Norma E. Sánchez

Effect of Tomato Leaf Hairiness on Functional and Numerical Response of Neoseiulus Californicus (Acari: Phytoseiidae)

The objective of this study was to determine whether differences in hairiness of tomato plants affect the functional and numerical response of the predator Neoseiulus californicus McGregor attacking the two-spotted spider mite, Tetranychus urticae Koch. Two tomato hybrids with different density of glandular hairs were used. The functional response was measured by offering eggs and adults of T. urticae at densities ranging from 4 to 64 items per tomato leaflet (surface ca. 6.3 cm2); eggs were offered to predator protonymphs and deutonymphs, adult spider mites to adult predators. The number of spider mites eaten as a function of initial density was fitted to the disc equation. Predator densities were regressed against initial prey densities to analyze the numerical response. The number of eggs and adults of T. urticae eaten by N. californicus was extremely low in both hybrids. The nymphal stage of N. californicus and prey density had a significant effect on the number of T. urticae eggs eaten by the predator, while hybrid had no effect. The functional response fitted reasonably well to the Holling model. The handling time (Th) and the attack rate (a) were very similar among the two hybrids. The numerical response indicated that the absolute density of predators increased with changes in spider mite densities but the relative predator/prey density decreased in both hybrids. Tomato hairiness prevented N. californicus from exhibiting a strong numerical response and the predator functional response was much lower than observed in other host plants and other phytoseiids. This result shows the need to consider plant attributes as an essential and interactive component of biological control practices.

Neoseiulus californicus (Acari: Phytoseiidae) as a potential control agent of Tetranychus urticae (Acari: Tetranychidae): effect of pest/predator ratio on pest abundance on strawberry.

Neoseiulus californicus (McGregor) is a promising agent for successful Tetranychus urticae Koch control through conservation techniques, in strawberry crops in La Plata (Buenos Aires, Argentina). In prey–predator interaction, initial relative densities have an important effect on system dynamics. The economic threshold level (ETL) used for this pest in the present study was 50 active mites per leaflet. In our laboratory experiments, initial T. urticae to N. californicus ratio had a significant effect on the population abundance of T. urticae at a 7-day period. When pest/predator ratio was 5/1 (at initial pest densities from 5 to 15 females/leaflet) the final number of active T. urticae/leaflet was significantly lower than the ETL, while at 20 females/leaflet this number did not differ from the ETL. At 7.5/1 ratio, the final number of active T. urticae/leaflet, at initial pest densities from 5 to 15 females/leaflet, reached the ETL without surpassing it. At 10/1 and 15/1 ratios, pest densities exceeded the ETL only at 15 initial T. urticae/leaflet. Most greenhouse and field observations were consistent with the predictions of a graphical model based on experimental results. This predator was very effective in limiting pest densities at a 7-day period and within the range of pest–predator ratios and absolute densities used in this study. Conservation of N. californicus promoting favorable pest/predator ratios may result in early control of T. urticae.

Effects of the herbicide glyphosate on biological attributes of Alpaida veniliae (Araneae, Araneidae), in laboratory.

In the past decades there has been increasing interest in the study of arthropod predators as effective potential natural enemies to be used in the biological control of agricultural pests. In Argentina, transgenic soybean crops (Round-up Ready, RR) are inhabit by many spider species, some of them in high abundance, being indicative of an import potential for pest predation. This crop is associated with the use of glyphosate, a broad-spectrum herbicide, with low environmental impact, even though since the 80s, several negative effects have been deeply documented on mammals, fishes, amphibians, snails, earthworms, insects, etc. Nowadays, the effects on arthropod physiology, behavior and life history traits as end-points in ecotoxicological evaluations are being recognized. In transgenic soybean crops of Buenos Aires province (Argentina), Alpaida veniliae (Araneae, Araneidae) is one of the most abundant orb web weaver spiders. The purpose of this study was to address the effects of glyphosate on some biological attributes of A. veniliae, in laboratory. Results of this study showed no lethal direct effects of Glifoglex on this spider, but it is the first report in literature about sublethal effects of this herbicide on a spiders biological attributes. Negative effects on prey consumption, web building, fecundity, fertility and developmental time of progeny were observed. Although sublethal effects have received less attention than direct lethal effects, they are relevant from an ecological point of view, since the reduction of the arthropod performance may create risks to arthropod biodiversity conservation in agroecosystems.

Parasitism of Tuta absoluta (Lepidoptera, Gelechiidae) by Pseudapanteles dignus (Hymenoptera, Braconidae) Under Laboratory Conditions

Abstract Laboratory studies were conducted to measure selected life history traits and the functional response of the parasitoid Pseudapanteles dignus (Muesebeck), a major enemy of Tuta absoluta (Meyrick) in tomato crops in South America. Newly mated P. dignus females were individually exposed to 10 host larvae in mines for 24 h. We determined developmental time from egg to pupal formation and pupal stage duration, female adult life span, fecundity, reproductive period, daily parasitism rate, and sex ratio of offspring. For the functional response experiment, treatments consisted of six host densities: 3, 5, 7, 10, 15, 20, or 30 larvae. The number and proportion of parasitized hosts were calculated for each density. The shape of the functional response curve was analyzed by logistic regression. P. dignus females attacked hosts daily, exhibiting modest lifetime fecundity (≈32 parasitized hosts per female) and a female-biased offspring sex ratio. Female adult life span was 36 d. P. dignus showed a type I functional response within the range of host densities tested. We observed that females detect and parasitize the host within a wide range of densities, including low densities. The functional response curve reached an asymptote at a mean density of six hosts per day and seemed not to be egg-limited. Percent parasitism was ≈30%. The ecological implications of the results in relation to the potential of P. dignus for the biological control of T. absoluta in tomato are discussed.

Chapter Two – Pesticides Used in South American GMO-Based Agriculture: A Review of Their Effects on Humans and Animal Models

In South America, the incorporation of genetically modified organisms (GMO) engineered to be resistant to pesticides changed the agricultural model into one dependent on the massive use of agrochemicals. Different pesticides are used in response to the demands of the global consuming market to control weeds, herbivorous arthropods, and crop diseases. Here, we review their effects on humans and animal models, in terms of genotoxicity, teratogenicity, and cell damage. We also stress the importance of biomarkers for medical surveillance of populations at risk and propose the use of biosensors as sensitive resources to detect undesirable effects of new molecules and environmental pollutants. The compatibility of glyphosate, the most intensively used herbicide associated to GMO crops, with an integrated pest management for soybean crops, is also discussed.

Spatial Patterns of Parasitism of the Solitary Parasitoid Pseudapanteles dignus (Hymenoptera: Braconidae) on Tuta absoluta (Lepidoptera: Gelechiidae)

We examined the interaction between the tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a key pest of tomato crops in South America, and its main solitary larval parasitoid, Pseudapanteles dignus (Muesebeck) (Hymenoptera: Braconidae). The pattern of parasitism of T. absoluta by the parasitoid was studied at three scales on tomato crops: plant, leaf, and leaflet. Host density, spatial distributions of both host and parasitoid, percentages of parasitism, variation in the probability and risk of parasitism in relation to host density, and the spatial density dependence were assessed in a horticultural region in Argentina. The spatial distribution of T. absoluta was clumped at all sites and scales, whereas that of P. dignus was much more variable, fitting to negative, positive binomial distributions and to Poisson series. Percentages of parasitism were as follows: site 1, 17.06%; site 2, 27.53%; site 3, 26.47%; site 4, 45.95%. Parasitoid aggregation in relation to host density was found at leaf and leaflet scales. However, the proportion of parasitized hosts was independent of host density. The variability of parasitism rates exhibited at the three spatial scales seems to result in partial refuges for the host, which might contribute to the persistence of the interaction between host and parasitoid. We discuss our field observations in relation to ecological theory and its potential application to the biological control of T. absoluta on tomato.

Biology of Dineulophus phtorimaeae (Hymenoptera: Eulophidae) and Field Interaction with Pseudapanteles dignus (Hymenoptera: Braconidae), Larval Parasitoids of Tuta absoluta (Lepidoptera: Gelechiidae) in Tomato

ABSTRACT Some biological characteristics of the ectoparasitoid Dineulophus phtorimaeae (de Santis) (Hymenoptera: Eulophidae) and field interaction with the endoparasitoid Pseudapanteles dignus (Muesebeck), both larval parasitoids of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), were examined. In addition, we completed the original description of D. phtorimaeae. Preimaginal developmental time of the ectoparasitoid was 11.17 ± 0.60 d for both sexes, and adult life span was 11.73 ± 0.92 d for females and 8.78 ± 0.93 d for males. The proportion of males to females was equal. In the field, hosts were parasitized at the third larval instar. On average, a female attacked ca. four hosts throughout her lifetime and deposited eggs in ≈50% of cases. The most successful female attacked six hosts, yielding a potential fecundity of ≈10 eggs. Host paralysis without parasitism was observed, suggesting stinging for host feeding. The daily oviposition curve is compatible with a synovigenic-type parasitoid. Our prediction stating that D. phtorimaeae would succeed when competing for hosts with P. dignus was correct, because the former species had greater parasitism rates. In the field, both T. absoluta parasitoids were able to coexist at leaf scale. The negative aspects of differences in feeding behavior, narrower host range (third instar), and lower fecundity of D. phtorimaeae would be compensated by its better attributes as natural enemy, in comparison with P. dignus, enabling coexistence.

Short and long-term effects of three neurotoxic insecticides on biological and behavioural attributes of the orb-web spider Alpaida veniliae (Araneae, Araneidae): implications for IPM programs

Soybean pest control in Argentina is done just by chemical control using broad-spectrum pesticides. Alpaida veniliae (Araneae, Araneidae) is one of the most abundant spider species of the orb web weaver guild in soybean, and it is considered a very important polyphagous predator, attacking different insects’ families. The objective of this study was to determine if neurotoxic insecticides commonly used in soybean crops and a new active ingredient registered in Argentina (spinosad) adversely affected survival, prey consumption, mating behaviour, web building and reproductive capacity of A. veniliae females, under standard laboratory conditions. Spinosad was the most harmful insecticide due to high acute toxicity, even at lower concentrations than those registered for its field use and for its sublethal effects also. Cypermethrin caused several sublethal effects although its acute toxicity on spider was lower than other insecticides. It reduced prey consumption, affected web building, caused abnormalities in eggs sacs and decreased drastically the fecundity and fertility at sublethal concentrations. Endosulfan did not reduce prey consumption but it affected web building, caused abnormalities in eggs sacs and egg masses, and decreased the fecundity and fertility. Spinosad was also the compound with the most drastic effect on web building, it did not reduce prey consumption and fecundity, but fertility was reduced and abnormalities in egg sacs and egg masses were observed. The use of these insecticides in IPM programs according to their potential toxicity on spider communities is discussed.

Parasitoid assemblages of soybean defoliator Lepidoptera in north‐western Buenos Aires province, Argentina

1 The objective of this study was to examine the structure of parasitoid assemblages attacking soybean defoliator Lepidoptera in north‐western Buenos Aires province, Argentina.

Pest management plan for the two-spotted spider mite, Tetranychus urticae, based on the natural occurrence of the predatory mite Neoseiulus californicus in strawberries

We developed and validated a management plan for Tetranychus urticae in strawberries, based on the natural control exerted by Neoseiulus californicus and on acaricide applications made only when necessary. The plan has two components: a sampling protocol and a decision chart. Systematic presence–absence sampling of active T. urticae and N. californicus was used to predict prey and predator densities relying only on the proportion of T. urticae-infested leaflets, once the occurrence of the predator was detected in at least one of them. The decision chart, which was constructed taking into account the pest and predator densities and the pests rate of increase, determines the range in the proportion of T. urticae-infested leaflets that will require different actions: to use selective acaricides and re-check at 7 days, to take no action but re-check at 7 days, or to take no action but re-check at 14 days. The management plan was potentially effective and feasible, showing that natural populations of N. californicus can consistently exert strong top-down suppression of T. urticae. Thus, N. californicus is a promising candidate for conservation biological control.