Bacillus thuringiensis (Bt) has been used as sprayable pesticides for many decades. Bt strains utilized in these products produce multiple insecticidal proteins to complement a narrow insect specificity of each protein. In the late 1990s, genes encoding Bt insecticidal proteins were expressed in crop plants such as cotton and corn to protect these crops from insect damage. The first Bt protein used in transgenic cotton was Cry1Ac to control Heliothis virescens (tobacco budworm). Cry1Ab was applied to corn to control Ostrinia nubilalis (European corn borer). Since these insects have developed resistance to Cry1Ac and Cry1Ab, new Bt proteins are required to overcome the resistance. In order to protect corn furthermore, it is desired to control Diabrotica virgifera (Western corn rootworm), Helicoverpa zea (corn earworm) and Spodoptera frugiperda (fall armyworm). Recently, many new Bt insecticidal proteins have been discovered, but most of them require protein engineering to meet the high activity standard for commercialization. The engineering process for higher activity necessary for Bt crops is called optimization. The seed industry has been optimizing Bt insecticidal proteins to improve their insecticidal activity. In this review, several optimization projects, which have led to substantial activity increases of Bt insecticidal proteins, are described.

The effects of external factors such as temperature, humidity, pesticide formulation, and pesticide concentration on the contact angle of pesticide droplets on rice leaf surfaces were analyzed. The experiments showed that there were significant differences in the contact angles of droplets on the leaf surfaces under different temperatures and humidity. As the ambient temperature increased, the contact angle first decreased and then increased, reaching a minimum value at 25°C. With a gradual increase in humidity, the contact angle significantly increased and reached a maximum at 100% humidity. Finally, it was concluded that both the formulation and concentration of the pesticide had a significant effect on the contact angle of droplets on rice leaf surfaces. The experiments also illustrated that the effects of the pesticide formulation and concentration on the contact angle were more significant than those of temperature and humidity.

The purpose of this study was to demonstrate the inhibitory effect of chemicals on methane emissions in paddy soil. We found that (4-hydroxyphenyl) chloromethanesulfonate (C-1) has a methanogenic inhibition activity, and we studied its inhibition mechanism using laboratory tests. The study found that C-1 treatment of flooded soil did not significantly affect the bacterial community but rather the archaeal community; particularly, Methanosarcina spp. C-1 strongly inhibited the aceticlastic methanogenesis route. It was suggested that the inhibitory target of C-1 was different from the well-known methanogenic inhibitor 2-bromoethanesulfonate, which targets methyl-coenzyme M reductase of methanogen. In addition, C-1 had a secondary effect of inhibiting the dechlorination of chlorophenols. Although field trials are required as the next development step, C-1 can be used to reduce methane emissions from paddy fields, one of the largest sources in the agricultural sector.

γ-Aminobutyric acid receptors (GABARs) mediate fast inhibitory neurotransmission and are targets for insecticides. GABARs are composed of five subunits, the composition of which dictates the pharmacological characteristics of GABARs. Both competitive and noncompetitive GABAR antagonists can be used as insecticides. Gabazine is a potent competitive antagonist of mammalian α1β2γ2 GABARs; however, it is less potent against insect GABARs. To explore how gabazine interacts with GABARs, we examined whether the sensitivity of the small brown planthopper (Laodelphax striatellus) RDL GABAR (LsRDLR) to gabazine is increased when its amino acid residues are substituted with α1β2γ2 GABAR residues. In the results, two of the generated mutants showed enhanced gabazine sensitivity. Docking simulations of gabazine using LsRDLR homology models and an α1β2γ2 GABAR cryo-EM structure revealed that the accommodation of gabazine into the “aromatic box” in the orthosteric site lowered the binding energy. This information may help in designing GABAR-targeting insecticides with novel modes of action.

The ability to predict the environmental behavior of chemicals precisely is important for realizing more rational regulation. In this study, the bioaccumulation of nine chemicals of different molecular weights absorbed via the intestinal tract was evaluated in fish using the everted gut sac method. The amounts of chemicals that passed through the intestinal membrane after a 24-hr exposure were significantly decreased for chemicals with MW≥548 and D_{max min}≥15.8 Å (or D_{max aver}≥17.2 Å). These thresholds are consistent with those previously proposed in terms of MW (>800) and molecular size (D_{max min}>15.6 Å or D_{max aver}>17.1 Å) for the limit of permeable chemicals through the gill membrane. The results show that the same MW and D_max criteria can be used to predict low bioaccumulation through both the gill membrane and the intestinal tract. These findings are helpful in reducing the need to conduct animal tests in environmental safety studies.

Orius insidiosus, known as the pirate bug, is widely distributed throughout the Americas. It is employed for the biological control of Frankliniella occidentalis in organic berry crops in Mexico. In conventional crops, spinosad is the main control method for this pest. The LD₅₀ of spinosad on O. insidiosus was determined. In addition, we monitored the population density of F. occidentalis in blackberry crops under two types of management (biochemical+mass trapping, and biological control). The LD₅₀ was 225.65 ppm 3.8 times greater than the 60 ppm dose commonly used in blackberry crops. Both types of control are efficient; however, spinosad is less effective and should be combined with other environmentally friendly strategies. The possibility of combining chromatic traps+spinosad application and chromatic traps+strategic release of O. insidiosus to effectively control thrips without compromising fruit quality is discussed.