Summary The plant availability of phosphate applied to calcareous soils is affected by precipitation and adsorption reactions, the relative significance of which is not well known. We used extended P‐sorption curves obtained at phosphate addition rates up to 340 mmol P kg−1 soil to examine the relative contribution of precipitation and adsorption by 24 calcareous Spanish Vertisols and Inceptisols. Adsorption was dominant at 1 day and at small rates of addition (10–35 mmol P kg−1). With increasing clay and Fe and Al oxides contents of the soil, more phosphate was sorbed before the sorption curve bent upwards, as a result of Ca phosphate precipitation. Sorption curves showed a nearly vertical intermediate region, the length of which increased with time, suggesting that a Ca phosphate buffered the concentration of P in solution. The buffering concentration decreased with time, suggesting a progressive transformation of more to less soluble forms of Ca phosphate. A phase less soluble than octacalcium phosphate seemed to control the concentration of P in solution at 180 days in most soils. The apparent solubility of this phase decreased with increasing carbonate content in the soil. Precipitation of poorly soluble Ca phosphates apparently predominated up to a P addition dose ranging from about 30 mmol P kg−1 in some soils to more than 340 mmol P kg−1 in others. At larger doses, the way additional P was bound to the solid phase was different; phosphate was probably adsorbed, at least in part, to low‐affinity sites on silicate clays and oxides. The proportion of sorbed phosphate that was isotopically exchangeable decreased with time, soil carbonate content and P addition dose for doses <100 mmol P kg−1. This is consistent with the idea that P in Ca phosphates is less isotopically exchangeable than P adsorbed on mineral surfaces. At larger additions of P, isotopic exchangeability was unrelated to the soil properties measured, probably because there was a variety of sorbed P forms influenced in turn by different soil components.

Podisus nigrispinus Dallas (Heteroptera: Pentatomidae), released in biological control programs, is a predator of Lepidopteran and Coleopteran species. Lemongrass essential oil and its constituents can be toxic to this natural enemy. The major constituents of lemongrass essential oil are neral (31.5%), citral (26.1%), and geranyl acetate (2.27%). Six concentrations of lemongrass essential oil and of its citral and geranyl acetate constituents were applied to the thorax of P . nigrispinus nymphs and adults. The walking and respiratory behavior of the P . nigrispinus third-instar nymphs, treated with citral and geranyl acetate at the LD 50 and LD 90 doses, were analyzed with video and respirometer. The lemongrass essential oil toxicity increased from first- to fifth-instar P . nigrispinus nymphs. The P . nigrispinus respiration rates (μL de CO 2 h −1 /insect) with citral and geranyl acetate in the LD 50 and LD 90 differed. Nymphs exposed to the lemongrass essential oil and its constituents on treated surfaces presented irritability or were repelled. Podisus nigrispinus adults were tolerant to the lemongrass essential oil and its constituents, geranyl acetate and citral. The altered respiratory activity with geranyl acetate and the fact that they were irritated and repelled by citral suggest caution with regard to the use of the lemongrass essential oil and its constituents in integrated pest management incorporating this predator, in order to avoid diminishing its efficiency against the pests.

Entomopathogenic nematodes (EPNs) (Steinernematidae and Heterorhabditidae) can control pests due to the mutualistic association with bacteria that kill the host by septicemia and make the environment favorable for EPNs development and reproduction. The diversity of EPNs in Brazilian soils requires further study. The identification of EPNs, adapted to environmental and climatic conditions of cultivated areas is important for sustainable pest suppression in integrated management programs in agricultural areas of Brazil. The objective was to identify EPNs isolated from agricultural soils with annual, fruit and forest crops in Brazil. Soil samples were collected and stored in 250 ml glass vials. The nematodes were isolated from these samples with live bait traps ([Galleria mellonella L. (Lepidoptera: Pyralidae) larvae]. Infective juveniles were collected with White traps and identified by DNA barcoding procedures by sequencing the D2/D3 expansion of the 28S rDNA region by PCR. EPNs identified in agricultural areas in Brazil were Heterorhabditis amazonensis, Metarhabditis rainai, Oscheios tipulae and Steinernema rarum. These species should be considered pest biocontrol agents in Brazilian agricultural areas.

No abstract

Thaumastocoris peregrinus Carpintero and Dellape (Hemiptera: Thaumastocoridae) is a sap-sucking insect that has become a major pest of eucalypts. The entomopathogenic fungi Beauveria bassiana (Bals.-Criv.) Vuill. and Metarhizium anisopliae (Metsch.) Sorokin have the potential to control insect pests. This study evaluated the susceptibility of T. peregrinus to two commercial products based on conidia of B. bassiana and M. anisopliae. The fungi were sprayed onto adults of T. peregrinus at a concentration of 1 × 10 8 conidia mL −1 to evaluate their pathogenicity and conidial production on the insect cadavers. Beauveria bassiana caused 100 % mortality, while M. anisopliae caused more than 80 % mortality of T. peregrinus adults 11 days after fungi application. The fungi colonized the head and thorax regions and caused high mortality rates through conidial production. Pathogenicity of entomopathogenic fungi B. bassiana and M. anisopliae to T. peregrinus show potential to use these fungi in integrated pest management.

Bioinsecticides and transgenic plants, based on Bacillus thuringiensis (Bt) toxins are important when managing Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae), a soybean defoliator pest. The interaction of these toxins with the caterpillar’s midgut cells determines their efficacy as an insecticide. The objective was to evaluate the toxicity of B. thuringiensis , subsp . kurstaki strain HD-1 and cytopathological changes mediated by these bacterial toxins in the midgut of A. gemmatalis caterpillars. Insecticidal efficacy was determined by calculating lethal concentration values (LC 25 , LC 50 , LC 75 , LC 90 and LC 99 ) in the laboratory. Midgut fragments from A. gemmatalis were extracted after bacterial ingestion and evaluated by light, transmission electron and confocal microscopy. The Bt median lethal concentrations showed toxicity [LC 50 = 0.46 (0.43–0.49) mg mL −1 ] to fourth instar A. gemmatalis caterpillars after 108 hours. Bt induces severe cytotoxicity to A. gemmatalis midgut epithelial cells with increasing exposure over time, causing cellular disorganization, microvillus degeneration, cell fragmentation and protrusion, peritrophic membrane rupture, and cell vacuolization. The cell nuclei presented condensed chromatin and an increase in lysosome numbers. Apoptosis occurred in the midgut cells of caterpillars exposed to Bt. A regenerative response in A. gemmatalis caterpillars was observed 8 hours after exposure to Bt, however this response was not continuous. Toxins produced by Bt are harmful to A. gemmatalis at median concentration with structural damage and death of the midgut epithelial cells of this insect.

Efficient strategies to control the bronze bug Thaumastocoris peregrinus Carpintero and Dellapé (Hemiptera: Thaumastocoridae) are unavailable, but Cleruchoides noackae Lin and Huber (Hymenoptera: Mymaridae) parasitizes eggs of this pest. The parasitism and number of parasitoids that emerged from the eggs of T. peregrinus were evaluated in the laboratory and from eggs of this pest collected in the field in an area of approximately 2 ha. Collections were done 1 yr after the first release of C. noackae to check for field establishment of this parasitoid in eucalyptus plantations in Minas Gerais State, Brazil. The emergence of C. noackae was 53 and 52% from eggs parasitized in the laboratory and in the field, respectively. This natural enemy was recorded for all sampling points from the field collections, which were up to 10 km from the place it had been released. The C. noackae establishment in the field, and the potential for biological control of T. peregrinus by this parasitoid were confirmed.

No abstract