Organic pesticides can take effect upon contact or through:

Organic pesticides can take effect upon contact or through ingestion, which is why the selection of "contact or ingestion" is the most accurate. Many organic pesticides are designed to work through various entry points, allowing them to be effective against pests in multiple ways.

When a pest comes into contact with an organic pesticide, it can absorb the active ingredients through its outer body surfaces, leading to immediate effects. In addition, if the pest consumes the pesticide through contaminated food or surfaces, the active ingredients can work internally to eliminate the pest. This dual mode of action—contact and ingestion—enhances the overall efficacy of these products in pest control strategies.

The other options are limited as they specify only one entry point—either skin, respiration, or consumption—which does not encompass the full range of how organic pesticides can act on pests effectively. Therefore, the broad applicability of the correct answer underscores the versatility of organic pesticides in pest management.