Which insect is attracted to yellow sticky cards and may even be controlled by placement of enough cards?

The correct answer is that fungus gnats are attracted to yellow sticky cards and can be managed through their strategic placement. These insects are often found in moist soil and decaying organic matter, which makes them a common pest in greenhouses and indoor plant situations. Yellow sticky cards provide a visual cue that attracts the adult fungus gnats, as they are drawn to the yellow color.

By placing sufficient numbers of these sticky traps in areas where fungus gnats are prevalent, you can physically capture them, reducing their population and minimizing the potential damage to plants. The simplicity of this control method makes it effective for monitoring and managing fungus gnat infestations in a non-chemical way, which is especially beneficial in settings where pesticide use is limited or undesirable.

In contrast, other insects listed do not respond to yellow sticky cards in the same manner or do not rely on visual cues for attraction. For instance, German cockroaches typically seek out darker environments and would not be effectively managed with this approach. Moth flies and phorid flies have different environmental preferences and behavior patterns that do not align with the effectiveness of yellow sticky traps for control. Thus, the focus on fungus gnats highlights their unique attraction to this control method.