you may be fine with regards to minimizing impacts on leaf-feeding insects.

Miri