Luísa Oliveira

Effects of Conventional Pesticides on the Preimaginal Developmental Stages and on Adults of Trichogramma cordubensis (Hymenoptera: Trichogrammatidae)

The effects of seven pesticides sprayed on hosts with parasitoids at different phases of egg to adult development (24, 24-48, 48-72, 72-96, 120-144, 192-216 h) of Trichogramma cordubensis (Vargas & Cabello) were studied. The effect of these pesticides on the mortality of adult parasitoids upon contact with the hosts immediately or 24 h after the treatments was also tested. One organophosphate insecticide (trichlorfon), one organochlorine insecticide (endosulfan), two pyrethroids (deltamethrin and lambda-cyhalothrin), a commercial formulation of Bacillus thuringiensis subsp. Kurstaki , and two fungicides (acetamide + dithiocarbamete and basic copper sulphate) were selected for testing. All the tests were carried out with fresh solutions of commercial insecticides applied on host eggs at the recommended concentration. The pesticides applied at different development phases did not affect the duration of parasitoid development, except endosulfan, which delayed the parasitoid preimaginal development for one day. With few exceptions, the number of parasitized host eggs that turned black (i.e. with parasitoid prepupae) did not differ significantly between the pesticide treatments and the control. The chemical insecticides affected the adult emergence rates significantly, while the other products resulted in emergence rates similar to control values. The longevity of adult progeny was very short when endosulfan or trichlorfon (<1 and <2 days, respectively) were applied. Overall, endosulfan was the pesticide most harmful to the preimaginal development stages of T. cordubensis . Therefore, the use of this product should be avoided when this species is part of an integrated pest control programme.

Biological activity of essential oils from seven Azorean plants against Pseudaletia unipuncta (Lepidoptera: Noctuidae)

Ten essential oils from seven Azorean plant species were evaluated for their insecticidal, ovicidal, feeding‐deterrence and growth inhibition activities against Pseudaletia unipuncta. The oils of Laurus azorica (leaves), and Juniperus brevifolia (leaves) showed strong moderate insecticidal effect on fourth‐instar larvae causing 93.3% and 46.7% mortality, respectively. Juniperus brevifolia (leaves), L. azorica (leaves), Persea indica (leaves), Hedychium gardnerianum (leaves) and Pittosporum undulatum (fruits and leaves) significantly affected the hatching of P. unipuncta eggs (<8% eclosions). Five oils showed significant feeding deterrent activities (L. azorica, 92.4%, J. brevifolia, 93.6%, P. undulatum leaves, 95.5% and fruits, 83.8% and H. gardnerianum, 88.2%). All of the essential oils tested, significantly inhibited the larval growth after 5u2003days of feeding on the treated diet. Essential oils from L. azorica and J. brevifolia were the most potent growth inhibitors among the oils tested, producing a decrease in the initial larva weight (−14.8 and −14.5u2003mg, respectively). Our results indicate that L. azorica (leaves), J. brevifolia (leaves), P. indica (leaves), H. gardnerianum (leaves), and P. undulatum (leaves and fruits) can be exploited for the development of bioactive compounds as a new source of agrochemicals. Further emphasis on isolation and identification of active constituents can be useful to develop new environment‐friendly insect control agents.

Activities of Apiaceae Essential Oils against Armyworm, Pseudaletia unipuncta (Lepidoptera: Noctuidae)

Essential oils (EOs) from four Apiaceae species and 11 pure compounds were evaluated for their antifeedant, growth inhibitory, and insecticidal activities against Pseudaletia unipuncta (Lepidoptera: Noctuidae) fourth-instar larvae. EOs from Foeniculum vulgare subsp. vulgare var. vulgare, Anethum graveolens , Petroselinum crispum , and Cuminum cyminum were characterized by gas-chromatography (GC) and mass spectrometry. Anti-insect activity varied according to plant specie/composition, type, and exposure period. EOs from P. crispum and A. graveolens fruits, trans-anethole and cuminaldehyde, exerted acute effects on larvae feeding and growth (FDI and GI > 70%). A. graveolens , C. cyminum , and F. vulgare EOs and some of their constituents were effective by fumigation (≥ 80%). Satisfactory contact toxicities (>70%) were observed for five compounds and all EOs, except F. vulgare EOs, when tested by the filter paper impregnation method. For the most active EOs/compounds, dose-dependent toxicity was determined and inverse relationships of LC50 with time were established.

High-performance liquid chromatography-diode array detection-electrospray ionization multi-stage mass spectrometric screening of an insect/plant system: the case of Spodoptera littoralis/Lycopersicon esculentum phenolics and alkaloids.

High-performance liquid chromatography-diode array detection-electrospray ionization multi-stage mass spectrometry (HPLC-DAD-ESI-MS(n)) is considered to be a very valuable tool for the characterization of compounds found in trace amounts in natural matrices, as their previous isolation and clean-up steps can be avoided. Micro-scale separation increases the potential of this analytical technique, allowing the determination of compounds in reduced samples. Spodoptera littoralis represents a major challenge to Solanaceae plants, as it is one of the most deleterious pests. The S. littoralis/Lycopersicon esculentum system was studied for the first time concerning glycoalkaloids and phenolics. Using HPLC-DAD-ESI-MS(n) we were able to characterize 15 phenolic compounds in L. esculentum leaves. Nine of them are reported for the first time. Some differences were found between leaves of cerasiforme and Bulls heart varieties. However, in the materials of S. littoralis (larvae, adults, exuviae and excrements) reared in both L. esculentum leaves no phenolics were identified. α-Tomatine was the main glycoalkaloid in the host plant. The glycoalkaloid composition of the different S. littoralis materials was distinct, with α-tomatine and dehydrotomatine being the main detected compounds in larvae and excrements. These results add knowledge to the ecological interaction in this insect/plant duo, for which it is hard to obtain considerable sample amounts.

Fast determination of bioactive compounds from Lycopersicon esculentum Mill. leaves.

Lycopersicon esculentum leaves, usually considered as a by-product of tomato production, present several bioactive compounds of interest for industries like food, pharmaceutical and cosmetics. Nevertheless, before industrial application, suitable methods to identify and quantify those metabolites should be developed. In this study agitation with aqueous methanol was used for phenolic compounds extraction. Solid-phase extraction (SPE) was performed as the purification step before alkaloids analysis. Among the SPE sorbents tested, sulphonic acid bonded silica with H(+) counterion (SCX) proved to be the most efficient one for removing interfering components. Fifteen phenolics and four steroidic alkaloids were identified in 35 and 20 min analysis, respectively. The optimised methods were validated, revealing to be accurate, fast, simple and sensitive. Thus, these methods represent an easy and fast analytical approach, using equipment available in almost laboratory, which render them to be appropriate for routine analysis.

Side-effects of organic and synthetic pesticides on cold-stored diapausing prepupae of Trichogramma cordubensis

The side-effects of three insecticides (deltamethrin, lambda-cyhalothrin and Bacillus thuringiensis Berliner) and one fungicide (basic copper sulphate) were tested on cold-stored diapausing prepupae of Trichogramma cordubensis Vargas and Cabello (Hymenoptera: Trichogrammatidae). Pesticides were directly sprayed on parasitized host eggs (being the diapausing parasitoids in the prepupal stage) after cold storage (3°C) for three different periods (60, 120 and 180xa0days). Regardless of the period of cold storage, both pyrethroids reduced the emergence rates of T. cordubensis (both <25%) compared to the control (emergence varied from 83% to 89%). The most toxic pyrethroid was lambda-cyhalothrin; Trichogramma cordubensis adult emergence varied from 7% to 15%. Lambda-cyhalothrin also negatively affected the longevity and fecundity of parasitoids cold stored for 60xa0days. Bacillus thuringiensis Berliner subsp. kurstaki and basic copper sulphate had little or no adverse effect on emergence rates (generally >80%), longevity nor fecundity of T.xa0cordubensis, indicating that these pesticides could be successfully integrated into pest management programs using wasps that were cold stored under diapause. Such integration would be valuable to pest management programs by reducing the costs of T.xa0cordubensis mass rearing and by allowing producers to stockpile parasitoids for release in the growing season. However, since the emergence rate, longevity and fecundity of T.xa0cordubensis generally decreased with increasing duration in cold storage, wasps to be used in integrated pest management programs should only be stored at 3°C for 60xa0days maximum.

Larval Mortality Factors of Spodoptera Littoralis in the Azores

Mortality among larval developmental stages of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), was determined by weekly sampling on weeds in a pasture on São Miguel Island (Azores, Portugal), from August to December, over a 3-year period (1999–2001). In all the years surveyed, larvae of S. littoralis usually appeared in pastures after the third week of August, with higher abundances in September and the beginning of October. Three different factors causing larval mortality were identified: one fungal pathogen, Furia virescens (Thaxter) Humber (Zygomycetes: Entomophthoraceae), two nucleopolyhedroviruses and one larval parasitoid, Meteorus communis (Cresson) (Hymenoptera: Braconidae). The percentages of dead larvae infected by virus or fungus were significantly higher than the other causes of mortality, regardless of the year. Furthermore, the percentage of larvae that died due to virus contamination was generally higher than the percentage of larvae infected by fungus. Significant correlations between the environmental factors and the percentage of larvae infected by virus or by fungus, were only observed during 2001. In 2001, the prevalence of fungal infection was negatively correlated with that of viral infection although prevalences of these two agents were positively correlated in both 1999 and 2000. These results show that virus and fungus are potential biological control agents for S. littoralis in Azores.

Effects of the larval diet of Pseudaletia unipuncta (Lepidoptera: Noctuidae) on the performance of the parasitoid Glyptapanteles militaris (Hymenoptera: Braconidae).

Abstract We evaluated preferences of the parasitoid Glyptapanteles militaris (Walsh) among various host-diet complexes in an effort to understand the abundance of the parasitoid in Azorean pastures. We also examined effects of host diet on the quality of the parasitoid as a biological control agent. The larvae of Pseudaletia unipuncta (Haworth) were reared on three different diets (Zea mays L., Lolium perenne L., and artificial diet) and were exposed to G. militaris. The percentage of parasitized larvae (yielding parasitoid cocoons), of host mortality unrelated to successful parasitism (host death without cocoon formation) and of pupating hosts did not differ significantly among diet treatments. Also, the total number of parasitoid larvae per host and the mean number of cocoons yielded per host did not differ significantly when hosts were fed on different diets. Time from egg to cocoon formation (16.1 and 18.6 d, respectively), pupal period (8.0 and 8.5 d, respectively), and total developmental time (24.1 and 26.9 d, respectively) for G. militaris were significantly shorter (at 22°C) when hosts were reared on L. perenne compared with artificial diet. Rate of adult parasitoid emergence from cocoons was significantly lower when hosts were fed artificial diet (82.5%) than when fed L. perenne (91.2%) or Z. mays (91.1%). The longevity of the adults of G. militaris ranged from 5.1 to 7.2 d among treatments differed significantly for the three types of diets and between sexes. When adults of G. militaris could choose among hosts reared on Z. mays, L. perenne, or artificial diet, they preferred the hosts fed L. perenne leaves. These results suggest that the parasitoid may be well adapted to the Azorean agricultural ecosystems, characterized by the prevalence of L. perenne throughout the year. Results show that hosts fed fresh leaves of L. perenne are the most suitable for the mass rearing of G. militaris.

Effects of deltamethrin on the reproduction of Trichogramma cordubensis (Hymenoptera: Trichogrammatidae)

Abstract The influence of deltamethrin on the reproduction of Trichogramma cordubensis, a thelytokous egg parasitoid, was investigated by studying egg maturation and daily fecundity of insecticide treated wasps and offspring emergence rates. The insecticide was applied to the parasitoids at the prepupal stage within its host eggs (Ephestia kuehniella). The total number of parasitized eggs per female during the first 7 days was not significantly influenced by the tested concentrations of deltamethrin. Prevalence of parasitism during this period had a similar pattern between deltamethrin treatments and the control. In addition, the mean number of mature eggs observed per female per day was significantly correlated to mean daily fecundity, regardless of the treatments. Offspring emergence was significantly influenced by the insecticide treatments experienced on their progenitors, decreasing significantly at 48 and 72 h for the highest tested concentration of deltamethrin (23.6 mg [a.i.]/L). Despite that, deltamethrin had no adverse effects on the reproduction of treated wasps, particularly when was applied at the concentration recommended by the manufacturer (12.5 mg [a.i.]/L).

Susceptibility to insecticides of Glyptapanteles militaris (Hymenoptera: Braconidae), a Parasitoid of Pseudaletia unipuncta (Lepidoptera: Noctuidae)

The susceptibility of cocoons and adults of Glyptapanteles militaris (Walsh) were studied. One organophosphate insecticide (trichlorfon), one organochlorine insecticide (endosulfan), one pyrethroid (deltamethrin) and a commercial formulation of Bacillus thuringiensis subsp. Kurstaki were selected for testing. All the tests were carried out with fresh solutions of commercial insecticides applied on host larvae at the recommended concentration. One- and 6-day-old cocoons were sprayed with the insecticide solutions by means of a Potter Tower and held for adult emergence. Adults were exposed to residues of insecticides inside plastic vials. The B. thuringiensis formulation had no harmful effect on the cocoons nor on the adults. Trichlorfon and endosulfan were highly toxic to all the tested stages. Deltamethrin was highly toxic to adults but relatively safe when applied on parasitoid cocoons. Based on these results, field applications of deltamethrin would be least disruptive of tested insecticides to populations of G. militaris.