Influence of Temperature and Humidity on the Efficacy of Spinosad Against Four Stored-Grain Beetle Species

Abstract

In the present work, we examined the insecticidal effect of spinosad, against adults of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) on wheat and the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae) on maize. The dose rates used were 0.01, 0.1, 0.5 and 1 ppm. The bioassays were carried out at three temperatures, 20, 25 and 30°C and two relative humidity levels, 55 and 75%. Mortality of R. dominica and S. oryzae was high even at 0.01 ppm of spinosad, reaching 100% at 55% relative humidity and 30° after 21 days of exposure. Generally, mortality of R. dominica, increased with temperature while for S. oryzae mortality increased with temperature and with the decrease of relative humidity. Moreover, for S. oryzae, mortality was low at 20°C. In the case of T. confusum, mortality was low at doses between 0.01 and 0.5 ppm even after 21 days of exposure. At 1 ppm, mortality exceeded 90% only at 30°C and only after 21 days of exposure. Mortality of P. truncatus was low on maize treated with 0.01 ppm, but increasing the dose to 0.1 ppm resulted in > 87% mortality after 14 days of exposure. In several combinations tested, spinosad efficacy notably varied according to the temperature and humidity regimes. Of the species tested, R. dominica and P. truncatus were very susceptible to spinosad, followed by S. oryzae, while T. confusum was the least susceptible.

Isolation and identification of fungal growth on Tribolium castaneum in stored wheat flour

“…Long chain hydrocarbons help in or play an important role in initial attachment of the entomopathogenic fungal spores to cuticle given that such dry phialocondia attach in nonspecific manner through hydrophobic interaction (Lord, 2001 and2009;Shah and Pell, 2003). The chemical, biological or physical treatments for controlling the insects during storage may contribute towards reducing spread of fungal spores within the storage system (Huang et al, 1997;Athanassiou et al, 2008;Brijwani et al, 2010;Mohale et al, 2010;Beckett, 2011;Villers, 2014).…”

Effect of temperature on the toxicity of several insecticides to <i>Apolygus lucorum</i> (Heteroptera: Miridae)

“…For instance, although increasing temperatures appear to enhance e cacy of organophosphates, spinosad, or abamectin, this is not always true with pyrethroids. [24][25][26][27][28] ese temperature-dependent di erences may be due to changes in coverage, 29) insect behavior, 30) or insecticide toxicity. 31) Within the range of the temperatures studied, higher temperatures lead to increased insect activity.…”

Efficacy of spinosad and methoprene, applied alone or in combination, against six stored-product insect species

“…This rate of 1 ppm will kill adults and limit progeny production of several major stored-grain insect pests, including R. dominica, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae), and S. oryzae (Fang et al 2002a, b;Athanassiou et al 2008a, b, c;Kavallieratos et al 2010). However, 1 ppm spinosad will not completely control red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), confused flour beetle, Tribolium confusum Jacquelin du Val, O. surinamensis, C. ferrugineus, or psocids such as Liposcelis bostrychophila (Badonnel) (Psocoptera: Liposcelididae), but will generally eliminate progeny production by these species (Fang et al 2002a, b;Athanassiou et al, 2008bAthanassiou et al, , 2009Daglish 2008).…”