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The soil remained too wet for too long. It is best to make sure that there is plenty of drainage, and that you only water when the top of the soil is almost completely dry. This will keep the problem from happening again in the future.

It appears to be wilting, from inadequate water. But rule out insect pest activity by inspecting the underside of the leaves. Some sucking insect pests like aphids will cause leaf curl like in the first photo.
Get a soil moisture meter to take the guess work out of watering. https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm

I had a family member with the same issue, and the problems were lack of light and needing fertilization. These are the most common reasons for the leaves to drop from the plant. You may use a half strength fertilizer just a few times per year, and make sure that the plant remains in a bright location with filtered sunlight. Direct sun can be a bit over-bearing for the plant.

Here is an article for more information on the care of the plant: https://www.gardeningknowhow.com/houseplants/schefflera/schefflera-plant-care.htm

Without know the type of pest that you are referencing; Neem Oil would be a good treatment.
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

This could be happening for a number of reasons. Could you include some more information about where it located, how much light that it receives, how often it gets watered, and most importantly, photos? This will help me to give you the best advice on fixing the issue. This can occur for quite a number of reasons, so it is important to know some details.

This is likely from a pest infestation.
Treat with Neem Oil.

https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
https://www.gardeningknowhow.com/garden-how-to/info/what-is-honeydew.htm