Can the botanical azadirachtin replace phased-out soil insecticides in suppressing the soil insect pest Diabrotica virgifera virgifera?

Abstract

Background Due to recent bans on the use of several soil insecticides and insecticidal seed coatings, soil-dwelling insect pests are increasingly difficult to manage. One example is the western corn rootworm (Diabrotica virgifera virgifera, Coleoptera: Chrysomelidae), a serious root-feeder of maize (Zea mays). We investigated whether the less problematic botanical azadirachtin, widely used against above-ground insects, could become an option for the control of this soil insect pest. Methods Artificial diet-based bioassays were implemented under standard laboratory conditions to establish dose response curves for the pest larvae. Then, potted-plant experiments were implemented in greenhouse to assess feasibility and efficacy of a novel granular formulation of azadirachtin under more natural conditions and in relation to standard insecticides. Results Bioassays in three repetitions revealed a 3-day LD50 of 22.3 µg azadirachtin/ml which corresponded to 0.45 µg/neonate of D. v. virgifera and a 5-day LD50 of 19.3 µg/ml or 0.39 µg/first to second instar larva. No sublethal effects were observed. The three greenhouse experiments revealed that the currently proposed standard dose of a granular formulation of 38 g azadirachtin/hectare for in-furrow application at sowing is not enough to control D. v. virgifera or to prevent root damage. At 10× standard-dose total pest control was achieved as well as the prevention of most root damage. This was better than the efficacy achieved by cypermethrin-based granules and comparable to tefluthrin-granules, or thiamethoxam seed coatings. The ED50 for suppressing larval populations were estimated at 92 g azadirachtin/ha, for preventing heavy root damage 52 g/ha and for preventing general root damage 220 g/ha. Conclusions There seems clear potential for the development of neem-based botanical soil insecticides for arable crops such as maize. They might become, if doses are increased and more soil insecticides phased out, a promising, safer solution as part of the integrated pest management toolkit against soil insects.

Evaluating the Toxicity of Piperine, Azadirachtin, and Quercetin against Solenopsis invicta Buren (Hymenoptera: Formicidae) Workers via Feeding Bioassay under Controlled Condition

“…Previous researches also reported azadirachtin as repellent and toxic against large spectrum of insect pests. In an experiment, azadirachtin effectively protected maize crop against western corn root worm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) (Toepfer et al, 2021). Azadirachtin also induces serious behavioral changes in Drosophila melanogaster and can be manipulated in management strategies against this insect pest (Bezzar- Bendjazia et al, 2017).…”

Limited Influence of Abiotic and Biotic Factors on the Efficacy of Soil Insecticides and Entomopathogenic Nematodes when Managing the Maize Pest Diabrotica v. virgifera (Coleoptera: Chrysomelidae)

“…Experiments were implemented following the EPPO standards PP 1/212 and PP 1/152 [57,58]. Four or five plots of four to six rows of maize were systematically arranged per treatment and control (Table S1).…”

“…Weekly emergence data of adults were standardized to 100 eggs per plant. The efficacy of each treatment was calculated as the reduced emergence of beetles relative to the emergence of beetles from untreated control (corrected efficacy % = 100 × (beetles in control plots-beetles in treated plots)/maximum (beetles in the control or treated plots) [calculation according to [58]].…”

Sustainable intensification of smallholder farming systems in Sub-Saharan Africa and South Asia

“…There is renewed interest in the use of pesticidal plants along with soil health improvement to better manage insect pests and diseases (Belmain et al, 2022). Common bean smallholder farmers in our study area use pesticidal plants for controlling insect pests and diseases, mainly targeting above-ground pests and diseases (Mkindi et al, 2021) as there is little evidence of the use and efficacy of such products on below-ground pests and pathogens (Toepfer et al, 2021). Further, more needs to be known in African smallholder systems on how soil type, soil quality and farmer management of soil health and fertility contribute to SPD, although studies from other areas show some promising findings (Watson et al, 2002;Janvier et al, 2007;Birkhofer et al, 2008;Huber et al, 2011).…”