Estimating the intrinsic rate of increase of Tetranychus urticae: which is the minimum number of immature individuals to consider?

The relationship between the number of immature individuals of Tetranychus urticae used to calculate life table parameters (sex ratio, development time, immature survival and the intrinsic rate of increase) and the accuracy of such determinations has been estimated. Additionally, the approach used in this paper, which considers each female offspring as a separate replicate, has allowed statistical comparison of the parameters obtained. At least the first four eggs from 16 females should be followed up to completion of their development to prevent the occurrence significant differences for the selected parameters. However, our results indicate that optimal sample sizes are different for the different life table parameters considered and should adapt to the preset level of accuracy.     

Economic threshold for Tetranychus urticae (Acari: Tetranychidae) in clementine mandarins Citrus clementina

Tetranychus urticae is a key pest of citrus in Spain, especially of clementine mandarin trees. The effects of this mite on fruit production were assessed in 24 clementine trees for three consecutive years. Trees were visited weekly and spider mite and phytoseiid mite populations and leaf flush patterns were estimated. At the end of the season, mandarins were harvested, weighed, and mite damage (scarring on the fruit) characterized. Negative relationships between spider mite density and yield (kg/tree) and fruit damage (% scarred fruit rind) were found. The multivariate regressions highlighted the key role of phytoseiid mites and leaf flush patterns, which were negatively related to fruit damage. The shortest sampling period that satisfactorily predicted fruit damage at harvest, extended from August to mid-October. For IPM purposes, an action threshold of 31.1 mites m^?2 of symptomatic leaf was estimated. Taking into account spider mite dynamics, the economic threshold ranged from 10 to 15 mites m^?2 of symptomatic leaf. When this threshold is exceeded growers would have a 1-week window to apply the control technologies against T. urticae of their choice.     

Thermal requirements of Fidiobia dominica (Hymenoptera: Platygastridae) and Haeckeliania sperata (Hymenoptera: Trichogrammatidae), two exotic egg parasitoids of Diaprepes abbreviatus (Coleoptera: Curculionidae)

Diaprepes abbreviatus is an exotic root weevil occurring in southern US. It is a highly polyphagous species which can complete its entire life cycle on citrus and several woody ornamental plants. The lack of native egg parasitoids for this weevil in citrus orchards has triggered efforts to evaluate candidate egg parasitoids from the Caribbean Region into Florida. The egg parasitoids Fidiobia dominica and Haeckeliania sperata are two exotic natural enemies of D. abbreviatus recently introduced in the US in a classical biological control program. The thermal requirements of both parasitoids were studied in the laboratory. The upper development threshold (UDT) of F. dominica was 30.0°C, its maximal development rate (MDR) occurred at 27.6°C, its lower development threshold (LDT) was 9.6°C and its thermal constant (K) for development from egg to adult was 293.1 DD. For H. sperata, UDT was 35.0°C, MDR occurred at 31.0°C, LDT was around 15°C and K was 188.1 DD. Based on these results, both species would be able to complete 17 to 18 generations annually in southern Florida. However, host availability during critical periods could severely impair the ability of these egg parasitoids to establish and successfully control D. abbreviatus in areas where winter temperatures fluctuate around 12°C, the LDT for this pest.     

Centaurea prolongi and C. crocata in Portugal: an old confusion

Centaurea crocata , described in 1984 from the Serra de Monchique in the Algarve (S Portugal), has a long history of confusion with C. prolongi from S Spain. From the study of herbarium specimens and of living plants, authors conclude that all previous Portuguese citations of C. prolongi belong actually to C. crocata . However, authors' studies confirm the real presence of C. prolongi in some relictic localities in the limestones of the extreme south of the Algarve. A morphologic comparison between the two species is performed and authors suggest for C. crocata a hypothetical hybrid origin between C. prolongi and a species of sect. Chamaecyanus .     

The hyperhydricity ofin vitroregenerants of grass pea (Lathyrus sativus L.) is linked with an abnormal DNA content

The grass pea (Lathyrus sativus) is a wild relative of the protein pea which may be a useful genetic resource for the acquisition of interesting stress resistance traits. However, grass pea is cross incompatible with pea, leaving protoplast fusion as the only alternative to produce interspecific hybrids of grass pea and pea. In addition, as all grass pea seeds contain a toxic aminoacid, low-toxin containing genotypes will have to be produced by gene transfer. In this context, it is therefore essential that regenerated plants are fertile, true-to-type and not chimaeric in nature when they have been obtained in absence of any selection treatment. In the present study, shoot buds were regenerated from hypocotyls of three grass pea genotypes, and flow cytometry permitted us to characterise them in terms of nuclear DNA content. Plant regeneration competence was genotype-dependent and strongly also was correlated with a normal DNA content. The auxin/cytokinin balance of regeneration media affected the DNA level of regenerants. In turn, an abnormal DNA content was systematically associated with severe hyperhydricity symptoms, which hampered the regeneration of rooted, fertile plants.     

Flow cytometry distinction between species and between landraces within Lathyrus species and assessment of true-to-typeness of in vitro regenerants

The genus Lathyrus includes a number of neglected wild relatives of pea with potential as genetic resources for acquisition of stress resistance traits, but, due to little breeding, genotypes under culture are mainly landraces and seldom true varieties. Development of in vitro approaches for Lathyrus is also limited, and assessments of nuclear DNA content, for taxonomical or breeding purposes, are sparse. Genome size and AT/GC ratio were determined by flow cytometry, allowing for distinction between protein and forage L. sativus, L. cicera, L. ochrus and L. clymenum and the ornamental sweet pea (L. odoratus), and also between landraces within L. sativus L. and L. cicera L. In addition, explants from in vitro seedlings of eight genotypes from the five Lathyrus species above were cultivated in vitro, plant regeneration was achieved for all landraces and species, and the nuclear DNA content of the regenerants was compared with that of their mother plants, whereby the true-to-typeness of such regenerants was confirmed.