Foliar nutrients explain goldspotted oak borer, A grilus auroguttatus , adult feeding preference among four C alifornia oak species

Adults of the invasive goldspotted oak borer, A grilus auroguttatus S chaeffer ( C oleoptera: B uprestidae), consumed foliar weight in no‐choice feeding tests of, in descending order, C alifornia black oak Q uercus kelloggii N ewb., E ngelmann oak, Q uercus engelmannii G reene, coast live oak, Q uercus agrifolia N ée, and canyon live oak, Q uercus chrysolepis L iebm. ( F agaceae). Furthermore, significantly more foliar area was consumed of Q . kelloggii than of Q . chrysolepis . In dual‐choice feeding tests with isolated leaf disks, A . auroguttatus consumed significantly more foliar weight and area of Q . kelloggii relative to the other three oak species, and more foliar weight of Q . agrifolia than of Q . chrysolepis . In dual‐choice feeding tests with leaves on small branches, A . auroguttatus consumed more foliar weight of Q . kelloggii than of Q . engelmannii and Q . agrifolia . Thus, multiple experiments suggested that adults of A . auroguttatus preferred the foliage of Q . kelloggii over that of the other three oak species, and among the other three species they did not appear to have a strong feeding preference. Factor analysis reduced the quantities of 13 foliar nutrients into two new variables (factor 1 and factor 2). Factor 1 was weighted heavily on the quantities of nitrogen, sulfur, phosphorus, potassium, zinc, and copper, whereas factor 2 was weighted heavily on the quantities of zinc, iron, and aluminum. Factor 1 varied by oak species, with Q . kelloggii having a higher factor 1 nutrient content than the other three species. Factor 2 response was higher in Q . kelloggii , Q . agrifolia , and Q . engelmannii than in Q . chrysolepis . The collective effects of four macronutrients (nitrogen, sulfur, phosphorus, and potassium) and two micronutrients (zinc and copper) suggest that these might be the nutrients directing preferential feeding of A . auroguttatus adults on the foliage of Q . kelloggii . Leaf toughness might also play an important role in feeding preference. Female A . auroguttatus did not show an ovipositional preference among the four oak species.