Sex determination of the live rubber plantation litter beetle, Luprops tristis: a novel method

Morphological characteristics for sexing living adults of Chaetoptelius vestitus (Coleoptera, Curculionidae)

The pistachio bark beetle, Chaetoptelius vestitus (Mulsant & Rey, 1861) is a serious pest of pistachio trees. Despite its phytosanitary importance, some aspects of its biology are still unclear. For example, determining the sex of this beetle is usually complicated by the lack of a discrete, externally visible gender-specific character. Here, the morphological characteristics of C. vestitus were studied in order to detect discriminative features for sexing living beetles. The shape of the seventh visible tergite effectively enabled the separation of the sexes. This method can be quickly learned, is non-destructive and permits sex determination of living C. vestitus adults with 100% accuracy and without damaging the insects. Sex determination using external morphology was confirmed by dissection under a stereomicroscope and by rearing experiments. These morphological criteria were further successfully verified on insects collected on seven other sites in Tunisia.

Development of a nondestructive method for sexing live adult Sternoplax souvorowiana (Coleoptera: Tenebrionidae)

The darkling beetle, Sternoplax souvorowiana (Reitter) (Coleoptera: Tenebrionidae), is flightless and lives in the Guerbantonggut desert in northwestern China. Its special eggshell structure, day-active habit, large body size, short life cycle, and ease of rearing under laboratory conditions make it an excellent model for advanced studies on desert adaptation. Determining the sex of this beetle is usually complicated by the lack of a discreet, externally visible gender-specific character. To date, dissection has been used for sex identification in this species, whereas a nondestructive means is needed for further studies of sexual dimorphism. Here, a new method based on the difference of the pigmentation pattern on the eighth tergite of each sex is described and illustrated. This method can be quickly learned, is nondestructive, is 100% accurate, and is fast enough for most applications in both the field and the laboratory. Experienced users in our laboratory routinely sex 8-10 beetles per minute.

The reproductive performance of the Mupli beetle, Luprops tristis, in relation to leaf age of the para rubber tree, Hevea brasiliensis

An analysis of host plant leaf age preferences and phenology studies led to the predictions that tender rubber plant leaves are essential for the completion of the life cycle of the Mupli beetle, Luprops tristis Fabricius (Coleoptera: Tenebrionidae) and that low tender leaf availability during the post-dormancy stage will limit the beetle population. Analyses of the effects of feeding the beetles leaves of various ages, nitrogen (N) content, and moisture content on fecundity and the duration of post-dormancy survival were carried out. The results showed that tender leaf availability during the post-dormancy phase of L. tristis is a critical factor that determines the survival of L. tristis adults and the subsequent generation. The control of powdery mildew ( Odium hevea) disease-mediated premature leaf fall in rubber plantations may regulate the beetle population. A peak in fecundity during the early phase of post-dormancy is proposed as an adaptive mechanism of L. tristis to synchronize egg production and feeding with tender leaf availability in rubber plantations. Variations in nutrient levels and moisture content between deciduous rubber tree leaves of different ages are attributed to the leaf nutrient resorption mechanism of senescing leaves. These results established that tender leaves with high N and moisture levels are essential for post-dormancy survival and that N influences fecundity. The results of the experiments could aid decision making regarding the population management and control of L. tristis in rubber plantations.

Sexing live pupae and adults of two wax blooming beetles, Colposcelis microderoides microderoides and Anatolica polita borealis

The wax blooming beetles Colposcelis microderoides microderoides Reitter and Anatolica polita borealis Kaszab (Coleoptera: Tenebrionidae) are small, flightless beetles living in the Guerbantonggut desert in the northwestern region of China. These beetles were recently found to have wax blooms, and their short life cycle and ease of rearing under laboratory conditions make them excellent models for advanced studies on desert adaptation. To date, dissection has been used for sex identification in these species, whereas a nondestructive method is needed for further studies on sexual dimorphism. Microscopic examinations of pupae and adults revealed distinct differences between the sexes in the 8th abdominal sternites, including the presence of a setose cleft in adult males that is not visible in females, in which the 8th sternite forms a single semicircular plate. The female pupae have a pair of tan papillae and a tan genital orifice, which are absent on the male 8th sternite. These two sexual characteristics can be used to sex live adults and pupae. These methods are simple, nondestructive, 100% accurate, and useful for sex differentiation of dead beetles and some other tenebrionid species (including some pests) in both the field and the laboratory.

Defensive glands in the adult and larval stages of the darkling beetle, Luprops tristis

Invasion by large populations of the litter-dwelling darkling beetle Luprops tristis Fabricius (Coleoptera: Tenebrionidae) following the short spell of summer rains during April, and their extended state of dormancy is a regular event in rubber plantation habitats in south-western India. Strong smelling secretions of the beetle cause blisters on skin of human beings. Such secretions appear defensive because they appear to facilitate their avoidance by other predatory organisms. Defensive glands in the larvae and adults of L. tristis are described, as well as the mode of eversion of the glands. The glands in larvae consist of two pairs of noneversible glands in a conical depression on the 2(nd) and 3(rd) sternites, whereas in adults only one pair occurs between 7(th) and 8(th) sternal segments. These glands may be a major reason for avoidance of larvae and adults by their natural enemies and their very high numbers in the litter of rubber plantations.

Population dynamics of the rubber plantation litter beetle Luprops tristis, in relation to annual cycle of foliage phenology of its host, the para rubber tree, Hevea brasiliensis

The population dynamics of the rubber plantation litter beetle, Luprops tristis Fabricius 1801 (Coleoptera: Tenebrionidae) was assessed in relation to the phenology of leaf shedding and defoliation pattern of para rubber trees, Hevea brasiliensis Müll. Arg (Malpighiales: Euphorbiaceae), during a two year study period. The abundance of adults, larvae and pupae per 1m(2) of litter sample was recorded. Post dormancy beetles appeared in leaf litter following annual leaf shedding, whereas larvae, pupae and teneral adults were present after leaf flush. No stages were recorded from plantations following the summer rains until the annual litter fall in the next season. Parental adults peaked at the time of leaf sprouting and tender leaf fall. Larvae and teneral adults peaked at the time of premature fall of green leaves and flowers. Teneral adults of six age classes were recorded and all entered dormancy irrespective of the feeding time available to each age class. Females outnumbered males in the parent generation, while the sex ratio of new generation adults was not biased towards either sex. The phenological stages of rubber trees included leaf fall in late December and early January, leaf sprouting and new leaf production in January and flowering in February. All feeding stages of L. tristis peaked in abundance when premature leaves are most abundant in the leaf litter. Prediction of the timing of appearance of various developmental stages of L. tristis in plantations, invasion into buildings and intensity of population build up in rubber belts is possible by tracking the phenology of leaf fall in rubber plantations, time of return of post dormancy adults and the onset of summer rainfall. Perfect synchrony was recorded between the field return of parental adults with annual leaf shedding, the oviposition phase of parental adults with tender leaf fall at the time of leaf sprouting, and larval and teneral adult stages with premature fall of leaves. Premature leaf availability is suggested as contributing to the reproductive efficiency of parental adults, the survival of early developmental stages and of new generation adults during dormancy.

Life history, aggregation and dormancy of the rubber plantation litter beetle, Luprops tristis, from the rubber plantations of moist south Western Ghats

Life history, aggregation and dormancy of rubber plantation litter beetle Luprops tristis Fabricius, (Tenebrionidae: Coleoptera) is described from rubber plantation belts in the western slopes of Western Ghats from the south Indian state of Kerala. The life cycle lasted 12 months, including the 5 larval instars lasting 1 month, the 3 day pupal stage, and the adult stage that can last 11 months. The adult stage includes an inactive dormancy phase of 9 months in shelters and 1 month each of active pre-dormancy (feeding) and post-dormancy (feeding and reproduction) phases that occur in rubber plantation litter. Reproductive activities are confined to the post-dormancy phase. With the onset of summer rains, huge aggregations of adults invade residential buildings and enter into a state of dormancy for 9 months. Beetle aggregations were in the range of 0.5 million to 4.5 million individuals per residential building. Dormancy in L. tristis is best classified as oligopause, which is intermediate between quiescence and diapause. Adults and larvae feed preferentially on wilted rubber tree leaves. Age-specific variation in mortality during dormancy is distinct with higher survivability for adults that have a longer pre-dormancy period. Generations are non-overlapping.