Norma Elba Sánchez

Effect of two solanaceous plants on developmental and population parameters of the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

Tuta absoluta (Meyrick) is an important tomato pest that also feeds on other host-plants from the Solanceae family. We studied the effect of two cultivated plants, tomato (Lycopersicum esculentum Mill.) and potato Solanum tuberosum L. on the development and populational parameters of T. absoluta related with host-plant suitability. Larval developmental time, pupal weight, mean fecundity and an index of host-plant quality (IPQ = pupal weight / frass weight) were estimated. Age-specific survivorship and fecundity life tables were constructed in the laboratory to evaluate the following populational parameters: net reproductive rate (Ro), intrinsic rate of increase (r) and generation time (T). Larval developmental time was shorter and pupal weight was higher (P < 0.0001) for larvae reared on tomato (P < 0.0001). Mean fecundity was not significantly different on both plants (P = 0.07) and food quality of host-plant was higher for tomato (P = 0.02). Mean population parameters on tomato were: Ro = 48.92; T = 27.98, r = 0.14; and on potato: Ro = 14.43; T = 32.35, r = 0.08. Although results showed that tomato was a more suitable host-plant and had a better nutritional quality than potato, when T. absoluta fed on potato the potential population increase requires attention. Under appropriate climatic conditions, spatial and temporal coincidence between crop and pest, T. absoluta could become a pest for the potato crop.

Spatial distribution and coincidence of Neoseiulus californicus and Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) on strawberry

In strawberry greenhouses in La Plata (Buenos Aires, Argentina), Tetranychus urticae is a major pest and Neoseiulus californicus is its most important established phytoseiid predator. The purpose of this study was to determine the spatial distribution and coincidence of N. californicus and T. urticae on strawberry. T. urticae populations exhibited density variations that were followed, with some temporal delay, by those of the predator. In general terms, N. californicus exhibited lower aggregation than T. urticae. The index of dispersion (I) of T. urticae had values significantly greater than 1 in 100% of the sampling dates. The percentage of infested leaflets increased with prey density in a curvilinear way, ranging from 80 to 100% when density was higher than 100 individuals/leaflet. N. californicus had values of I higher than unity in 86.7% (G1) and 53.8% (G2) of the cases. TaylorÕs b and IwaoÕs β values were greater than 1 for both populations, this indicating aggregation. IwaoÕs results showed larger aggregation units of T. urticae (α=53.24) than of N. californicus (α=3.61), probably due to its higher fecundity and oviposition behaviour of laying eggs in clumps. Both populations were overdispersed, although in general terms, N. californicus exhibited lower aggregation than T. urticae. This would create refuges for the prey, thus increasing the persistence of the system. Index of coincidence of predator (Ic) was high most of the time even at low densities of both populations, decreased abruptly at the end of an interaction cycle and was similar at greenhouse and plant spatial scales. The high spatial coincidence of N. californicus with T. urticae suggests an important dispersal capacity of the predator and a high ability to detect leaflets with prey. The refuge index for the prey decreased with predator density and was higher at greenhouse scale than at plant scale, both at similar predator densities. At greenhouse scale and despite high predator density, the prey had a 10%-refuge, which would lead to the system persistence. Results of the present study suggest that N. californicus is a promising established natural enemy for controlling T. urticae on strawberry.

Grassland and shrubland grasshopper community composition in northern La Pampa province, Argentina

Grasshopper species composition, diversity and abundance on five grasslands and shrublands in northern La Pampa province were determined. Plant species composition, richness and a diversity index are reported for the different sites. A total of 24 grasshopper species were collected. The subfamily Melanoplinae was dominant, followed by Gomphocerinae and Acridinae. The highest abundance of grasshoppers was registered in shrubland communities in 1992. Dichroplus pratensis and Neopedies brunneri were the most abundant species in grasslands, while D. vittatus and D. pratensis were in shrublands. D. pratensis and Euplectrotettixferrugineus were broadly distributed in both community types. N. brunneri was broadly distributed in grasslands and Scyllina signatipennis in shrublands. A total of 16 species were uncommon or rare, being collected only in certain years, in low numbers, and only in some locations. Species richness and diversity indices ranged from 11-4, and from 1.680.42, respectively. Although species richness in grasslands and shrublands was similar, diversity was, in general, lower in the latter.

Potential of biological control agents against Tuta absoluta (Lepidoptera: Gelechiidae): current knowledge in Argentina

Abstract Pest suppression through biological control seeks to maximize the action of the pests natural enemies with the goal of reducing pesticide use. We present a summary of published studies and original findings on several entomophagous species as biocontrol agents of Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae), a key pest of tomato crops in Argentina, with the aim to select potential candidates for its management. Spontaneously occurring T. absoluta egg parasitism was lower than that inflicted by the larval parasitoids Dineulophus phthorimaeae (De Santis, 1983) (Hymenoptera: Eulophidae) and Pseudapanteles dignus (Muesebeck, 1938) (Hymenoptera: Braconidae). These parasitoids exhibit important life history traits in laboratory conditions and produce relevant amounts of T. absoluta mortality in the field. Surveys carried out in Tucumán and Buenos Aires provinces, Argentina, revealed that D. phthorimaeae and P. dignus coexist in tomato and eggplant crops; T. absoluta-P. dignus interaction is also found on other non-cultivated solanaceous species present in horticultural farms. In addition, studies are currently under way to determine the predation ability of Zelus obscuridorsis (Stål, 1860) (Hemiptera: Reduviidae) on both larvae and adults of the pest. Finally, we discuss the prospects for implementing experimental augmentative releases of P. dignus to control the pest, a candidate selected considering various positive biological traits and because of its simple mass production and manipulation compared with other antagonists of T. absoluta.

Life History Parameters of the Gregarious Phase of the South American locust, Schistocerca cancellata (Serville) (Orthoptera: Acrididae), under Laboratory Conditions.

A laboratory study was conducted to determine some life history parameters of the gregarious phase of the South American locust, Schistocerca cancellata. An age-specific life table was constructed based on laboratory data. Duration of egg, nymphal and adult female and male stages was 15?1.005, 33.24?1.302, 87.60+34.84, and 89.80?26.85 days, respectively. The mean life of the cohort was 175 days, and sex ratio of emerging adults was 1:1. Survivorship curve showed a high survival during most of the life time of the cohort. 9.10 % of the cohort mortality occurred during nymphal instars V and VI and 90.90 % during adult stage, most of it during the last 5 weeks. Mean fecundity was 160.7+93.10 eggs/female and the number of eggs per pod was 73+18.94. Maximum values of the fecundity rates were reached at the age of 17 and 18 weeks. The reproductive values curve indicated that the highest contribution to the future population occurred at week 17. The values of the intrinsic rate of increase (r), the net reproductive rate ( R 0) and the mean generation time ( T ) were 0.2906 _ 0.0027, 130.43 ? 9.71, and 17.78 ? 0.2281, respectively.

Trophic web associated with the South American tomato moth Tuta absoluta: implications for its conservation biological control in Argentina

The South American tomato moth Tuta absoluta is a major pest targeted for biological control by entomophagous insects. Trophic interactions among parasitoids of T. absoluta and other gelechiids feeding on crop and spontaneous wild solanaceous were investigated in north‐eastern Buenos Aires (Argentina), with the aim of assisting in the design of conservation biological control strategies. A quantitative parasitoid trophic web was constructed that included five gelechiid leafminers, five solanaceous species and a complex of 18 parasitoid species. The relative abundance of T. absoluta was highest in the Solanum melongena crop, followed by the wild plants Nicotiana glauca, Solanum americanum, Solanum sisymbriifolium and Salpichroa origanifolia. Greater parasitoid species richness associated with T. absoluta was found in the wild plants N. glauca and S. americanum. Pseudapanteles dignus was the main parasitoid of T. absoluta and co‐occurred with this pest in four plant species. Parasitism of T. absoluta by P. dignus was observed throughout the year in S. melongena, reaching values up to 33%, whereas it was sporadic and exhibited lower parasitism rates in the noncrop S. sisymbriifolium, N. glauca and S. americanum. The presence of some wild solanaceous plants should be promoted to maintain the T. absoluta– P. dignus interaction in horticultural farms.

Sexual cannibalism in the spider Alpaida veniliae (Keyserling 1865) (Araneae: Araneidae)

Abstract Postmating cannibalism where a female attacks, kills and consumes a male after a sexual encounter is frequently influenced by certain male morphological and behavioral characteristics. We conducted behavioral assays in the laboratory to test the predictions that male Alpaida veniliae (Keyserling 1865) with larger absolute and relative size in relation to their mate and those having longer courtship and copulation duration would have lower probability of being cannibalized by females after a sexual encounter. We performed a set of mating trials exposing males of different sizes to virgin females. We observed copulation in 88.8% of mating trails; its duration was very brief compared to courtship. Only a few attempts (16.7%) of recopulations with the same female were recorded, and in all these cases the first copulation was significantly shorter than the mean copulation duration of those who had only one copulation. The percentage of postcopulatory cannibalism was 47.6%. There was no correlation between the relative and absolute male size and duration of courtship and copulation. Postcopulatory cannibalism was independent of courtship and mating durations but was affected by absolute and relative male size. Smaller males were more frequently cannibalized than large ones. However, it remains unclear whether sexual cannibalism in A. veniliae may be explained by female mate choice or whether smaller males are less able to escape or defend themselves. More studies are needed to understand the underlying factors of postcopulatory cannibalism of A. veniliae, as well as to elucidate their possible ecological and evolutionary implications.