Aphids increase their rate of survival on emergent aquatic plants through niche construction

Flooding or rain is a threat to many insects in nature, including herbivorous invertebrates whose hosts are emergent aquatic plants. They may thus have developed particular adaptations to withstand the flooding that is a feature of emergent plants' environment. The aphid Hyalopterus pruni (Hemiptera: Aphididae) modifies the physical and chemical conditions of its habitat by periodically spreading wax around itself with its hind legs. This behaviour constitutes a form of niche construction. We hypothesized that the aphid decreases its risk of death of own or around other individuals when submerged in water by spreading wax powder secreted from its body onto the leaves of its host plant, Phragmites australis. We compared the hydrophobicity of waxed and normal leaf surfaces. Next, we compared the survival rates of wax-powdering and nonwax-powdering aphids under submerged and rainy conditions in the laboratory and in the field. Finally, we examined whether the aphids' wax-powdering behaviour increased as a result of experiencing brief submergence or rain. The surface of the waxed area was significantly more water-repellent than the surface of unwaxed leaves. The waxed areas held air bubbles when under water. In experiments, aphids without wax around themselves exhibited lower survival rates: 22.9% in laboratory conditions and 15.7% in field conditions after 48 hr underwater. In contrast, aphids that secreted wax had higher survival rates, with 41.5% and 38.2% under laboratory and field conditions, respectively, after the same duration. Aphids exposed to rainfall showed similar results. Moreover, aphids that had experienced rain or submersion for 24 hr engaged in increased wax-powdering behaviour. These results indicate that aphids reduce their risk of drowning by powdering secreted wax onto the surface of leaves around them. Our findings suggest that niche construction by herbivorous invertebrates supports their ability to utilize host plants that grow under stressful conditions, such as emergent plants that are subject to periodic inundation.