Zabrus tenebrioides

Zabrus tenebrioides

The humpbacked beetle (Zabrus tenebrioides Goeze, 1777) is a beetle belonging to the Carabidae family.

Systematic –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Subkingdom Eumetazoa,
Bilateria branch,
Phylum Arthropoda,
Subphylum Tracheata,
Superclass Hexapoda,
Class Insecta,
Subclass Pterygota,
Endopterygota cohort,
Superorder Oligoneoptera,
Coleopteroidea section,
Order Coleoptera,
Carabidae family,
Subfamily Pterostichinae,
Zabrini tribe,
Genus Zabrus,
Species Z. tenebrioides.
The term is basionymous: Carabus tenebrioides Goeze, 1777.
The terms are synonymous:
– Attelabus fossor Fabricius, 1781;
– Blaps tenebrosus Fabricius, 1801;
– Buprestis piger Geoffroy, 1785;
– Buprestis pigra Geoffroy, 1785;
– Carabus gibbosus Marsham, 1802;
– Carabus gibbus Fabricius, 1794;
– Carabus madidus Olivier, 1795;
– Scarites fossor (Fabricius, 1781);
– Zabrus ciscaucasicus Lutshnik, 1928;
– Zabrus cyprensis Freude, 1988;
– Zabrus elongatus Ménétriés, 1832;
– Zabrus gibbosus (Marsham, 1802);
– Zabrus gibbus (F., 1794);
– Zabrus hispanus Freude, 1988;
– Zabrus longulus Reiche & Saulcy, 1855;
– Zabrus piger (Geoffroy, 1785);
– Zabrus tenebricosus (Goeze, 1777);
– Zabrus tenebrioides subsp. cyprensis Freude, 1988;
– Zabrus tenebrioides subsp. hispanus Freude, 1988;
– Zabrus tenebroides (F., 1794);
– Zabrus tenebrosus (Fabricius, 1801).

Geographic Distribution and Habitat –
Zabrus tenebrioides is a beetle widespread in much of Europe; in Italy it is present in all regions, especially the central-northern ones. It is usually found on cereal plants such as wheat, barley and rye, but in the absence of the latter it can also be found on spontaneous grasses.

Morphology –
The Zabrus tenebrioides is a small Carabidae, between 15 and 18 mm long, brown-black in colour, with a dorsally convex body (for this reason called humpback), oval in shape.
On the elytra it has evident longitudinal furrows.
The legs are cursorial type.
The larvae are about 25-30 mm long, have a flattened body, with a brownish head, thorax and dorsal part of the abdomen; the remaining part of the body is yellowish-white in colour.

Aptitude and biological cycle –
The life cycle of Zabrus tenebrioides lasts one year, of which the larval stage occupies the winter months. The adult can be found in the fields towards the end of May, beginning of June.
In an initial phase of their growth they generally remain hidden in the ground, under clods or tufts of grass, and then climb up the plants during the night in search of caryopses. In the second phase of their development they also become active during the day, sometimes making long journeys in flight.
In August-September, upon reaching sexual maturity, they mate, following which the female specimens bury themselves to lay around sixty eggs.
After an incubation period of 2 weeks, the young larvae emerge from the eggs and remain in the ground for more than a month without feeding, after which they move to the edible parts of the plants to begin their feeding activity which reaches its peak in spring, when the the same larvae are brought to the foliage to feed at the expense of the leaves.
After going through three stages of larval development, towards the beginning of April, they mutate into prepupa and then into pupa inside an oval-shaped cell located in the ground at about 15-20 cm deep. This pupal stage lasts on average 2 to 3 weeks, at the end of which the adult appears.

Ecological Role –
Zabrus tenebrioides is not a predator, unlike the other species belonging to the Carabidae family. This beetle mainly attacks roots and kernels of wheat, but we can also find it in fields sown with barley or in soil with spontaneous grasses. Causes erosion of leaves, roots and ears.
The damage occurs only in certain years, it occurs on the caryopses (adults), on the roots and on the basal leaves (larvae).
The adults, who have crepuscular habits, come out of their daytime shelters and climb the plants (they are not equipped with functioning wings) to feed on caryopses.
The larvae that live in the soil are particularly harmful, as they feed on the roots of young plants in autumn and on the basal leaves in spring. The larvae dig tunnels in the ground from which, protruding their mandibles, they grasp the basal leaves; at the base of the plants, at the entrance to the tunnels, there are accumulations of leaf residues which are gradually frayed.
In the case of high populations of this insect, until now the fight has been of a chemical nature and has only been carried out when damage appeared. Furthermore, the geodisinfestations carried out for Noctaceae and Elaterids also highlight a collateral activity of containment of the phytophagous.
However, as with other biocenoses, the containment of these insects must be prevented with the adoption of agroecological systems, less specialization of crops, greater intercropping and less use of external inputs.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Russo G., 1976. Agricultural Entomology. Special Part. Liguori Editore, Naples.
– Pollini A., 2002. Manual of applied entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.

Photo source:
– https://inaturalist-open-data.s3.amazonaws.com/photos/304867739/original.jpeg