Parastizopus Armaticeps Research Articles

Immature Stages of Beetles Representing the ‘Opatrinoid’ Clade (Coleoptera: Tenebrionidae): An Overview of Current Knowledge of the Pupal Morphology

This paper summarizes current morphological data on pupal stages of representatives of the ‘Opatrinoid’ clade (Tenebrionidae: Tenebrioninae). Based on recovered knowledge gaps, directions for future research are provided. Additionally, pupae of three following Southern African species are described and illustrated: Gonopus tibialis (Platynotini: Platynotina), Parastizopus armaticeps (Opatrini: Stizopina) and Zadenos mulsanti (Dendarini: Melambiina).

A Sex Pheromone in the Desert Tenebrionid Beetle Parastizopus armaticeps

Males of the desert beetle Parastizopus armaticeps (Pér.) (Coleoptera: Tenebrionidae) exhibit a characteristic calling behavior that attracts females by raising the tip of the abdomen, exposing the aedeagus, and remaining in this posture for a few seconds while emitting a pheromone. We collected the pheromone by holding a solid phase microextraction fiber (100 mum polydimethylsiloxane) close to the aedeagus for 5 s and analyzed the volatiles collected by gas chromatography/mass spectrometry. The volatiles consisted of 3-methylphenol (52%), ethyl-1,4-benzoquinone (48%), and 3-ethylphenol (2%). The pheromone originated from the aedeagal glands. In the gland reservoirs, these compounds (2.1%) were mixed with ethyl, isopropyl, and propyl esters of fatty acids (24.2%), and a mixture of hydrocarbons (69.1%). The mean amount of volatiles extracted from gland reservoirs was 0.92 +/- 0.83 microg. Chemo-orientation experiments with a servosphere show that females responded only to the ternary volatile mixture. Females stopped walking, elevated the front parts of their bodies with erected antennae, turned slowly on their own axis, and walked upwind toward the odor source. Single components or binary mixtures did not elicit responses from females. Males did not respond to the pheromone. Evolutionary aspects of this pheromone system are discussed.

Defensive Secretion Components of the Host Parastizopus armaticeps as Kairomones for the Cleptoparasite Eremostibes opacus

The subsocial tenebrionid Parastizopus armaticeps Pér. is parasitized by the closely related Eremostibes opacus Koch (Coleoptera: Tenebrionidae). We found that the pygidial defensive secretions of both species are similar and contain a mixture of 1,4-benzoquinones, 1-alkenes, and monoterpene hydrocarbons. The 1-alkenes are dominated by 1-undecene, with admixtures of 1-tridecene in both species and 1-pentadecene in P. armaticeps only. Methyl- and ethyl-1,4-benzoquinone are the major quinones of the secretions of both species. The monoterpene fractions consist of (-)-alpha-pinene, (-)-camphene, sabinene, (-)-beta-pinene, and (-)-limonene. Volatiles trapped with Porapak Q at the entrance to the breeding burrows of P. armaticeps were identified as components of the defensive secretion. However, in contrast to the secretion, the 1,4-benzoquinones were almost completely absent in the volatiles. Bioassays investigating attraction showed that the cleptoparasite E. opacus was drawn to the monoterpene hydrocarbons, produced by P. armaticeps, and deterred by the 1,4-benzoquinones. The 1-alkenes had no effect. Among the monoterpenes, only (-)-camphene was attractive to E. opacus. This is one of the rare cases of chemical exploitation of defensive allomones, and the first based on odor homology. We have drawn an evolutionary scenario including various functional changes in the defensive secretion compounds, leading to the kairomonal exploitation.

Chemical mimicry of cuticular hydrocarbons – how does Eremostibes opacus gain access to breeding burrows of its host Parastizopus armaticeps (Coleoptera, Tenebrionidae)?

Breeding burrows of Parastizopus armaticeps armaticeps, a fossorial desert tenebrionid beetle, are cleptoparasitised by the closely related Eremostibes opacus. Gas chromatographic analyses show a high congruity of the cuticular hydrocarbons of both species. We compare these hydrocarbon patterns with those of four other Stizopina species and the Scaurini Herpiscius sommeri. In a bioassay, dummies treated with cuticular hydrocarbon extracts of E. opacus and the P. a. bifidus parasite E. bushmanicus were mostly ignored by P. a. armaticeps, whereas dummies with applied extracts of the remaining species were heavily attacked. We show that there is a correlation between agonistic behaviour of P. a. armaticeps towards the intruder and the chemical similarity of the cuticular hydrocarbons of the two species. Furthermore, we produced quantitatively modified hydrocarbon patterns of E. barbatus by changing the temperature at which this species was kept. The new 30 °C type was chemically similar to E. opacus, and was frequently ignored by P. a. armaticeps, whereas a reduction of the temperature to 20 °C only had minor effects on the hydrocarbon pattern. Furthermore, we show that the addition of one single component, heptacosane, to the cuticular hydrocarbon extract of E. opacus alters the host’s reaction. We discuss the role of cuticular hydrocarbons for the recognition of this host-parasite system and the relevance of quantitative characters in the hydrocarbon pattern for the discrimination of the host.

Reproductive skew and communal breeding in the subsocial beetle Parastizopus armaticeps

The monogamous beetle Parastizopus armaticeps (Tenebrionidae) constructs breeding burrows in the Kalahari Desert after rainfall, and shows extensive biparental care. However, occasional communal breeding has been reported, where the male shares the burrow with more than one female (ca. 5% of breeding burrows). We induced communal breeding in the laboratory by confining one male with two females in a small breeding cage. In 33% of these trios females stopped being aggressive towards each other and reared offspring communally. Larger females dominate smaller females, so we expected the incidence of communal breeding to be higher, and the reproductive skew to be lower, for equally sized females than for unequally sized females competing for the male. These predictions were not borne out: the incidence of communal breeding was similar in both situations and reproductive skew was independent of the (difference in) body measurements of the two females. The calculated binomial reproductive skew was in close agreement with the distribution expected from random sharing of maternity among the two females. Time spent in parental care per individual and (group) reproductive success of trios were not different from those of monogamous breeding pairs.

Individual variation and prior experience affect the discrimination of a brood-parasite by its subsocial beetle host

In birds, host experience can modify response to parasites but nothing similar is known for insects. We studied two desert tenebrionid beetles, the subsocial host Parastizopus armaticeps and its obligate and ubiquitous brood-(clepto)parasite Eremostibes opacus, which mimics the host’s odour spectrum. Nearly 10% of host burrows in the field (n=214) remain unparasitised even after introducing E. opacus experimentally (n=22). In discrimination tests, 7% of naive host beetles eject the parasite, showing individual variation in olfactory discrimination ability. To test for effects of prior breeding experience, naive (“first time”) or experienced (“second time”) breeders with or without prior parasite contact were confined with E. opacus at breeding onset, their behaviour recorded and parasite number counted on breeding completion. More first- than second-time breeding pairs completely excluded the parasite and second-time breeders with no prior contact with E. opacus had fewer parasites than any others. These pairs increased burrow-guarding dramatically, mostly during early reproduction, this being the best predictor of parasite number. Prolonged guarding, however, must be traded-off against other brood-care behaviours. Hence, it might pay breeding pairs to take the risk of accepting some parasites breeding within their burrow, and we expect this effect will be more pronounced if poor feeding and digging conditions are taken into account. This might explain why apparently 90% of the P. armaticeps breeding burrows in the field contain at least one parasitic E. opacus.

Effects of parental body condition and size on reproductive success in a tenebrionid beetle with biparental care

Abstract. 1. The beetle Parastizopus armaticeps (Coleoptera: Tenebrionidae) inhabits the Kalahari desert of southern Africa, constructs breeding burrows after rainfall, and shows extensive biparental care. Previous work has shown that it is predominantly male size, not female size, that determines breeding success; however, in the field these beetles show size assortative mating. This might obscure or override effects of female size on reproduction. Moreover, the inaccessibility of the breeding burrows makes it impossible to test effects of female and male size on offspring development and survival before adulthood.2. To disentangle the effects of male and female length, body mass, and body condition on reproductive success, males and females were paired randomly in small breeding cages in the laboratory (n = 887 breeding pairs). The construction of the breeding cages allowed a clear view of the brood chamber contents at each stage in offspring development. Larva, pupa, and imago numbers and development were monitored daily, and imago mass at hatching from the pupa (hatchlings), offspring mass, and offspring body length at complete exoskeleton melanisation (juveniles) were determined.3. There was a weak positive correlation between body condition and body length for females only. Breeding chronology was related to male body condition: males in better condition were fast to start and finish a breeding bout. Males in better condition produced heavier hatchlings and juveniles, and larger‐sized males produced larger‐sized juveniles. In contrast, numbers of larvae and juveniles produced were determined mainly by female length and body condition: larger females in better condition hatched more larvae and produced more offspring.4. The results suggest that male size and condition will be the most important determinant of reproductive success under relatively dry conditions, when burrow length is critical for reproductive success. Female size might be more important for the pair's reproductive success under wet breeding conditions, when burrow length is less critical for successful reproduction.

Reproductive skew and the threat of eviction: a new perspective

Most recent models of the partitioning of reproduction attempt to explain patterns of skew on the assumption that dominant individuals have complete control over breeding opportunities within the group, but may nevertheless concede a share of direct reproduction to subordinates as an incentive to remain peacefully in the association. Although these models may be applicable to some animal societies, we argue that they fail to provide a comprehensive theory of skew. Instead, we suggest that subordinates may often be able to claim unsanctioned reproduction for themselves, but will be forced to exercise a degree of reproductive restraint lest they incite ejection by the dominant. Reproductive skew, in other words, may reflect the threat of ejection (inducing subordinate restraint) rather than the threat of subordinate departure (inducing reproductive concessions by dominants). We present a simple ESS model of reproductive skew under these circumstances, which demonstrates that a shift in emphasis from reproductive concessions by dominants to reproductive restraint on the part of subordinates, radically alters the predictions of skew models. High group productivity, high relatedness and (when group members are related) strong ecological constraints are all expected to lead to reduced skew (the opposite conclusions to those of previous, concession-based analyses). The reason is that these factors reduce the benefits (or increase the costs) of ejection to the dominant, who therefore does best to tolerate more subordinate reproduction.

Biparental investment and reproductive success in a subsocial desert beetle: the role of maternal effort

Parastizopus armaticeps is a nocturnal subsocial detritivorous desert tenebrionid that produces very few offspring per brood. The two environmental factors that constrain reproduction, rapid sand desiccation rate and food scarcity, are countered by biparental effort. Males dig and extend breeding burrows, maintaining their moisture level; females forage on the surface at night for high-quality detritus, the larval food. This was shown to be a scarce and unpredictable resource for which there is high competition. When food was supplemented in a field experiment, offspring number and survivorship doubled and burrow failure due to desiccation dropped from approximately half, the typical failure rate for unsupplemented burrows, to zero. Food supplementation did not, however, increase larval foodstore size and there was no difference in the size of the offspring produced. Supplemented females reallocated their time, foraging less and digging more with the male. This change in maternal behaviour patterns resulted in deeper burrows which remained moist longer, thus extending the larval production period. Female foraging efficiency, particularly food retrieval speed, determined how much time females could allocate to digging, consequently increasing the reproductive success of the pair. Burrow depth and sand moisture level at the burrow base were the major correlates of reproductive success, but the scarcity and unpredictability of high-quality food on the surface and the competition for this resource influenced the number of offspring indirectly through their effect on female behaviour.

Female mate assessment tactics in a subsocial desert beetle: a test of Janetos’ models

The subsocial desert tenebrionid beetle Parastizopus armaticeps is monogamous and nocturnal, with division of labour and female mate selection for large male body size. Mate choice is time-constrained and must take place during the night following sporadic heavy rainfall since pairs can only dig breeding burrows when the sand is moist. Beetles court in small, widely-separated groups. The four tactics proposed by JANETOS (1980), through which females could assess potential mates before coming to a decision, were tested experimentally. Approximately 20% of females adopted the “fixed-threshold” tactic to assess males, all others opting for the “best of n males” tactic. These tactics are considered to be the most advantageous ones when time is limited and the number of prospective mates that can be assessed low, as is the case for P. armaticeps. Females used multiple assessments in “the best of n males tactic”, suggesting that evaluation is constrained by female information retention and integration ability, one of the constraints on sequential comparisons. This tactic also has the highest expected fitness benefits.

Odour profile congruity in two closely related desert tenebrionid beetles: Homology as the basis for a cleptoparasitic relationship?

Parastizopus armaticeps andEremostibes opacus are two closely related desert tenebrionids which also live in close association, the former having biparental brood care and the latter cleptoparasitising the brood.E. opacus is unable to discriminate between the conspecific and host odour even in the absence of physical contact. Gas chromatographic analysis of headspace volatiles of resting animals showed almost complete qualitative and quantitative odour congruity between them. Comparison of these odour profiles with those of two other tenebrionids sharing the same ecological niche,Gonopus agrestis andHerpiscius sp. (damaralis?) showed that congruity was independent of common foodplant utilisation. It is also independent of common defensive gland secretions. Parallels between resting odour spectra, defensive secretion spectra and systematic status suggest that the origins of congruity lie in odour homology, by means of which the cleptoparasite was able to exploit its host.

Ecological factors influencing burrow location,group size and mortality in a nocturnal fossorial Kalahari detritivore, Parastizopus armaticeps Peringuey (Coleoptera: Tenebrionidae)

Parastizopus armaticeps, a nocturnal detritivorous tenebrionid associated with itsmajor foodplant Lebeckia in the southern Kalahari, forms aggregations in burrows around this bush at all dune elevations. Both sexes migrate downslope after rain to breed, especially females from higher dune elevations, but not all beetles are reproductively active simultaneously. During drought, beetles inhabit deeper burrows located downslope in shaded areas and form larger groups. Mortality is highest during drought amongst beetles in shallow burrows. The importance of burrow selection for thermoregulation and associated evaporative water loss are discussed.

Behavioural adaptations to moisture as an environmental constraint in a nocturnal burrow-inhabiting Kalahari detritivore <i>Parastizopus armaticeps</i> Peringuey (Coleoptera: Tenebrionidae)

The nocturnal desert detritivore Parastiz.opus armaticeps shows differences in surface activity patterns and burrow fidelity depending on surface humidity. After rain approximately half of the beetle population, independent of sex, is highly vagile and disperses over long distances. During drought, beetles are more sedentary and show higher burrow fidelity. They also inhabit burrows that are longer and deeper than non-inhabited ones, such burrows being relatively scarce. Burrow fidelity and the adoption of a more sedentary habit during drought are considered strategies to avoid the risks of not locating a suitable burrow before sunrise and subsequent desiccation in shallow burrows.

New and Interesting Records of South African Fungi, Part VII

Four species of fungi recorded for the first time in South Africa, are described and illustrated. These are: Acremoniella verrucosa Togn. from roots of Medicago sativa; Coniella pulchella Hohn. from roots of pine-apple; Periconia igniaria Mason Ellis from seed of Medicago sativa; and Stachybotrys subsimplex Cooke from the cocoon of Parastizopus armaticeps.