Spit, J., A. Philips, N. Wynant, D. Santos, G. Plaetinck, J. Vanden Broeck.  Insect Biochemistry and Molecular Biology 81: 103-116, http://dx.doi.org/10.1016/j.ibmb.2017.01.004

The responsiveness towards orally delivered dsRNA and the potency of a subsequent environmental RNA interference (RNAi) response strongly differs between different insect species. While some species are very sensitive to dsRNA delivery through the diet, others are not. The underlying reasons for this may vary, but degradation of dsRNA by nucleases in the gut lumen is believed to play a crucial role. The Colorado potato beetle, Leptinotarsa decemlineata, is a voracious defoliator of potato crops worldwide, and is currently under investigation for novel control methods based on dsRNA treatments. Here we describe the identification and characterization of two nuclease genes exclusively expressed in the gut of this pest species. Removal of nuclease activity in adults increased the sensitivity towards dsRNA and resulted in improved protection of potato plants. A similar strategy in the desert locust, Schistocerca gregaria, for which we show a far more potent nuclease activity in the gut juice, did however not lead to an improvement of the RNAi response. Possible reasons for this are discussed. Taken together, the present data confirm a negative effect of nucleases in the gut on the environmental RNAi response, and further suggest that interfering with this activity is a strategy worth pursuing for improving RNAi efficacy in insect pest control applications.

 

Arain, M.S., Wan, PJ., Shakeel, M. et al. Phytoparasitica (2017). doi:10.1007/s12600-016-0560-z

The speed of toxic action of an insecticide is an indicator for control efficacy and has considerable practical importance. For agricultural pest control, fast-acting is an important feature for an insecticide to consistently reduce the amount of feeding damage. Butene-fipronil is a novel compound obtained via the structural modification of fipronil. However, information about the toxicity and speed of toxic action is still limited. In the present paper, we compared the toxic feature of butene-fipronil with seven other insecticides, of which imidacloprid and abamectin are slow-acting insecticides, and acephate, endosulfan, methomyl, α-cypermethrin and spinosad are fast-acting insecticides. We found that the contact and stomach toxicities of butene-fipronil were among the highest ever estimated to Leptinotarsa decemlineata and Drosophila melanogaster. The speed of toxic action of butene-fipronil was determined using median lethal time (LT50) at a dose (concentration) equivalent to LD80 values. For L. decemlineata, the values for butene-fipronil, imidacloprid, abamectin, acephate, endosulfan, methomyl, cypermethrin and spinosad were calculated to be 39.9, 36.5, 37.5, 20.2, 22.4, 23.8, 16.4 and 23.1 h, respectively. Those for D. melanogaster were 29.8, 31.5, 29.4, 14.0, 20.3, 18.1, 13.5, and 20.1 h, respectively. ANOVA analysis showed that butene-fipronil, imidacloprid, abamectin had similar LT50 values, whereas acephate, endosulfan, methomyl, spinosad and cypermethrin had comparable LT50 values. Thus, butene-fipronil belongs to slow-acting insecticides. Our results provide more empirical information for butene-fipronil potential application.

Skuhrovec, J., Douda, O., Pavela, R. et al. Am. J. Potato Res. (2016). doi:10.1007/s12230-016-9549-x

The effect of essential oil (EO) from anise (Pimpinellia anisum) on the mortality of young larvae of Colorado potato beetles has been studied. In our bioassays, P. anisum EO significantly increased the mortality of the second instar larvae of L. decemlineata. Significantly different values of LD50 and LD90 were established for acute (LD50 = 1.76, and LD90 = 8.29) as well as chronic toxicity (LD50 = 0.45, and LD90 = 1.01). Decrease of both values over experimental period was evident, which showed that the larval mortality was slow and cumulative. The composition of EO used for biological experiments was also assessed. The main component detected in EO from P. anisum was anethole (79.87%), followed by anisaldehyde (7.74%), estragole (5.88%) and β-linalool (1.07%). Within five days, residual concentration of EO decreased from 3.87 mg/g of dry weight immediately after foliar applications to 0.9 mg per g of dry weight. The effect of this slow evaporation could be explained by dominant presence of anethole or by the type of formulation and the addition of oil and tween. Results of our study demonstrate that EO from P. anisum has insecticidal properties that may lead to the development of new organic products for the control of Colorado potato beetles.