Tree Crickets Research Articles

Preferred males are not always good providers: female choice and male investment in tree crickets

Female tree crickets (Oecanthus nigricornis) prefer large males but do not receive larger glandular courtship gifts from these males. This finding is puzzling from both the male and female perspectives, because females should prefer males providing more direct benefits, and because males who provide larger gifts achieve higher insemination success. We tested for differences in the quality of male secretions and found that larger males provided more proteinaceous food gifts than did rivals, which could explain why they are preferred by females. The preference in turn could cause depletion of food gift reserves in favored males, because natural remating rates are high and because even a single feeding bout negatively affects glandular stores. Most intriguingly, we showed that preferred males can adaptively decrease the size of courtship food-gifts provided (in order to conserve gifts for future mating events) when they perceive that the probability of multiple future mating opportunities is high. Thus, the elevated mating rates of preferred males (both before and after a focal mating event) could account for the small size of their courtship food-gifts. Key words: courtship-feeding, direct benefits, Gryllidae, mate choice, multiple mating, operational sex ratio. [Behav Ecol]

Precopulatory choice for cues of material benefits in tree crickets

The relative importance of direct and indirect benefits models of mate choice is a central question in sexual selection, but separating the two models is very difficult because high quality males often provide both better direct benefits and better genes. In tree crickets, Oecanthus nigricornis, females have the opportunity to gain both directly and indirectly from mate choice. Female tree crickets exercise premating choice for large males, but the model underlying this choice is unknown. In this study we examine the proximate cues used by female tree crickets to reject males, and show that the ability of males to provide food is a central cue. In contrast, we find no evidence that the relative size of mates is important in mate rejection. The fact that the major phenotypic cues of male quality are related to food provisioning suggests that the role of genetic benefits in shaping female preferences is limited by the extent to which food provisioning signals genetic quality.

Orthoptera in rice fields of Coimbatore

Orthopteran fauna in rice ecosystem at Coimbatore were surveyed in the Paddy Breeding Station and Wetlands of Tamil Nadu Agricultural University since 1997. Fifty species of Orthoptera (8 long-homed grasshoppers, 28 short-horned grasshoppers, 3 crickets, 1 tree cricket and 10 pygmy grasshoppers) were recorded in the survey. Those collected from the rice fields were found feeding on rice foliage and grains and a few of the Orthopterans viz., Anaxipha longipennis (Serv.), Metioche vittaticollis (Stal), Metioche bicolor (Stal.) (Trigonidiidae) collected mainly from the bunds were observed to be predators of rice insect pests.

Female Choice and the Consistency of Courtship Feeding in Black‐horned Tree Crickets Oecanthus nigricornis Walker (Orthoptera: Gryllidae: Oecanthinae)

Courtship feeding in insects is often strongly correlated with insemination duration and therefore provides a potential postcopulatory episode of sexual selection. We tested whether courtship feeding and other courtship traits in the black‐horned tree cricket Oecanthus nigricornis showed sufficient consistency potentially to respond to sexual selection by testing whether they differed significantly among males. Duration of courtship feeding differed among males when measured repeatedly and this caused significant differences in the duration of spermatophore attachment, a trait that determines the maximum duration of insemination and thus has important fitness consequences in crickets. We also partitioned variance in courtship behaviour between the sexes to test whether differences in courtship behaviour were attributable primarily to males, females or both sexes. Duration of spermatophore attachment was controlled by females and therefore represents a mechanism of female mate choice. Significant variation in duration of spermatophore attachment was associated with differences between individuals of both sexes. Differences among males indicate that females agree in their preference of certain males whereas differences among females indicate that females differ in their receptivity to postcopulatory courtship and insemination. The fact that differences among males in duration of spermatophore attachment were due to significant differences solely in the period of courtship feeding indicates that postcopulatory female choice was mediated through courtship feeding. Whether males manipulate female choices by allocating more or fewer resources requires further testing, but we found that males court some females more vigorously than others after females dismount. The number of previous mates had opposite effects on the duration of courtship feeding for the sexes, decreasing it for males but increasing it for females, and we discuss the possible causes of these results.

Mate choice in tree crickets and their kin.

Mate choice theory has become a major field of research in behavioral ecology. Tree crickets provide excellent opportunities for studying the diversity and variability of mate choice. The evidence for female mate choice in tree crickets is reviewed, and broad comparisons with other orthopteran groups are made. The evidence shows that female choice may occur during several different stages of mating and may target several different criteria. Song preferences are perhaps dominated by stabilizing preferences for the cues of species recognition, but there is a growing body of evidence for directional preferences based on sensory biases or mate quality. Mate rejection during courtship and forms of postcopulatory choice may favor males, based both on phenotypic quality and on the amount of nutritious courtship gifts they provide, and may differ with the value of mating incentives. Understanding the balance and trade-offs between different forms of mate choice may help in understanding their evolutionary causes.

Synchrony in cricket calling songs: Models of coupled biological oscillators

Snowy tree crickets produce a rhythmic acoustic signal composed of short chirps. The chirp rhythms are very regular and dependent on temperature. When signaling in groups, males synchronize their chirps. The rhythmic signals of these tree crickets were used as a model of a ‘‘biological oscillator.’’ The phase responses of males to single probe stimuli similar to the male calling song were measured. The phase response curves (PRC) of males showed both strong (type 0) and weak (type 1) resetting. PRCs differed depending on amplitude, duration, and frequency of the resetting stimuli. In other experiments, males could adjust their natural periods by as much as 15% when phase-locking (1:1) to an entrainment stimulus. Signaling behavior of males was compared with a simple model of coupled oscillators. The phase resetting was not consistent with the simplest resetting model, in which the male’s phase shift is completed after one cycle of the chirp period. In addition, a simple iteration of the PRC could not simulate the phase-locking observed in the entrainment experiments indicating that the acoustic coupling between males differs from a simple resetting model.

Courtship feeding in tree crickets increases insemination and female reproductive life span

Courtship feeding in the majority of insects may influence female reproductive patterns either directly, through effects of the gift material, or indirectly, through correlated effects of prolonged copulation and larger ejaculates. This distinction is important because the cause of changes in fecundity may influence patterns of the allocation of resources between the sexes, with implications for the intensity of sexual selection and magnitude of sexual conflict. I show that post-copulatory feeding on the secretions of a gland on the metanotum of maleOecanthus nigricornis. Walker correlates with oviposition and affects the number of sperm remaining within the spermatophore. Manipulations of gland feeding and insemination duration showed that changes in fecundity are due to the gift rather than the ejaculate. Metanotal gland feeding increased female fecundity by increasing reproductive life span without significantly increasing oviposition rate. These changes in reproduction were directly due to the gift itself. Although gland feeding was positively correlated with the duration of insemination and thus the number of sperm transferred from the spermatophore to the female, experimentally prolonging or reducing insemination had no significant effect on reproductive life span. Male phenotype was also associated with female fecundity but in this case the effect was caused by an increase in the oviposition rate of females that mated with relatively large males. Male size had no significant effect on female reproductive life span, suggesting that its effect is not simply due to a quantitative increase in gift size. Three other measures of male phenotype, fluctuating asymmetry, condition (i.e. size-standardized wet body mass) and age, had no significant effects on female reproduction.

Female remating and the intensity of female choice in black-horned tree crickets, Oecanthus nigricornis

Repeated mating by females of many species occurs at frequencies in excess of those needed to acquire additional sperm for fertilizing ova. I tested three alternative hypotheses for the rate of remating by females of the courtship-feeding tree cricket, Oecanthus nigricornis Walker, by manipulating diet quality and courtship feeding and measuring the time to remating by the female in relation to four aspects of male phenotype (age, condition, fluctuating asymmetry, and size). First, in courtship-feeding species, remating may be due to selection to increase the amount of nutritional resources provided by males, with nutrient-deprived females remating more quickly. Second, remating may function as a mechanism of postcopulatory mate choice, with females remating quickly when the quality of a previous mate is low. Third, quickness of remating may be the consequence of precopulatory mate choice prior to future matings, with females remating more quickly with high-quality males, regardless of the quality of prior mates. Females on a low-quality diet remated quickly, did not vary remating speed with the phenotype of their first mate, and did not differentially reject prospective second mates with different phenotypes. In contrast, both the degree of coyness (measured as the frequency of mate rejection) and the intensity of female choice (measured as the size differential between accepted and rejected mates) increased with diet quality. These results support both the material-benefits and the precopulatory mate-choice hypotheses for remating speed of female tree crickets. There was mixed support for the postcopulatory choice hypothesis: females on the high-quality diet remated more slowly after first mating with relatively large males, in support of the postcopulatory choice hypothesis; however, the remating interval of females on the high-quality diet decreased with the condition of the first mate, opposite to the prediction of the postcopulatory choice hypothesis

Reproductive biology and function of multiple mating in the mating system of a tree cricket,Truljalia hibinonis (Orthoptera: Podoscritinae)

A tree cricket,Truljalia hibinonis, is known to show a novel sperm removal during copulation. The pattern of copulations and ovipositions showed that the sperm removal functioned to increase reproductive success for sperm removing males. The sperm removal by males evolves under the system in which female accept multiple mating. The possible benefits of multiple mating for females are examined. Multiple mating did not seem to be necessary for avoiding sperm depletion, because females stored huge number of sperm in their sperm storage organ after finishing oviposition. The ingestion of metanotal secretion during copulation also had no effect on increasing fecundity and egg size. However, mating experience may have a positive effect on increasing fecundity slightly, though there were no differences between once- and twice-mated females. The other possible benefits for each male and female are discussed.

A New Japanese Species of Leptoteleia KIEFFER (Hymenoptera, Scelionidae), Reared from Eggs of the Green Tree Cricket :

A New Japanese Species of Leptoteleia KIEFFER (Hymenoptera, Scelionidae), Reared from Eggs of the Green Tree Cricket :

Natural Enemies and Plant Water Relations Influence the Distribution of an Armored Scale Insect

In urban settings, the armored scale insect Pseudaulacaspis pentagona infests mulberry trees in disturbed landscape habitats (roadsides, parking lots) but not trees in forested habitats (woodlots). Populations of P. pentagona are contagiously distributed among mulberry trees in landscape habitats. We investigated how two factors, natural enemies and plant water potential, interact to affect the spatial distribution and abundance of P. pentagona. Survivorship of P. pentagona (caged with enemies excluded) was significantly lower on scale—free landscape trees than on scale—infested landscape trees or forest trees. Differences in scale survivorship disappeared, however, when scales were raised on greenhouse—grown clones of these same field trees, suggesting that variation in survivorship was due to the habitat in which trees grew. The survivorship of caged scales (enemies excluded) on field trees was positively related to midday water potential, an index of plant moisture stress. Scale—free landscape trees had significantly lower midday water potentials than did either scale—infested landscape trees or forest trees. Patterns of water potential and scale survivorship across trees suggested that the absence of P. pentagona on landscape trees with a history of scale absence was attributable to plant water relations. Moreover, highly significant differences in water potential occurred between infested and scale—free mulberry trees located <10 m apart, suggesting that moisture deficit influences the performance and abundance of scale insects over small distances. When cohorts of P. pentagona were raised on field trees and exposed to natural enemies for one generation, mortality was significantly higher on forest trees than on either scale—free or scale—infested landscape trees. High scale mortality in the forest habitat was attributable to abundant generalist predators. (e.g., phalangids, earwigs, and tree crickets). Scale mortality in the landscape habitat, due to specialized coccinellid predators and aphenlinid parasitoids, was much lower than in the forest habitat. The patchy distribution of P. pentagona in Maryland is best explained by the combined influences of natural enemies and plant water relations. P. pentagona infests a small subset of mulberry trees in the urban landscape that are without water deficits and free of generalist invertebrate predators.

Incidental effects and evolution of sound-producing organs in tree crickets (Orthoptera : Oecanthidae)

Male tree cricket (Orthoptera : Oecanthidae) calling songs are used by females to locate conspecific mates. Changes in these songs are crucial to speciation. Since certain features of cricket sounds are correlated with the structures of the stridulatory organs, changes in stridulatory organs must be correlated with changes in songs. Surprisingly, there is no established hypothesis to explain the mechanism of morphological change associated with changes in songs. Some alternative possibilities are explored, with reference to incidental effects. Available evidence suggests that stridulatory organs are genetically stable and that changes in these organs occur in steps rather than gradually.

Ultrasubharmonic resonance and nonlinear dynamics in the song of Oecanthus nigricornis F. Walker (Orthoptera : Gryllidae)

In the few cricket species that have been studied, there is a 1 : 1 relationship between carrier frequency and tooth-strike rate in normal song. However, for the vast majority of cricket species that relationship remains unknown. In the tree cricket, Oecanthus nigricornis F. Walker (Orthoptera : Gryllidae : Oecanthinae), the carrier frequency of the song normally equals the tooth-strike rate; rarely, the two are different and phase-locked in ultrasubharmonic ratios, such as 4 : 3 or 5 : 4. Sometimes, both frequencies are simultaneously present, giving rise to acoustic beats with 2 sharp frequency peaks related by similar ratios. The above phenomena were artificially induced in normal live singing crickets by experimental modification of one or both tegmina: beats arise when one of the tegmina vibrates at the tooth-strike frequency, while the other vibrates at the ultrasubharmonic frequency. A mathematical model is presented of the Oecanthus tegminal resonator, consisting of 2 simple coupled differential equations, one of them with a nonlinear restoring term. Integration of the model at various values of tooth-strike rate and exciting force, yields all of the observed phenomena, including normal and ultrasubharmonic output frequencies as well as beats between them. The resulting waveforms and acoustic spectra accurately reproduce those found in natural and experimental recordings.

Effects of temperature on chirp rates of tree crickets (Orthoptera: Oecanthidae)

The relationship between temperature and chirp rate is described for three African tree crickets, Oecanthus capensis, O. karschi and O. sycomorus. Knowledge of the variation in the chirp rates of O. karschi and O. capensis makes it possible to discriminate between the songs of these species with a stopwatch. Their songs can also be used to estimate air temperature. When signals like cricket songs change with temperature, the response may also be affected. Some problems associated with temperature dependent communication systems are discussed.

Power output and efficiency of sound production by crickets

Male crickets produce calling songs that function to attract mates. Sound is produced when membranes of the wings are caused to vibrate during stridulation. Sound fields were measured for three species of crickets. Two species of mole crickets, Scapteriscus acletus and s. vicinus, call from within burrows constructed in the soil. Sound fields of the mole crickets were hemispherical and the power output averaged 4 μW (N = 22, range 2–22 μW). Power output was dependent upon male size and moisture content of soil surrounding the burrow. Efficiency of sound production was estimated to be less than 0.2%. Sound fields of a species of tree crickets, Oecanthus quadripunctatus, approximated that of a doublet source. Power output ranged from 2–17 μW (N = 6) and efficiency was estimated at about 1%.

Removal and subsequent ingestion of rivals' semen during copulation in a tree cricket

ABSTRACT. A novel combination of adaptations resulting from sperm competition is demonstrated for the tree cricket Truljalia hibinonis (Matsumura) (Podoscirtinae: Gryllidae: Orthoptera). 87.5% of the semen of previous males is displaced onto the penis of the copulating male and is removed at the end of copulation. Semen thus removed is ingested during post‐copulatory oro‐genital grooming. No overt morphological adaptations for sperm removal were observed and, on the basis of anatomical evidence, it is suggested that rivals' semen is flushed out of the female?s sperm storage organ by the semen of the last male.

Power output and efficiency of sound production by crickets

Male crickets produce calling songs that function to attract mates. Sound is produced when membranes of the wings are caused to vibrate during stridulation. Sound fields were measured for three species of crickets. Two species of mole crickets, Scapteriscus acletus and s. vicinus, call from within burrows constructed in the soil. Sound fields of the mole crickets were hemispherical and the power output averaged 4 μW (N = 22, range 2–22 μW). Power output was dependent upon male size and moisture content of soil surrounding the burrow. Efficiency of sound production was estimated to be less than 0.2%. Sound fields of a species of tree crickets, Oecanthus quadripunctatus, approximated that of a doublet source. Power output ranged from 2–17 μW (N = 6) and efficiency was estimated at about 1%.

Diet of Leadbeaters Possum, Gymnobelideus Leadbeateri (Marsupialia).

Diet of Leadbeater's possum (Gymnobelideus leadbeateri) in Victoria, Australia, in a forest dominated by Eucalyptus regnans was found by examination of faeces and limited direct observation. It included arthropods, particularly tree crickets, beetles, moths, and spiders, plant exudates such as Acacia gum, nectar and manna, and the insect exudate psyllid honeydew. Arthropods were calculated to provide less than 20% of daily energy requirements. The overall pattern of ingestion was similar to that previously reported for the related sugar glider, but seasonal shortage of exudates was more pronounced during winter.

Diet of the Yellow-bellied Glider Petaurus australis (Marsupialia: Petauridae) in north Queensland.

The diet of the Yellow-bellied Glider was studied at Herberton in north Queensland by faecal analysis. The Glider was found to consume a variety of arboreal arthropods, principally tree crickets, adult and larval beetles, caterpillars and spiders. The bulk of the diet was thought to consist of exudates including eucalypt sap, eucalypt nectar and to a lesser extent insect honey dew. Some aspects of the life history of this species are consistent with a high sap, low arthropod (and hence protein) diet.

Energetics of singing in crickets: Effect of temperature in three trilling species (Orthoptera: Gryllidae)

1. Oxygen consumptions of resting and trilling crickets were measured at various temperatures. Oscillograms taken at comparable temperatures were used to identify the major factors determining the cost of stridulation. 2. Species used wereAnurogryllus arboreus (mass ≃0.4 g), wing stroke rate at 23°C of 71 strokes per s; andOecanthus celerinictus andO. quadripunctatus, two sibling species, (masses ≃0.06 g), wing stroke rates at 23°C of 57 and 38 strokes per s respectively. 3. At 23°C the three species have similar total mass-specific metabolism during singing (\(\dot V_{O_2 }\) μl·(g·h)−1; Table 3) even though their wing stroke rates are different. 4. A. arboreus has no change in net singing metabolism with increasingTa; however, cost per wing stroke decreases slightly. TheOecanthus both increase their net singing costs with increasedTa and the cost per wing stroke remains roughly constant.O. quadripunctatus has a cost per wing stroke about 1.6 timesO. celerinictus (Tables 1, 3; Fig. 10).A. arboreus does not elevate its thoracic temperature significantly while stridulating and it is doubtful that tree crickets thermoregulate due to their small size. 5. The cost of singing inA. arboreus varies from 10 to 16 times resting; inOecanthus, from 6 to 12 times resting (Table 3). 6. Although the two tree cricket species have different wing stroke rates at any common temperature, the number of file teeth struck per s is almost the same;A. arboreus strikes nearly twice as many teeth per s as do either of the tree crickets (Fig. 9). 7. The two factors that explain most of the variation in net cost of trilling are the wing stroke rate (Fig. 10) and the number of teeth struck·(wing stroke)−1. Related factors that merit study are interspecific differences in file tooth depth and angle, wing mass, and wing velocity. 8. For three species of crickets and two species of katydids the average net cost of trilling is about 1.5×10−5 ml O2·(g·wing stroke)−1 (Fig. 10). 9. Chirping should be energetically less expensive than trilling, with costs equivalent to the average cost per wing stroke times the total number of wing strokes per time. The latter factor is 10–95% lower in chirping species than in trillers. 10. An estimated daily respiratory energy budget shows calling taking about 56% of the daily respiratory budget ofO. celerinictus and 26% forA. arboreus (Table 4).