Johan Desaeger

Identification of a critical region in the Drosophila ryanodine receptor that confers sensitivity to diamide insecticides.

Anthranilic diamides, which include the new commercial insecticide, chlorantraniliprole, are an exciting new class of chemistry that target insect ryanodine receptors. These receptors regulate release of stored intracellular calcium and play a critical role in muscle contraction. As with insects, nematodes express ryanodine receptors and are sensitive to the plant alkaloid, ryanodine. However the plant parasitic nematode, Meloidogyne incognita, is insensitive to anthranilic diamides. Expression of a full-length Drosophila melanogaster ryanodine receptor in an insect cell line confers sensitivity to the receptor agents, caffeine and ryanodine along with nanomolar sensitivity to anthranilic diamides. Replacement of a 46 amino acid segment in a highly divergent region of the Drosophila C-terminus with that from Meloidogyne results in a functional RyR which lack sensitivity to diamide insecticides. These findings indicate that this region is critical to diamide sensitivity in insect ryanodine receptors. Furthermore, this region may contribute to our understanding of the differential selectivity diamides exhibit for insect over mammalian ryanodine receptors.

Effect of application timing and method on efficacy and phytotoxicity of 1,3‐D, chloropicrin and metam‐sodium combinations in squash plasticulture

BACKGROUND Metam-sodium, 1,3-dichloropropene (1,3-D) and chloropicrin are widely used soil fumigants. Combined application of metam-sodium and 1,3-D + chloropicrin is intended to improve efficacy and broaden spectrum of control, but little is known about the effect on crop safety. This study aimed to evaluate the effects of application timing of fumigant combinations on soilborne pest and disease control (nematodes, soil fungi and weeds) and growth of squash. Two separate tests with chisel-injected and drip-applied fumigant combinations and plant-back times ranging from 1 to 4 weeks were conducted in Tifton, GA, USA, in spring and fall 2002. RESULTS Fumigant combinations using 1,3-D, chloropicrin and metam-sodium were as effective as methyl bromide in controlling Meloidogyne incognita (Kofoid & White) Chitwood, Pythium irregulare Buis., Rhizoctonia solani Kühn and Cyperus esculentus L. Chisel-applied combinations were more effective in terms of root-knot nematode control than drip-applied combinations. Root-knot nematode reduced squash yields by up to 60%. Phytotoxicity problems and lower yields were observed during spring, especially following 1,3-D + chloropicrin and when plant-back periods were shorter. CONCLUSION The main problem with fumigant alternatives to methyl bromide may not be reduced efficacy but, in particular for 1,3-D products, loss of flexibility in terms of longer plant-back periods.

Effect of methomyl and oxamyl soil applications on early control of nematodes and insects

BACKGROUND Methomyl is a widely used carbamate insecticide that has traditionally been applied as a foliar spray. More recently, methomyl has been labeled as a soil application via drip chemigation. Not much is known about the insecticidal and nematicidal potential of soil-applied methomyl. Methomyl soil applications were evaluated for their potential to control soil nematodes and foliar insect pests in a series of lab and greenhouse tests. RESULTS Methomyl showed rapid knockdown of Meloidogyne incognita (Kof. & White) Chitwood in aqueous assays, with EC50 and EC90 values that were similar to oxamyl and averaged 4.9 and 15.2 mg L(−1). In the greenhouse, soil applications of methomyl ranging from 0.56 to 4.0 kg ha(−1) provided significant M. incognita control similar to oxamyl during early growth (up to 25 days after planting) of pea and bean. Higher application rates and split applications improved nematode control, but also increased the risk of phytotoxicity. Methomyl soil applications were highly effective on several insects including Myzus persicae (Sulzer), Aphis gossypii (Glover), Frankliniella occidentalis Perg. and Spodoptera exigua (Hübner). Methomyl was about 5–9-fold more potent on M. persicae and A. gossypii when applied via soil drench as opposed to foliar spray. Potency on Bemisia tabaci Genn., S. exigua and Trichoplusia ni Hübner was about the same with the two application methods. CONCLUSION Methomyl soil applications showed good potential for early control of various insect and nematode pests. Further testing is required to verify activity under field conditions.

The discovery of fluazaindolizine: A new product for the control of plant parasitic nematodes

Fluazaindolizine is a new highly effective and selective product for the control of plant parasitic nematodes. Specificity for nematodes coupled with absence of activity against the target sites of commercial nematicides suggests that fluazaindolizine has a novel mode of action. The discovery, structure-activity development and biological properties for this new class of nematicides are presented.