Influence of entomopathogenic fungus, Metarhizium anisopliae, alone and in combination with diatomaceous earth and thiamethoxam on mortality, progeny production, mycosis, and sporulation of the stored grain insect pests

Abstract

The stored grain insects cause great damage to grains under storage conditions. Synthetic insecticides and fumigants are considered as key measures to control these stored grain insect pests. However, the major issue with these chemicals is grain contamination with chemical residues and development of resistance by insect pests to these chemicals. Biological control is considered as a potential alternative to chemical control especially with the use of pathogens, alone or in combination with selective insecticides. The present study was conducted to evaluate the synergism of Metarhizium anisopliae with diatomaceous earth (DE) and thiamethoxam against four insect pests on the stored wheat grains. In the first bioassay, the M. anisopliae was applied at 1.4 × 10 and 1.4 × 10conidia/ml alone and in integration with two concentrations (250 and 500 ppm) of tested DE. The tested fungus when combined with DE and thiamethoxam possessed synergistic impact as compared to their individual efficacy. Adult mortality increased with respect to increased exposure interval and doses. In the second bioassay, M. anisopliae was applied at 1.4 × 10 conidia/ml individually and in combination with three concentrations (0.50, 0.75, and 1.00 ppm) of thiamethoxam. Results concluded that M. anisopliae integrated with DE and thiamethoxam provides more effective control of stored grain insect pests.

The Time–Concentration–Mortality Responses of Western Flower Thrips, Frankliniella occidentalis, to the Synergistic Interaction of Entomopathogenic Fungus Metarhizium flavoviride, Insecticides, and Diatomaceous Earth

“…These results were consistent with the studies reported by Athanassiou et al, in which a six-fold increase in adult mortality of T. confusum was observed when treated with B. bassiana and DE, compared with either B. bassiana or DE alone [15]. Similarly, Ashraf et al clearly indicated that M. anisopliae combined with DE or thiamethoxam had a synergistic effect, compared to their individual efficacies, and was more effective in controlling four stored insect pests [35]. Likewise, Wakil et al found that B. bassiana combined with DE or the neonicotinoid insecticide thiamethoxam increased the mortality of R. dominica adults, compared with individual treatments, and a significant additive effect was observed [32].…”

“…However, there have been few reports on its use in the control of agricultural pests. Our results showed that DE has a certain control effect on the invasive insect WFT, which is similar to its control effect against invasive red fire ants, whose efficacy was lower than stored grain insect pests [32,35,37,38]. The differences in control effects were due to the fact that some insects are more sensitive to DE, due to their anatomical and physiological characteristics, and may also be related to differences in the cuticular composition of different insect species [34,37].…”

“…As a natural insecticide, DE has been applied to control many stored grain insect pests, achieving a good control effect [32][33][34][35][36]. However, there have been few reports on its use in the control of agricultural pests.…”

“…DE has a good ability to absorb esters, and so it is a potential natural insecticide [30][31][32]. There are numerous reports, both domestic and foreign, which have indicated that DE has broad prospects for controlling a wide range of store-product pests, such as Tribolium confusum (J du Val), Tribolium castaneum (Herbst), Acanthoscelides obtectus (Say), Cryptolestes ferrugineus (Stephens), Sitophilus granarius (L.), and Rhyzopertha dominica (F.) [15,[33][34][35][36], as well as a variety of agricultural pests, such as Solenopsis invicta (Buren), Gryllidae (Bolívar), and Leptinotarsa decemlineata (Say) [37,38]. The insecticidal principle of DE is mainly to adsorb the cuticular lipids from the targeted insects; the tiny DE particles are trapped by the exposed cuticle surface of an insect, which causes various kinds of physical or mechanical damage and loosens the cuticle, causing loss of water and resulting in death [39][40][41][42][43].…”

“…Therefore, combining fungal biocontrol agents with adjuvants and Insects 2020, 11,93 3 of 20 other insecticides with good compatibility is an effective and reliable solution to improve the pest control effect [15,18,32,39,48]. Numerous studies have reported that the combination of EPF with insecticides [44,[48][49][50], DE [34,39,51,52], and with insecticides and DE have significantly improved their pest control efficacies [15,32,33,35]. For example, Nian et al [49] demonstrated that combining I. fumosorosea with sub-lethal doses of the insecticides beta-cypermethrin and bacillus thuringiensis caused synergistic effects against Plutella xylostella larvae under laboratory conditions.…”