Chemical defense: aquatic beetle (Dineutes hornii) vs. fish (Micropterus salmoides).

Captive largemouth bass (Micropterus salmoides) reject the gyrinid beetle, Dineutes hornii. They also reject edible items (mealworms) treated by topical addition of the norsesquiterpene gyrinidal, the principal component of the defensive secretion of the beetle. The bass' oral tolerance of gyrinidal varies broadly as a function of the gyrinidal dosage and the state of satiation of the fish. When taking a D. hornii or a gyrinidal-treated mealworm in the mouth, the fish subjects the item to an intensive oral flushing behavior, seemingly intended to rid the item of gyrinidal. The duration of oral flushing is itself a function of the gyrinidal dosage and the state of satiation of the bass. To counter oral flushing, D. hornii emits its secretion as a slow trickle. Duration of emission is slightly longer (1.5 min) than the time (1.3 min) invested by the bass in flushing a D. hornii before rejecting the beetle. We postulate that flush resistance may be a general feature of defensive chemical delivery systems in aquatic prey, given that oral flushing may be a common strategy of fish.

Voltage clamping single cells in intact malpighian tubules of mosquitoes.

Principal cells of the Malpighian tubule of the yellow fever mosquito were studied with the methods of two-electrode voltage clamp (TEVC). Intracellular voltage (V(pc)) was -86.7 mV, and input resistance (R(pc)) was 388.5 kOmega (n = 49 cells). In six cells, Ba(2+) (15 mM) had negligible effects on V(pc), but it increased R(pc) from 325.3 to 684.5 kOmega (P < 0.001). In the presence of Ba(2+), leucokinin-VIII (1 microM) increased V(pc) to -101.8 mV (P < 0.001) and reduced R(pc) to 340.2 kOmega (P < 0.002). Circuit analysis yields the following: basolateral membrane resistance, 652. 0 kOmega; apical membrane resistance, 340.2 kOmega; shunt resistance (R(sh)), 344.3 kOmega; transcellular resistance, 992.2 kOmega. The fractional resistance of the apical membrane (0.35) and the ratio of transcellular resistance and R(sh) (3.53) agree closely with values obtained by cable analysis in isolated perfused tubules and confirm the usefulness of TEVC methods in single principal cells of the intact Malpighian tubule. Dinitrophenol (0.1 mM) reversibly depolarized V(pc) from -94.3 to -10.7 mV (P < 0.001) and reversibly increased R(pc) from 412 to 2,879 kOmega (P < 0.001), effects that were duplicated by cyanide (0.3 mM). Significant effects of metabolic inhibition on voltage and resistance suggest a role of ATP in electrogenesis and the maintenance of conductive transport pathways.

Defense by foot adhesion in a beetle (Hemisphaerota cyanea).

The beetle Hemisphaerota cyanea (Chrysomelidae; Cassidinae) responds to disturbance by activating a tarsal adhesion mechanism by which it secures a hold on the substrate. Its tarsi are oversized and collectively bear some 60,000 adhesive bristles, each with two terminal pads. While walking, the beetle commits but a small fraction of the bristles to contact with the substrate. But when assaulted, it presses its tarsi flatly down, thereby touching ground with all or nearly all of the bristles. Once so adhered, it can withstand pulling forces of up to 0.8 g ( approximately 60 times its body mass) for 2 min, and of higher magnitudes, up to >3 g, for shorter periods. Adhesion is secured by a liquid, most probably an oil. By adhering, the beetle is able to thwart attacking ants, given that it is able to cling more persistently than the ant persists in its assault. One predator, the reduviid Arilus cristatus, is able to feed on the beetle, possibly because by injecting venom it prevents the beetle from maintaining its tarsal hold.

Spray mechanism of the most primitive bombardier beetle (Metrius contractus).

The bombardier beetle Metrius contractus discharges its defensive secretion as a froth that clings to its body. When attacked from the rear, it allows the froth to build up over the gland openings near the abdominal tip; when attacked from the front, it conveys the secretion forwards along special elytral tracks. M. contractus has two-chambered defensive glands typical of bombardier beetles, and its secretion, like that of other bombardiers, is quinonoid and hot. Its frothing mechanism, however, is unique for bombardiers and possibly illustrative of the ancestral glandular discharge mechanism of these beetles. M. contractus, thus, could be the least derived of extant bombardiers.

Oscillations of voltage and resistance in Malpighian tubules of Aedes aegypti.

The transepithelial voltage (V(t)) of isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti spontaneously oscillates in more than half the tubules. Typically, V(t) decreases and then rises at a frequency of 2 oscillations/min with a duration of 16 s. In 6 isolated perfused tubules studied in detail, V(t) oscillates between 50.5 mV and 15.7 mV in parallel with (1) oscillations of the transepithelial resistance (R(t)) between 7.61 kOmegacm and 3.63 kOmegacm, (2) oscillations of the basolateral membrane voltage of principal cells between -56.7 mV and -72.2 mV, and (3) oscillations of the apical membrane voltage between 107.2 mV and 87.8 mV. The oscillations are dependent on the Cl concentration in the extracellular solutions. As R(t) decreases during the oscillations V(t) goes to the transepithelial equilibrium potential of Cl (E(cl)) indicating transient changes in transepithelial Cl conductance as the mechanism of voltage and resistance oscillations. Since the largest voltage oscillations take place across the whole epithelium and not across cell membranes, oscillating Cl conductances are localized to a single transepithelial Cl diffusion barrier such as the paracellular pathway. This conclusion is supported by the analysis of electrically equivalent circuits that identify the shunt pathway as the site of oscillating Cl conductances.

Spray aiming in the bombardier beetle: photographic evidence.

Bombardier beetles, when physically assaulted, eject a hot quinonoid spray from the tip of the abdomen. Photographic evidence is presented demonstrating that the African bombardier beetle, Stenaptinus insignis, can aim its spray in virtually any direction. It can target its individual legs, and even the individual segments of its legs. Moreover, in aiming at a leg, it takes into account the postural orientation of that leg. The beetle is able even to target sites on its back. It is postulated that the ability to aim helps the beetle mainly in defense against ants.

Fractal-based image texture analysis of trabecular bone architecture.

Fractal-based image analysis methods are investigated to extract textural features related to the anisotropic structure of trabecular bone from the X-ray images of cubic bone specimens. Three methods are used to quantify image textural features: power spectrum, Minkowski dimension and mean intercept length. The global fractal dimension is used to describe the overall roughness of the image texture. The anisotropic features formed by the trabeculae are characterised by a fabric ellipse, whose orientation and eccentricity reflect the textural anisotropy of the image. Tests of these methods with synthetic images of known fractal dimension show that the Minkowski dimension provides a more accurate and consistent estimation of global fractal dimension. Tests on bone x-ray (eccentricity range 0.25-0.80) images indicate that the Minkowski dimension is more sensitive to the changes in textural orientation. The results suggest that the Minkowski dimension is a better measure for characterising trabecular bone anisotropy in the x-ray images of thick specimens.

Responses of the bovine mammary artery to angiotensins.

The main objective of our study was to determine whether angiotensins cause vasoconstriction of mammary arterial segments in vitro. Once this action was established, its specificity was determined. Mammary arterial sections were obtained from lactating cattle at slaughter. Vessel sections were placed in a gravity-fed, closed, perfusion apparatus, and flow was measured by a transit-time flow sensor mounted in-line. Treatments were administered by injection into a leurlock port located proximal to the sensor. Angiotensins I, II, and III induced a dose-dependent vasoconstriction of arterial segments at concentrations of 5 x 10(-10) to 5 x 10(-6) M. Angiotensin II receptor antagonists, Saralisin and (Sarl, Thr8)-angiotensin II (5 x 10(-8) M)), inhibited vasoconstriction induced by angiotensins I, II, and III. The angiotensin-converting enzyme inhibitor, Captopril (5 x 10(-8) M), inhibited angiotensin I vasoconstriction, thereby showing that the vasoconstriction by angiotensin I was mediated through its conversion to angiotensin II. These data demonstrated that the mammary artery of lactating cows is responsive to the angiotensin family. Furthermore, mammary arteries contain angiotensin-converting enzyme and specific receptors for angiotensin II. This system may be important in the normal physiological regulation of mammary gland blood flow of lactating cows.

Effects of voltages on cows over a complete lactation. 1. Milk yield and composition.

The effect of long-term voltage exposure on milk yield and composition was assessed. Forty cows in second to fifth lactation were used. Four groups of 10 Holstein cows were exposed to either 0, 1, 2, or 4 V throughout an entire lactation. Each group was housed in a free-stall environment with bunk feed and water provided for ad libitum intake. Voltages (AC, 60 Hz) were applied between waterers and a metal grid. Cows could not drink without placing their front hooves on the metal grid. Individual records were maintained for milk weights, milk fat, protein, and somatic cell counts. Average actual (7312, 8527, 6938, and 7725 kg for groups exposed to 0, 1, 2, or 4 V, respectively) and mature equivalent (7802, 9281, 7308, and 8911 kg for groups exposed to 0, 1, 2, or 4 V, respectively) milk weights for 305 d showed no significant differences between groups exposed or unexposed to voltage. Average actual milk yields for 305 d in the previous lactations were 8016, 8163, 7679, and 7876 kg for groups exposed to 0, 1, 2, or 4 V, respectively. Somatic cell counts, milk fat, and protein showed no significant differences between groups exposed or unexposed to voltage. Feed and water intakes were not affected by voltage.

Effects of voltages on cows over a complete lactation. 2. Health and reproduction.

For the effects of voltages on health and reproduction, 40 cows in second to fifth lactation were divided into four groups of 10. These included a control group that was not subjected to voltages and three treatment groups that were given either 1, 2, or 4 V at the water bowl. Cows in the treatment groups were exposed during the entire lactation to voltage whenever they drank. Voltages did not sufficiently affect milk yield. General health parameters studied were mastitis, hoof problems, and changes in body weight. Reproductive and calving parameters examined were days to first breeding, days open, services per conception, response to PGF2 alpha, calving intervals, visible abortion, and calves born dead. Voltages did not significantly influence cow health or reproductive performance.

Cow sensitivity to electricity during milking.

Alternating currents were delivered to lactating cattle through the milk during milking. Electrodes were placed at the top of each short milk tube and jointed for one electrical contact. A metal grid on which the cows' rear hooves stood during milking was the second contact. Constant voltages (0 to 16 V) applied to contacts showed first lactation cows to be more sensitive than multiple lactation cows. First lactation cows kicked milking machines at 8 V (currents greater than 5 mA), and multiple lactation cows kicked at 16 V (currents greater than 8 mA). At lower voltages, there were no consistent significant differences in milking duration, milk yield, or composition for primary or residual milk. Application of constant currents of 5 mA for first lactation cows and 8 mA for multiple lactation cows produced no undesired behaviors but did result in some differences in production variables. Milking duration decreased during application of constant current to first lactation cows. Blood cortisol monitored in the multiple lactation cows during trial 2 showed a significant increase during milking but was equivalent or less during application of current. This study demonstrates that currents of 5 mA or less, delivered through the milk line, did not produce any direct economic effect. To produce this current, voltages on the milk pipe line would have to be in excess of 125 V (obvious human safety hazard) or in excess of 5 V on the claw of the milking cluster.

Unique electrophysiological effects of dinitrophenol in Malpighian tubules.

In the course of electrophysiological studies of Malpighian tubules of the mosquito Aedes aegypti, we have found unusual effects of 2,4-dinitrophenol (DNP) that offer new insights into the electrogenic and conductive properties of the tubule. DNP (10(-4)M) depolarized the basolateral membrane voltage from -58.0 to -3.3 mV, and it depolarized the apical membrane voltage from 110.6 to 8.9 mV. In parallel the transepithelial electrical resistance increased from 11.4 to 16.8 k omega.cm, and the fractional resistance of the apical membrane increased from 0.32 to 0.57. On the assumption that measures of transepithelial resistance in the presence of DNP approach the shunt resistance, the experimental results indicate the following characteristics for the equivalent circuit of the tubule: 1) a shunt resistance that is approximately one-half the transcellular resistance, 2) low and high electromotive forces, respectively, at the basolateral and apical membranes of principal cells, 3) an electrogenic pump at the apical membrane, and 4) a basolateral membrane voltage that is due mostly to the voltage developed by current flow across the basolateral membrane resistance.

Parentally provided alkaloid does not protect eggs ofUtetheisa ornatrix (Lepidoptera: Arctiidae) against entomopathogenic fungi.

Eggs ofUtetheisa ornatrix proved equally vulnerable to fungal infection (Beauveria bassiana, Paecilomyces lilacinus) whether they contained parentally provided pyrrolizidine alkaloid (monocrotaline) or were free of such alkaloid. In in vitro tests, monocrotaline, either as free base or N-oxide, had no inhibiting effect on fungal cultures.

Defensive spray of the bombardier beetle: a biological pulse jet.

The defensive spray of the bombardier beetle Stenaptinus insignis is ejected in quick pulses (at about 500 pulses per second) rather than as a continuous stream. The pulsation may be a consequence of intermittency in the explosive chemical process that generates the spray. The ejection system of the beetle shows basic similarity to the pulse jet propulsion mechanism of the German V-1 "buzz" bomb of World War II.

Defensive alkaloid in blood of Mexican bean beetle (Epilachna varivestis).

The blood of the Mexican bean beetle (Epilachna varivestis) contains a homotropane alkaloid, euphococcinine (1). The beetles 'reflex bleed' when disturbed, thereby deploying the alkaloid, which is provenly deterrent to spiders and ants. Newly emerged adults lack the alkaloid, but the compound builds up to deterrent levels in their blood within days. Eggs and larvae of Epilachna are devoid of the compound.

Predatory capture of toads by fly larvae.

A natural occurrence of predation upon toads (Scaphiopus multiplicatus) by fly larvae (Tabanus punctifer) is described. The larvae lie buried in mud, seize the toads with hooked mandibles, pull them partly into the mud, and kill them by feeding on their body fluids. The larvae may ordinarily subsist mostly on invertebrates and take Amphibia only opportunistically.

Spray aiming in bombardier beetles: jet deflection by the coanda effect.

Bombardier beetles of the carabid subfamily Paussinae have a pair of flanges, diagnostic for the group, that project outward from the sides of the body. Behind each flange is a gland opening, from which the beetles discharge a hot, quinone-containing secretion when disturbed. The flanges are curved and grooved and serve as launching guides for anteriorly aimed ejections of secretion. Jets of fluid, on emergence from the gland openings, follow the curvature of the flanges and are thereby bent sharply in their trajectory and directed forward. The phenomenon is illustrative of the Coanda effect, widely applicable in engineering and responsible for the familiar tendency of liquids to curve around spouts and down the front of containers when being poured.

Ultraviolet patterns on rear of flowers: basis of disparity of buds and blossoms.

Flowers of Jasminium primulinum and Hypericum spp. have ultraviolet patterns on the reverse surface of the corolla. Those areas of the surface that are exposed to the outside in the bud are ultraviolet absorbent, whereas the portions that come into view at maturity in the open blossom are ultraviolet reflectant. Buds and blossoms, as a result, appear different in color to insects sensitive to ultraviolet light. Experimental evidence indicates that the ultraviolet-absorbent quality of the outer surface of the bud is a consequence of exposure itself, attributable possibly to a "sun tanning" effect.