The Endangered Species <em>Dioon edule</em> in the Sierra Madre Oriental in San Luis Potosí: Demography and Genetic Diversity

The distribution of the endangered species Dioon edule is in populations scattered throughout the Sierra Madre Oriental in San Luis Potosí, Mexico. Its habitat is tropical dry forests at lower elevations and oak forests at higher elevations, mainly disturbed by anthropic activities. We determined and analyzed nine populations’ demographic structure and explored the genetic diversity of five using SSR markers. The population density averaged 2050 individuals ha-1 and have an aggregated distribution pattern. Differences in the plants’ size among localities are due to site quality, based on their adaptation capacity and response to climate and soil traits. Most populations have the highest mortality in the early stages of life, with a low mortality rate for those who survive this bottleneck. Two populations have a relatively constant mortality rate, attributed to disturbance of the habitat. The populations show low genetic diversity and an excess of homozygotes. Their similarity is probably related to the formation of natural corridors favoring connectivity between populations. The deterioration and fragmentation of the habitat have severe effects on the populations’ viability, like reducing gene flow, which has led to inbreeding and genetic drift

Insect juvenile hormone III in the sedge, Cyperus iria L.: Distribution, biosynthesis and possible biological function(s)

grantor: University of TorontoIn insects, juvenile hormones regulate critical physiological processes such as metamorphosis and reproduction. To date, there has been only one report of the identification of an insect juvenile hormone in a plant; juvenile hormone III (JH III) has been isolated from the sedges 'Cyperus iria' L. and 'C. aromaticus' (Ridley) Mattf and Kûk. The presence of these compounds in plants is not understood. The temporal and tissue distribution of JH III was determined in ' C. iria' over an eight-month period, from the seedling to senescent plant. Levels increased in immature plants until flowering, at which time a transient decrease in JH III content of all plant tissues was observed. Juvenile hormone III subsequently increased in mature plants until senescence when, again, amounts fell in the aerial tissues. This pattern was not observed in the subterranean tissues, where JH III was predominantly localized. The high levels of this unique compound throughout development suggests that JH III may have an important biological function in 'C. iria'. The ability of this plant to interfere with insect development, presumably because of the presence of JH III, has been demonstrated. However, conclusive evidence of the protection of the plant from insect herbivory by this compound has not been established. Therefore, other potential biological activities were investigated. Juvenile hormone III delayed lettuce seed germination and demonstrated potent inhibitory activity against rice seedling growth. This activity may confer an ecological advantage to 'C. iria' by affecting the germination and growth of neighbouring, competing plants. The antimicrobial activity of JH III (13.3 [mu]g) was tested on a taxonomically diverse range of fungi; no cytotoxic effect was observed. At present, little is known about the biosynthesis of JH III in ' C. iria'. To elucidate this pathway, a cell suspension culture of 'C. iria' was established. Through enzyme inhibition studies, it has been conclusively demonstrated that the sesquiterpenoid skeleton of JH III is biosynthesized, at least partially, through the classical mevalonate pathway. Precursor feeding studies also suggest that the later steps of the biosynthetic pathway are similar to the insect pathway.Ph.D

Caterpillar salivary enzymes: "eliciting" a response

Plants exhibit remarkable plasticity in their ability to differentiate between herbivorous insect species and subtly adjust their defense responses to target distinct pests. One key mechanism used by plants to recognize herbivorous caterpillars is elicitors present in their oral secretions; however, these elicitors not only cause the induction of plant defenses but recent evidence suggests that they may also suppress plant responses. The absence of “expected changes” in induced defense responses of insect-infested plants has been attributed to hydrogen peroxide produced by caterpillar salivary glucose oxidase (GOX). Activity of this enzyme is variable among caterpillar species; it was detected in two generalist caterpillars, the beet armyworm (Spodoptera exigua) and the bertha armyworm (Mamestra configurata), but not in other generalist or specialist caterpillar species tested. In the beet armyworm, GOX activity fluctuated over larval development with high activity associated with the salivary glands of fourth instars. Larval salivary GOX activity of the beet armyworm and the bertha armyworm was observed to be significantly higher in caterpillars reared on artificial diet as compared with those reared on Medicago truncatula plants. This implies that a factor in the diet is involved in the regulation of caterpillar salivary enzyme activity. Therefore, plant diet may be regulating caterpillar oral elicitors that are involved in the regulation of plant defense responses: our goal is to understand these two processes.Les plantes font montre d’une remarquable plasticité pour distinguer différentes espèces d’insectes herbivores et subtilement ajuster leurs réponses de défense en fonction des différents ravageurs. Les éliciteurs présents dans les sécrétions orales constituent un mécanisme clé utilisé par les plantes pour reconnaître les chenilles herbivores; cependant, ces éliciteurs, non seulement provoquent-ils l’induction des défenses de la plante, mais des preuves récentes suggèrent qu’ils pourraient aussi inhiber les réponses de la plante. L’absence de « changements attendus » en guise de réponses de défense chez des plantes infestées d’insectes a été attribuée au peroxyde d’hydrogène produit par la glucose oxydase (GOX) salivaire de la chenille. L’activité de cette enzyme varie selon l’espèce de chenille; elle fut détectée chez deux espèces de chenilles généralistes, la légionnaire de la betterave (Spodoptera exigua) et la légionnaire bertha (Mamestra configurata), mais pas chez les autres espèces de chenilles généralistes ou spécialistes testées. Chez la légionnaire de la betterave, l’activité de la GOX fluctua pendant le développement larvaire avec une forte activité associée aux glandes salivaires du 4e stade larvaire. On observa que l’activité salivaire de la GOX chez les larves de la légionnaire de la betterave et chez la légionnaire bertha était significativement plus élevée chez les chenilles élevées sur un milieu nutritif artificiel que chez celles élevées sur des Medicago truncatula. Ceci suppose qu’un facteur du régime alimentaire est impliqué dans la régulation de l’activité des enzymes salivaires des chenilles. Par conséquent, le régime alimentaire végétal pourrait réguler les éliciteurs oraux de la chenille qui seraient impliqués dans la régulation des réponses de défense de la plante : notre but est de comprendre ces deux processus

Activity of insect juvenile hormone III: seed germination and seedling growth studies

Juvenile hormones are sesquiterpenoids that regulate developmental processses such as metamorphosis and reproduction in insects. Insect juvenile hormone III (JH III), methyl-10R,11-epoxy-3,7,11-trimethyl- 2E,6E-dodecadienoate, has also been identified in two sedge species, Cyperus iria and C. aromaticus (Toong et al. 1988). Potential allelopathic activity of this compound and the structurally related sesquiterpenoid farnesol was investigated using seed germination and seedling growth assays with radish, lettuce and rice. Treatment of seeds with JH III delayed lettuce seed germination and potently inhibited rice shoot growth. Both farnesol and JH III inhibited the growth of C. iria seedlings. The antimicrobial activity of JH III was also tested on a taxonomic and ecologically diverse range of fungi. Using the classic cytotoxic disk assay, JH III did not effect growth of the fungal species tested. We believe that JH III may contribute to the aggressive nature of this invasive weed species

Flesh flies (Diptera: Sarcophagidae) attracted to dog-day cicada (Neotibicen canicularis (Harris) Hemiptera: Cicadidae) carcasses in Québec, Canada

This study was carried out to determine the diversity of Diptera attracted to carcasses of dog-day cicadas, Neotibicen canicularis (Harris) (Hemiptera: Cicadidae), during the late summer of 2019 in Montréal, Québec, Canada. Only sarcophagid larvae were found in cicada carcasses and were maintained until pupariation for species identification. Emerged specimens were identified as Emblemasoma albicoma Reinhard, Emblemasoma erro Aldrich, Helicobia rapax (Walker), Sarcophaga (Liosarcophaga) sarracenioides Aldrich, and Sarcophaga (Wohlfahrtiopsis) utilis Aldrich. These results provide new insight into the feeding habits of these species. Also, despite their wide range of rearing records, H. rapax, S. sarracenioides, and S. utilis have never been associated with N. canicularis, and this association is published here for the first time. Finally, this is the first record of E. erro in Québec and of E. erro utilizing N. canicularis as a host

Influence of diet on the larval beet armyworm, Spodoptera exigua, glucose oxidase activity

Many researchers investigating plant-insect interactions maintain their insect colonies on artificial diet and assume that salivary enzymes and elicitors remain representative of natural situations. These salivary elicitors, such as the enzyme glucose oxidase (GOX), play important roles in influencing plant defense responses. In fact, GOX has been implicated in suppressing induced nicotine-production in tobacco plants (Musser et al., 2002). [...] When 4th instar plant-fed caterpillars were transferred to artificial diet, increased labial salivary GOX activity is closely correlated with the amount of time spent feeding on artificial diet. This study shows that the labial salivary GOX activity of S. exigua caterpillars is dependent on diet and developmental stage and that caution must be exercised in the design of plant-insect experiments