There are several ways to kill mealybugs instantly, including:

1. Isopropyl Alcohol: Soak a cotton ball with 70% isopropyl rubbing alcohol and wipe it on the mealybugs on the plant. Be sure to test it on one leaf before applying the alcohol to the whole plant to ensure the alcohol doesnt burn it.

2. Insecticidal Soap: Insecticidal soaps applied directly on mealybugs can provide some suppression, especially against smaller infestations.

3. Neem Oil: Mix neem oil, which is an organic insecticide, and spray it on the plants in the morning or evening.

4. Predatory Insects: Lace bugs, parasitoid wasps, and a beetle known as the mealybug destroyer can naturally kill mealybugs. Introduce predatory insects to your garden by planting host plants that attract them, or purchase them from commercial online retailers.

5. DIY Spray: Combine a bulb of garlic, a small onion, and 1 teaspoon of cayenne pepper in a blender and blitz into a paste. Next, add 1 quart of water. Alternatively, fill a spray bottle about a 1/4 of the way with rubbing alcohol, add a good glug of insecticidal soap, plus a 1/4 tsp of Neem oil if you have it. Fill the rest of the way with hot water and shake well and often. Apply very thoroughly to all plants (including ones that dont yet appear to be infected), with special attention to any crevices and leaf joints. Repeat every week to 10 days, at least two or three times.

Its important to note that while these methods can kill mealybugs instantly, they may not be effective against heavy infestations. Its also recommended to inspect new plants thoroughly for mealybugs before bringing them into your home, and to maintain healthy, vigorous plants to prevent infestations.