Allograpta aenea belongs to a group, subgenus Rhinoprosopa, characterized by: face greatly produced anteriorly, with low indistinct tubercle or no tubercle; oral opening about 5.5 times as long as wide, with oral apex greatly extended beyond level of antennal base; antennal pits distinctly separated; plumula absent; subscutellar pile fringe absent; wing microtrichose, without apical dark macula; alula absent or narrow, less than 1/2 as wide as cell BM; metasternum bare; abdomen narrowly to strongly petiolate (Mengual et al. 2009).
Allograpta aenea differs from other species in this group by: scutellum and anepimeron pale; katepimeron yellow and katatergum almost completly yellow.
Adults are pollinators and feed on pollen and nectar.
Adapted from original description (Hull 1937).
Head. Eyes bare, the vertex narrow, rapidly widening to the level of the antennae, where the face is parallel-sided and rather narrow. In profile the head slants down from the vertex quite straight to the low tubercle shortly below the antennae and is then still further produced to the epistoma, though not quite so sharply. Face, because of the narrowness, with a pinched out aspect. Gena pale brownish yellow, the sides of the face bright shining yellow. Frontal triangle rusty orange, black macula above antennae and facial black vitta. Vertical triangle bright yellow. Antennae set very far apart, short; basoflagellomere a little longer than wide. Arista as long as the antennae. Occiput not visible from the side below the middle of the eyes.
Thorax. Scutum as wide as head, quite convex, both from the front and from the side very sparsely pilose. Postpronotum bare, scutellum large, semicircular, somewhat flattened, a few large bristles on the margin, a few downward projecting hairs, but scarcely any fringe. Legs. Femora short, straight, scarcely thickened. Tibiae distally a little thickened and a little pinched, every bit as long as the femora. Wing. Wings considerably longer than abdomen, very brown, darkened apically with a dark brown stigma. Alula reduced. M1 vein close to wing margin, but very sigmoid. Vein R4+5 and costa carried down somewhat deeply at the end of the wing. Vena spuria heavily chitinized.
Abdomen. Abdomen reddish brown, basal and apical borders of the remaining terga broadly shining, but preceded by opaque fascia, which are produced forward as a slender triangle as far as the base of the tergum. Abdomen slender, spatulate, about five times as long as its greatest width, which begins on the fourth tergum. Fourth and fifth terga with practically parallel sides. Second tergum apically about two-thirds as wide as the fourth tergum. Sides of the short first tergum convex with stiff bristles. Margins of the abdomen curling over, especially posteriorly, where they decrease the width some.
Allograpta aenea was included in the molecular anlysis of Mengual et a. (2008a), and was resolved as sister group of Allograpta sycorax within the Rhinoprosopa clade; all of them as sister group of subgenus Costarica.
Very restricted, only collected in Costa Rica and Hispaniola Island.