Defensive production of formic acid (80%) by a carabid beetle ( Galerita lecontei )

Abstract

The carabid beetle Galerita lecontei has a pair of abdominal defensive glands that secrete a mixture of formic acid, acetic acid, and lipophilic components (long-chain hydrocarbons and esters). Formic acid, at the concentration of 80%, is the principal constituent. The beetle ejects the secretion as a spray, which it aims accurately toward parts of the body subjected to assault. At full capacity, the glands store 4.5 mg of formic acid (3% of body mass), enough for upward of six ejections. The beetle reloads the glands at a rate of 126 g of formic acid per day. For the approximately 500 secretory cells of the glands, this means an hourly output of 10 ng of formic acid per cell, or about 5% of cell volume. Replenishing empty glands to their full formic acid load takes the beetle an estimated 37 days. Replenishing the 0.7 mg of formic acid expended in a single discharge takes 5.5 days.The noted British naturalist John Wray, in what must be one of the earliest references to insect chemistry (1), called attention to the production of an acid ''juyce'' by ants. Such fluid, containing formic acid, is well known nowadays to be ejected by ants of the subfamily Formicinae. Formic acid is a potent irritant, deterrent to vertebrates and invertebrates alike, and it serves ants effectively in defense (2). Not surprisingly, the capacity to produce the compound has evolved in other insects as well, notably in carabid beetles (3). We report here on one carabid, Galerita lecontei, that ejects a spray containing formic acid at the concentration of 80%. We describe the glands that produce the fluid, give details of the chemical composition of the liquid, and as part of an attempt to obtain some measure of the defensive ''budget'' of the beetle, provide an estimate of the rate at which formic acid is produced by the secretory cells of the glands.The study was prompted by preliminary observations by one of us (T.E.) on both G. lecontei and its morphologically very similar congener Galerita janus. Both beetles appeared to discharge formic acid, because they invariably came to reek characteristically of the compound when picked up by hand in the field. It was also clear that both beetles ejected the acid at high concentration, because the discharged fluid failed to turn filter paper impregnated with cobaltous chloride from blue to pink, indicating that it was relatively water-free. The data presented here were obtained almost exclusively with G. lecontei. Where obtained also with G. janus, it is so indicated. MATERIALS AND METHODSStatistics.Values are presented throughout as mean Ϯ SD. The Beetles. G. lecontei were taken in ultraviolet light traps in spring, on the grounds of the Archbold Biological Station, near Lake Placid, Highlands County, FL. The few G. janus that were also used were collected under rocks near streams in Ithaca, Tompkins County, NY. The beetles were kept in groups in containers with soil, and maintained for weeks on freshly cut up mealworms (larvae of Tenebrio molitor) and water. Body mass of G. lecontei m...

Absence asymmetry: The evolution of monorchid beetles (Insecta: Coleoptera: Carabidae)

“…Their evolution and maintenance is tightly tied to predation avoidance, and this defense is probably one of the major contributing factors to the success of Carabidae (Erwin, 1985;Will et al, 2000). The spray emitted by a beetle in response to predation is directional and unilateral (Rossini et al, 1997). Therefore, the glands are nonredundant: each works to protect its respective side.…”

Spray aiming in the bombardier beetle: Photographic evidence

“…Not surprisingly, many carabids have the capacity to aim their spray in different directions (5)(6)(7)(8)(9). None are perhaps better marksmen than the so-called bombardier beetles, as we document here photographically for one species, the African Stenaptinus insignis.…”

“…Diverse toxicants are produced by these glands, often at high concentrations, including acids, aldehydes, phenols, and quinones (2,3). Most carabids are able to eject these fluids forcibly, in the form of sprays (5)(6)(7)(8)(9).…”

“…Living at soil level, carabids are in constant danger from ants, against which they are protected by their dischargeable defensive glands (1)(2)(3). Paired devices, these glands take the form of more or less capacious sacs, lying side by side in the abdomen and opening on the abdominal tip (4,5). Diverse toxicants are produced by these glands, often at high concentrations, including acids, aldehydes, phenols, and quinones (2,3).…”

Age-related changes in the chemical composition of female pheromone gland of the Egyptian cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae)

“…The aldehyde (E)-2-decenal was identified as adefensive compound of the staphylinid Omaliinae and Proteininae (Dettner and Reissenweber, 1991 ), meanwhile nonane, decane and octane were detected from the carabid beetle Galerita lecontei abdominal defensive glands (Rossini et al, 1997). Bartelt et al (1993) found that males of the coleopteran Carpophilus antiquus emit E-E-E-E-6-8-diethyl-4-methyl-3-5-7-9-dodecatetraene as aggregation pheromone, (Z)-3-decen-1-ol was recognized from male long-horned cerambycid beetle Rosalia funebris (Ray et al, 2009) and 6-10-13-trimethyl-tetradecan-1-ol was confirmed from the stink bug, Stiretrus anchorago (Kochansky et al, 1989) as well.…”