Abstract
Higher volumes of conventional and novel chemical insecticides are applied by farmers to control resistant strains of armyworm (Spodoperta litura) in Pakistan without knowing their risks to the environment and to public health. Ten reduced-risk insecticides were tested for their compatibility with two entomopathogenic nematodes (EPNs); Heterorhabditis indica and Steinernema carpocapsae against S. litura. The insecticide emamectin benzoate was highly toxic (LC50 = 2.97 mg/l) against 3rd instar S. litura larvae when applied alone whereas, novaluron and methoxyfenozide were the least toxic (LC50 = 29.56 mg/l and 21.06 mg/l), respectively. All the insecticides proved harmless against the two EPNs even 96 h after treatment. Indoxacarb, flubendiamide and spinetoram produced the greatest mortalities (72–76%) of S. litura larvae after 72 h when applied in mixtures with H. indica. Lowest mortalities (44.00 ± 3.74% and 48.00 ± 2.89) were observed for mixtures of H. indica with methoxyfenozide and chlorfenapyr, respectively. The positive control treatments with both EPNs (S. carpocapsae and H. indica) produced > 50% mortality 96 h after treatment. For insecticide mixtures with S. carpocapsae, only indoxacarb produced 90% mortality of larvae, whereas, indoxacarb, flubendiamide, emamectin benzoate, and spinetoram produced 90–92% mortality of larvae when applied in mixtures with H. indica. Additive interactions (Chi-square < 3.84) of EPN mixtures with reduced volumes of reduced-risk insecticides suggest opportunities to develop more environmentally favorable pest management programs for S. litura.
Highlights
Spodoptera spp. (Lepidoptera: Noctuidae), commonly known as armyworms, are polyphagous insect pests, causing serious losses to many cash crops like cotton, maize, tobacco, groundnut, vegetables, legumes and fodder crops in Pakistan[1,2,3]
Considering the pest status of S. litura in Pakistan, and the challenge to overcome the resistance development and pesticide pollution, we investigated the compatibility of some selected insecticides with two entomopathogenic nematodes (EPNs) viz., S. carpocapsae and H. indica as part of an effective pest management strategy
The highest median lethal concentration (LC50 = 29.56 mg/l) was determined for the insecticide novaluron which was followed by methoxyfenozide (LC50 = 21.06 mg/l), whereas the toxicity scores of chlorfenapyr (LC50 = 17.16 mg/l), spinosad (LC50 = 14.78 mg/l) and indoxacarb ( LC50 = 10.92 mg/l) did not differ significantly from each other because of overlapping confidence intervals
Summary
Spodoptera spp. (Lepidoptera: Noctuidae), commonly known as armyworms, are polyphagous insect pests, causing serious losses to many cash crops like cotton, maize, tobacco, groundnut, vegetables, legumes and fodder crops in Pakistan[1,2,3]. EPNs belonging to genera Steinernema and Heterorhabditis are the most studied for their potential to control certain pests like armyworms (Spodoptera spp.)[7,11,12,14,15,16], diamondback moth (Plutella xylostella)[17,18], tomato leafminer (Tuta absoluta)[19,20,21], wax moth (Galleria mellonella), pink bollworm (Pectinophora gossypiella), eggplant fruit borer (Leucinodes arbonalis)[13], oriental beetle (Anomala orientalis), Japanese beetle (Popillia japonica), native masked chafer (Cyclocephala borealis)[22,23,24] and white grubs (Holotrichia parallela Motschulsky)[24] The compatibility of these EPNs with many insecticides has been widely studied against S. litura. Toxicity of the selected insecticides to S. litura larvae were determined alone and in mixtures with S. carpocapsae and H. indica under laboratory conditions
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