Evidence of formation of glushinskite as a biomineral in a Cactaceae species

The X-ray diffractometric and infrared spectroscopic investigation of crystalline material isolated from the Cactaceae species Opuntia ellisiana shows the presence of a very complex mineral composition, including whewellite (monohydrated calcium oxalate), opal (SiO2), calcite (CaCO3) and glushinskite (dihydrated magnesium oxalate). This is the first report of the presence of magnesium oxalate in plants.     

Effects of shade, drought and daughter cladodes on the CO2 uptake by cladodes of Opuntia ficus-indica

The effects of shade on the physiology of opuntias have received little attention, notwithstanding that shade regularly occurs in both wild stands and cultivated populations. This research evaluates the effects of shade on the physiology of cladodes of Opuntia ficus‐indica, with and without daughter cladodes, as they are exposed to progressive drought. The stress caused by shade, drought and daughter cladodes reduced photosynthesis by mother cladodes and was associated with decreases in relative water content, parenchyma thickness and chlorophyll content. Shade exacerbated the physiological drought of mother cladodes imposed by daughter cladodes and by reduced soil water content.     

Morphological and phytochemical aspects of three alien Opuntia species on Euganean Hills in North-Eastern Italy

In this study, Opuntia stricta, O. engelmannii, and O. humifusa, naturalized alien units in the Euganean Hills (North-Eastern Italy), are investigated. Different morphological and physiological features both in cladodes collected in summer and winter and in fruits arisen from two blooms are reported. The morphological observations showed a different organization in epidermis/hypodermis of cladodes collected in winter and in summer, probably correlated to the individual plant reaction to a stressful factor as low temperature. Scanning electron microscopy observations revealed no differences in the deposition of waxes and stomata distribution in the epidermis of cladodes. The betacyanin analysis showed that cladodes produce these pigments only in the winter season. In all the species, the higher content of betacyanins was reached in the fruits from the second bloom, with O. stricta being the most rich. The amount of betacyanins is comparable to some commercial red beets used as a common source of betacyanins as natural food color.     

A comparison in species distribution model performance of succulents using key species and subsets of environmental predictors

Identifying the environmental drivers of the global distribution of succulent plants using the Crassulacean acid metabolism pathway of photosynthesis has previously been investigated through ensemble‐modeling of species delimiting the realized niche of the natural succulent biome. An alternative approach, which may provide further insight into the fundamental niche of succulent plants in the absence of dispersal limitation, is to model the distribution of selected species that are globally widespread and have become naturalized far beyond their native habitats. This could be of interest, for example, in defining areas that may be suitable for cultivation of alternative crops resilient to future climate change. We therefore explored the performance of climate‐only species distribution models (SDMs) in predicting the drivers and distribution of two widespread CAM plants, Opuntia ficus‐indica and Euphorbia tirucalli. Using two different algorithms and five predictor sets, we created distribution models for these exemplar species and produced an updated map of global inter‐annual rainfall predictability. No single predictor set produced markedly more accurate models, with the basic bioclim‐only predictor set marginally out‐performing combinations with additional predictors. Minimum temperature of the coldest month was the single most important variable in determining spatial distribution, but additional predictors such as precipitation and inter‐annual precipitation variability were also important in explaining the differences in spatial predictions between SDMs. When compared against previous projections, an a posteriori approach correctly does not predict distributions in areas of ecophysiological tolerance yet known absence (e.g., due to biotic competition). An updated map of inter‐annual rainfall predictability has successfully identified regions known to be depauperate in succulent plants. High model performance metrics suggest that the majority of potentially suitable regions for these species are predicted by these models with a limited number of climate predictors, and there is no benefit in expanding model complexity and increasing the potential for overfitting.     

Growth and Reproduction in Forest Trees of the Cactus Opuntia excelsa1

In southwestern México, the number of new cladodes on Opuntia excelsa was a skewed bell-shaped function of size (“size” being the number of cladodes persisting from previous years). Fruit number was a sigmoidal function of size, but the number of seeds per fruit was independent of number of fruits per plant. The curves for production of new cladodes and of fruits both showed maximum increase for plants with 150–350 cladodes, when the crowns were reaching or in the canopy. New cladode production declined at about the size where reproduction plateaued; we suggest this was due to limitation of crown dimensions by mechanical and physiological factors.     

Potential Non-target Effects of a Biological Control Agent, Prickly Pear Moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), in North America, and Possible Management Actions

Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), the poster child of biological control, has recently invaded the United States. The first US record was at Big Pine Key, Florida, in 1989. Since then it has moved rapidly northward into South Carolina. Fears are high that it will disperse, either on its own, or with human help, into the US desert southwest and Mexico. There are at least 31 species of prickly pear in the US that are likely to be attacked by Cactoblastis and 56 species in Mexico. As well as the threat to wild cacti, there are over 250,000 ha of Opuntia plantations in Mexico that support a thriving agricultural industry, most of which is centered on harvesting fruits or pads. Possible control measures include classical biological control using parasitoids or pathogens from South America, chemical control or F₁ sterility, as has been used successfully for the codling moth. However, most of these options appear to have insurmountable difficulties. Classical biological control raises the fear of further non-target effects of natural enemies on native cactus herbivores. Chemical control has potential non-target effects on other (rare) insects and is expensive. F₁ sterility is also expensive and is not self-sustaining, requiring considerable and continual human input. Nevertheless, research on control options is vital as is further work on the rate of spread and impact of Cactoblastis in the United States Southeast, so that we can be as well prepared as possible to deal with this threat when it arrives in Arizona, California, and Mexico.     

Reproductive ecology and inbreeding depression in Opuntia rastrera (Cactaceae) in the Chihuahuan Desert: Why are sexually derived recruitments so rare?

We evaluated the influence of the reproductive ecology on low recruitment of sexually derived progeny observed in Opuntia rastrera Weber in the Southern Chihuahuan Desert, in two vegetation types. The flowers are diurnal, remaining open 9–10 hr. Pollen is released in the morning and at the same time the stigmas become receptive. Nectar is produced all day, but the production rate is higher at noon. The flowers are visited by insects, mainly solitary bees (Diadasia sp. and Lithurge sp.). Floral characteristics and the pollen/ovule ratio suggest that Opuntia rastrera is a facultative xenogamous species. Controlled pollinations indicate that it is not apomictic and pollinators are required to set fruit; it is also self-compatible, but there is strong inbreeding depression for fruit set. However, we were unable to demonstrate differences in reproductive characters between the populations in both vegetation types. The average density of adults per hectare was one order of magnitude higher in the nopalera (Opuntia-dominated scrublands) than in the grassland. However, the average density of plants that originated from seeds was one order of magnitude lower in the nopalera. Opuntia rastrera produces abundant flowers, fruits, and seeds in both vegetation types in natural conditions. The low success in the recruitment of new genets cannot be ascribed to the reproductive ecology.     

The effects of simulated rainfall on cochineal insects (Homoptera: Dactylopiidae): colony composition and survival on cactus cladodes

ABSTRACT. 1. A rainfall simulator is described that was used to investigate the effects of rainfall on the cochineal insect Dactylopius opuntiae (Cockerell). This species occurs in discrete colonies that are protected by a copious covering of opaque'woolly'wax, and is the most important biological control agent of the prickly pear cactus, Opuntia ficus-indica (L.) Miller, in South Africa.
2. We record the composition of cochineal colonies (stage and number of individuals) in relation to colony size to allow accurate predictions of colony composition from size measurements of the intact, wax-covered colonies before their exposure to rainfall.
3. Even short exposures (15 min) to simulated rainfall (delivered at a rate of about 50 mm/h) resulted in wax erosion, and the effect was most marked in small, recently established colonies. Coverings of compacted wax protected the mature colonies from erosion.
4. The number of colonies that were washed off the plant was a function of colony size and the duration of exposure to simulated rainfall. Most of the small, recently established colonies were washed from the plants after 120 min. All of the large, mature colonies, albeit badly mutilated and containing far fewer individuals, remained on the plants even after 240 min exposure.
5. Survival of individuals, in colonies of all sizes, was less than about 40% after short bouts of rainfall (30 min). First- and second-instar individuals accounted for most of the observed mortalities, and mortality of all stages increased with increasing rainfall duration.
6. These observations provide a partial explanation for the poor performance of D. opuntiae as a biological control agent of cacti in higher-rainfall areas.