Female Elytra Research Articles

Defining generic limits in Syndesini MacLeay, 1819 (Coleoptera: Lucanidae: Syndesinae) through taxonomy and geometric morphometrics

A comparative taxonomic study was performed between the Syndesini genera Syndesus MacLeay, 1819 and Psilodon Perty, 1830. Both taxa are redescribed, with the addition of more precise diagnostic traits, including the description of male and female genitalia. We provide comparative remarks to support the separation of both genera, with additional information obtained through the application of geometric morphometric analysis to the following morphological structures: right mandible of males (RMM); lateral view of left mandible of males (LMM); lateral view of males pronotal tubercle (PT); dorsal face of male and female pronotum (DFP); dorsal face of male and female elytra (DFE). The shapes of all analysed traits showed to be different through the performance of Principal Component Analyses producing two well-define clusters, except for the elytral shape which showed a high superposition, however all Procrustes and Mahalanobis distances showed significant differences, supporting the existence of two Syndesini genera instead of one. It was also possible to register a significant influence regarding the biogeographic distribution of the specimens, obtaining statistical differences when comparing the shape data from the Australasian and Neotropical biogeographic dominions, suggesting a strong relation between Syndesus and Psilodon divergence and the Gondwanan vicariant events. Finally, a checklist was provided including all the described species for both genera.

The taste of origin in a lady beetle: do males discriminate between females based on cuticular hydrocarbons?

AbstractThe Asian lady beetle Harmonia axyridis originates from Asia and has established invasive populations worldwide. Recent population genetic studies trace their invasion routes and demonstrate that bottlenecks in population size have reduced their genetic diversity. Consequently, phenotypical differences are highlighted between native and invasive populations. Among phenotypical traits, cuticular hydrocarbons (CHCs) might reflect the geographical origin of a lady beetle, especially because of their genetic basis. The present study investigates whether (i) the CHC profiles qualitatively and quantitatively differ between females of H. axyridis from native and invasive populations and (ii) males discriminate females from native and invasive populations using CHC profiles. CHCs are solvent‐extracted before being quantified and identified by gas chromatography and mass spectrometry. In total, 17 CHCs are detected from female elytra, including six alkanes, three polyunsaturated and eight monounsaturated alkenes. The total quantity of CHCs differs among the populations, with lady beetles from Tai'an (China) displaying higher CHC concentrations than lady beetles from Gembloux (Belgium) and from Beijing (China) populations. Multivariate analyses detect differences in CHC qualitative profiles, with females from Tai'an being different from the two other populations. Finally, behavioural assays show that females originating from the native Tai'an population are less preferred by males, whereas females from the invasive population are mounted more often. The behavioural assays suggest that CHCs are not involved in discrimination of mating partners based on their origin.

New results on sexual differences in tarsal adhesive setae of Diabrotica virgifera virgifera LeConte (Coleoptera, Chrysomelidae, Galerucinae)

Previous light microscopy studies revealed a hairless patch on the feet of male Diabrotica virgifera virgifera. However, in related species of chrysomelid beetles the males have special adhesive setae with discoid terminals, which adhere to the elytra of females during copulation. In the present study, we examined the pretarsi of D. virgifera virgifera at a high magnification using scanning electron microscopy. The distinct sexual tarsal dimorphism in this species is confirmed. However, our results do not support the presence of a hairless patch on the feet of males, but a field of densely-packed male-specific adhesive setae with discoid terminals.

Structural origin of sexual dichromatic coloration and luster in the beetle Goliathus cacicus

In the beetle Goliathus cacicus, male elytra show silky luster with iridescence while female ones appear lusterless white without iridescence to our perception. We revealed by structural characterizations and optical measurements that elytral coloration and luster of both male and female beetles stem from the tubular scales on the elytra, whose interior is filled with a random structure. Distinct differences between male and female scales reside in the cortex thickness and the filling fraction of the random structure, which are important factors in the determination of the sexual dichromatic luster and iridescence. In additional to reflection peaks in the visible range, spectral measurements indicate that both male and female elytra display also strong iridescent ultraviolet (UV) reflections. Scattering spectra show that both male and female elytra display UV luster, although it is absent for female ones in the visible range.

Beetle adhesive hairs differ in stiffness and stickiness: in vivo adhesion measurements on individual setae

Leaf beetles are able to climb on smooth and rough surfaces using arrays of micron-sized adhesive hairs (setae) of varying morphology. We report the first in vivo adhesive force measurements of individual setae in the beetle Gastrophysa viridula, using a smooth polystyrene substrate attached to a glass capillary micro-cantilever. The beetles possess three distinct adhesive pads on each leg which differ in function and setal morphology. Visualisation of pull-offs allowed forces to be measured for each tarsal hair type. Male discoidal hairs adhered with the highest forces (919 ± 104nN, mean ± SE), followed by spatulate (582 ± 59nN) and pointed (127 ± 19nN) hairs. Discoidal hairs were stiffer in the normal direction (0.693 ± 0.111N m(-1)) than spatulate (0.364 ± 0.039N m(-1)) or pointed (0.192 ± 0.044N m(-1)) hairs. The greater adhesion on smooth surfaces and the higher stability of discoidal hairs help male beetles to achieve strong adhesion on the elytra of females during copulation. A comparison of pull-off forces measured for single setae and whole pads (arrays) revealed comparable levels of adhesive stress. This suggests that beetles are able to achieve equal load sharing across their adhesive pads so that detachment through peeling is prevented.

Chemical communication in mate location and recognition in the white-spotted longicorn beetle, Anoplophora malasiaca (Coleoptera: Cerambycidae)

The mating sequence has been studied in the white-spotted longicorn beetle, Anoplophora malasiaca (Thomson) (Coleoptera: Cerambycidae). Both females and males are attracted to wounded host plant Citrus unshiu, and adults of both sexes, and both female and male elytra contained the sesquiterpenes that were identical with those in C. unshiu. Moreover, at close range orientation by males, some visual cues derived from females acted synergistically with olfactory factors. And, female contact sex pheromone was isolated from female elytra and revealed to consist of eight hydrocarbons, four ketones, and three lactones. The mating sequence of A. malasiaca was roughly considered to occur as follows. Emerged adults from trunks of the host plants must search for their mates over large areas. Highly mobile males may be attracted from long distances by the signal of sesquiterpenes released from wounded host plants which indicate the presence of other individuals and serve for intraspecific communication in A. malasiaca. At close range orientation, the sesquiterpenes also act as attractant for both females and males, and then visual cue guided them to their mates or rivals. After a male orients to another individual, he identifies it as a mate or a rival. Once a male recognizes a female, mating occurs.

Sexual Dimorphism of Basitarsi in Pest Species of <I>Diabrotica</I> and <I>Cerotoma</I> (Coleoptera: Chrysomelidae)

Sexual dimorphism in basitarsal pad morphology is described for prothoracic and mesothoracic legs of Diabrotica virgifera virgifera LeConte, Diabrotica barberi Smith & Lawrence, and Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae) and for prothoracic legs of Cerotoma trifurcata (Forster) (Coleoptera: Chrysomelidae). On the indicated legs of these diabroticite beetles, the typical structure of the hairy tarsal pads of chrysomelid beetles is replaced proximally on tarsomere 1 of males by a hairless planar ovoid patch that may facilitate maintenance of the mating posture of males upon the elytra of females. This basitarsal patch proved as reliable as the standard supra-anal plate character for establishing sex of these important crop pests.

Influence of Host Gender on Infection Rate, Density and Distribution of the Parasitic Fungus,Hesperomyces virescens,on the Multicolored Asian Lady Beetle,Harmonia axyridis

Hesperomyces virescens Thaxter (Laboulbeniales: Laboulbeniaceae) is a parasitic fungus that infects lady beetles (Coleoptera: Coccinellidae) via horizontal transmission between adults at overwintering and feeding sites. The differential behavior of male and female hosts could have profound effects on intensity of infection and positioning of fungus on the host's integument. The influence of host gender on infection rate, density and distribution of this parasite on the multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), was determined at a feeding site. Adult H. axyridis were sampled from pecan, Carya illinoinensis (Wangenh.) K. Koch, trees in northern Mississippi, USA, during summer and early fall 2003–2004. Results indicated that the behavior of male or female beetles on pecan trees had only a limited effect on the intensity of infection. When averaged over the entire season, the percentage of H. axyridis infected with H. virescens was not influenced by host gender. In 2003, a seasonal average of 54 and 39% of males and females, respectively, were infected; whereas in 2004, 36 and 41% of male and female beetles, respectively, were infected. The percentage of males infected with H. virescens was correlated with the number of males captured at the site in 2003; infection rate decreased as male abundance increased. Infection rate did not correlate with female abundance in 2003 or male or female abundance in 2004. Host gender had a considerable effect on the density and distribution of the fungus. Hesperomyces virescens mature thalli were denser on male rather than female beetles. Also, thallus density was often greatest on the elytra, meso- and metathorax, and abdomen of males and elytra of females, than on other body parts, in 2003. In 2003 and 2004, approximately 59 and 97% and 67 and 96% of males and females, respectively, had mature thalli distributed on the elytra. Prevalence of H. virescens thalli on the dorsum of H. axyridis females suggests that mating behavior is important in fungal transmission. However, prevalence of thalli on the dorsum of H. axyridis males suggests that behaviors other than mating contribute to the transmission of H. virescens onto male beetles. Spread of H. virescens ascospores from infected to uninfected H. axyridis adults of different generations, at feeding sites, might be vital to maintaining stable populations of the fungus.

No Apparent Indirect Genetic Benefits to Female Red Flour Beetles Preferring Males with Intense Copulatory Courtship

Whether females gain indirect genetic benefits through mate choice is a controversial issue since this requires additive genetic variance in the preferred male traits. Condition dependence could maintain the necessary genetic variance by linking the expression of male traits to the supposedly large number of genes affecting condition. Copulating males of the red flour beetle Tribolium castaneum rub their legs along the female elytra. Females favor males with vigorous rubbing through cryptic female choice. We measured the repeatability and heritability of this behavior and assessed its potential use as indicator of viability and condition. We found genetic variance in larval to adult survival and in the rate of leg rubbing in males. However, the rate of leg rubbing was not related to offspring survival or condition dependent. The genetic variance in leg rubbing was mostly non-additive with very low narrow sense heritability. Therefore, we failed to document any indirect genetic benefits to choosy females through viability of their offspring or attractiveness of their sons.

Sexing adults of the strawberry blossom weevil, Anthonomus rubi (Col., Curculionidae)

Of several previously reported methods for sexing the strawberry blossom weevil, the presence of thorns on the intermediary coxae of males is the most convenient and unambiguous. Uniform pitting on the dorsal elytra of females provides the possible selective pressure for male thorn development.