Toxicity and Lethal Effect of Greenhouse Insecticides on Coccinella septempunctata (Coleoptera: Coccinellidae) as Biological Control Agent of Myzus persicae (Hemiptera: Aphididae).

Deltamethrin and imidacloprid are commonly used insecticides for controlling sub-sucking insects in greenhouses. However, their application may cause sublethal effects on the aphid coccinellid predator Coccinella septempunctata (Coleoptera: Coccinellidae). Here, we study (i) the toxicity and the effect of two sublethal doses (LD10 and LD30) of deltamethrin and imidacloprid on C. septempunctata in a laboratory microcosm and (ii) the residual toxicity of the two insecticides in a greenhouse. The results showed that both insecticides reduced fecundity, longevity, the intrinsic rate of increase, the finite rate of increase and the net reproductive rate. However, the developmental time of the fourth instar larvae was prolonged by both insecticides at LD10 and LD30. Deltamethrin residues were toxic 21 DAT (days after treatment) to C. septempunctata fourth instar larvae. In contrast, imidacloprid began in the slightly harmful category (75%) 1 DAT and declined to the harmless category (18.33%) 21 DAT. These results indicate that deltamethrin and imidacloprid have potential risks to C. septempunctata. This study provides information to guide the development of integrated pest management (IPM) strategies in greenhouses.

Toxicity and Influence of Sublethal Exposure to Sulfoxaflor on the Aphidophagous Predator Hippodamia variegata (Coleoptera: Coccinellidae).

Hippodamia variegata (Goeze), the variegated ladybug, is a predator of many insect pests, especially aphids. Sulfoxaflor is a chemical insecticide that can be used to control many sap-feeding insect pests, for instance, plant bugs and aphids, as an alternative to neonicotinoids in different crops. To improve the combination of the H. variegata and sulfoxaflor in an IPM (integrated pest management) program, we studied the ecological toxicity of the insecticide to the coccinellid predator at sublethal and lethal doses. We examined the influence of sulfoxaflor on larvae of H. variegata using exposure doses of 3, 6, 12, 24, 48 (maximum recommended field rate (MRFR)), and 96 ng a.i. per insect. In a 15-day toxicity test, we observed decreased adult emergence percentage and survival, as well as an increased hazard quotient. The LD50 (dose causing 50% mortality) of H. variegata due to sulfoxaflor decreased from 97.03 to 35.97 ng a.i. per insect. The total effect assessment indicated that sulfoxaflor could be grouped as slightly harmful for H. variegata. Additionally, most of the life table parameters were significantly decreased after exposure to sulfoxaflor. Overall, the results present a negative influence of sulfoxaflor on H. variegata when applied at the recommended field dose for controlling aphids in Greece, which demonstrates that this insecticide may only be employed with care when used in IPM programs.

Mortality of four stored product pests in stored wheat when exposed to doses of three entomopathogenic nematodes.

The insecticidal effect of Heterorhabditis bacteriophora Poinar (Nematoda: Heterorhabditidae), Steinernema carpocapsae (Weiser) (Nematoda: Steinernematidae), and Steinernema feltiae (Filipjev) (Nematoda: Steinernematidae) against Mediterranean flour moth, Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) (larvae), lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) (adults), rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) (adults), and confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) (adults and larvae) was examined under laboratory conditions in wheat, Triticum aestivum L. The nematodes were applied at the following doses: 0 (control), 100, 500, 1,000, 1,500, 5,000, 10,000, and 20,000 infective juveniles (IJs) per ml, corresponding to 10, 50, 100, 150, 500, 1,000, and 2,000 IJs per insect, and their infectivity was tested at 20 and 30 degrees C after 4 and 8 d of exposure. For E. kuehniella larvae wheat treatments with S. feltiae provided mortality that ranged from 36.7 to 78.3% whereas no mortality was noted in the treatment with S. carpocapsae at 100 IJs per ml at 20 or at 30 degrees C. Also, at 20 degrees C, in wheat treated with H. bacteriophora at 100 IJs per ml, very few larvae were dead. For R. dominica adults, at 20 degrees C, the mortality of adults in wheat treated with S. feltiae and S. carpocapsae did not exceed 23.3 and 41.7%, respectively, at 20,000 IJs per ml, with no significant differences among doses. In the case of S. oryzae adults, the mortality was very low at all doses, and temperatures and did not exceed 9%. Mortality of T. confusum adults did not exceed 17% regardless of the entomopathogenic nematode species tested. In contrast, mortality of T. confusum larvae was notably higher and exceeded 56% in wheat treated with 10,000 or 20,000 IJs per ml of S. feltiae at 20 degrees C. Unlike S. feltiae and S. carpocapsae, the application of H. bacteriophora resulted in lower mortality levels. Generally, the increase of temperature reduced the mortality levels of the T. confusum larvae. In most cases, the efficacy level of the tested entomopathogenic nematode species increased with the dose and decreased with the increase of temperature.

Resistance of transgenic tobacco plants incorporating the putative 57-kDa polymerase read-through gene of Tobacco rattle virus against rub-inoculated and nematode-transmitted virus.

Nicotiana tabacum plants were transformed with the 57-kDa read-through domain of the replicase gene of Tobacco rattle virus (TRV) isolate SYM. From a total of six lines containing the viral transgene, four displayed various levels of resistance to TRV infection. Transgenic plants from line 81G were highly resistant to foliar rub-inoculation with the homologous isolate, or with isolates TRV-PpK20 and TRV-PLB, which are almost identical to TRV-SYM in RNA1 sequence. Moreover, 81G plants were moderately resistant to the serologically and genetically distinct, highly pathogenic isolate TRV-GR. Resistance characteristics of line 81G remained stable over six generations. No unambiguous correlation was established between number of transgene insertion loci and level of resistance. Transgene-specific mRNA was clearly detected in plants from susceptible lines but only at an early developmental stage in resistant plants, indicating the operation of a RNA silencing resistance mechanism. Following challenge using viruliferous vector nematodes carrying TRV-PpK20 or by rub inoculation of roots, 81G plants did not show any symptoms and virus was not detected in leaves. However, virus was detected in roots but without apparent effects on plant growth and often at low concentration. When challenged with nematodes carrying TRV-GR, symptoms in aerial parts of 81G plants were less severe and much delayed compared to non-transgenic plants, although younger plants showed less resistance than older ones. No difference was detected in transgene transcript accumulation between leaves and roots of 81G plants. This is the first work reporting a broad level of pathogen derived resistance against two geographically and genetically distinct TRV isolates transmitted directly by their nematode vectors and provides further insight into the expression of transgenic resistance against naturally transmitted soil-borne viruses.

Review of the ultrastructure of the nematode body cuticle and its phylogenetic interpretation.

The phylogenetic interpretation of the nematode cuticle ultrastructure is reviewed within the framework of recent DNA-sequence data. In particular, the structure of the median and basal zones is discussed. Several structural elements of the cuticle seem to have arisen independently several times within the Nematoda and thus are highly homoplasious (e.g. the cortical or basal radial striae, spiral fibre layers and a fluid matrix with struts). Moreover, identifying the homology of the nematode cuticle ultrastructures is often very difficult at deep taxonomic levels. Hence, the cuticle appears to be unreliable regarding resolution of deep-level relationships in the Nematoda. However, at less inclusive taxonomic levels (e.g. families, genera, ...) the cuticle seems to be a more reliable phylogenetic marker.