Recent advances in the synthesis of insect pheromones: an overview from 2013 to 2022

Covering: 2013 to June 2022Pheromones are usually produced by insects in sub-microgram amounts, which prevents the elucidation of their structures by nuclear magnetic resonance (NMR). Instead, a synthetic reference material is needed to confirm the structure of the natural compounds. In addition, the provision of synthetic pheromones enables large-scale field trials for the development of environmentally friendly pest management tools. Because of these potential applications in pest control, insect pheromones are attractive targets for the development of synthetic procedures and the synthesis of these intraspecific chemical messengers has been at the core of numerous research efforts in the field of pheromone chemistry. The present review is a quick reference guide for the syntheses of insect pheromones published from 2013 to mid-2022, listing the synthesized compounds and highlighting current methodologies in organic synthesis, such as carbon-carbon coupling reactions, organo-transition metal chemistry including ring-closing olefin metathesis, asymmetric epoxidations and dihydroxylations, and enzymatic reactions.

Effect of Diets and Low Temperature Storage on Adult Performance and Immature Development of Phyllonorycter ringoniella in Laboratory

The Asiatic apple leaf miner, Phyllonorycter ringoniella (Matsumura), is an important insect pest to apples. We developed a rearing method for P. ringoniella in the laboratory. Overwintering pupae were collected from our apple orchard, and crabapple seedlings were selected as oviposition substrate and food source for the larval development. The mean developmental period was 25.9 ± 0.49 days from egg to adult and the survival rate was 0.387 under 25 ± 1 °C, 65 ± 5% RH and a photoperiod of 14:10 (L:D) h. Mean egg length and egg width were 0.336 ± 0.0043 and 0.259 ± 0.0046 mm, respectively. Mean body length and head width increased from 1.070 ± 0.0245 and 0.180 ± 0.0021 mm in first instar larvae to 5.027 ± 0.0718 and 0.321 ± 0.0021 mm in fifth instar larvae, respectively. The mean weight of the pupae was 0.946 ± 0.0132 mg. The wingspan of male adult (6.280 ± 0.0639 mm) was significantly larger than female (6.040 ± 0.0753 mm). The mean fecundity (56.9 ± 8.58 eggs per female) and longevity (8.2 ± 0.55 days) of females was highest when they were provided with 10% honey solution, followed by 10% sugar, water, and control. The females preferred to lay eggs (56.5 ± 3.84%) near the secondary leaf vein in a leaf. The larval mortality increased linearly (R² = 0.94) with the number of larvae per leaf. The mortality of pupae increased from 5.6 ± 4.01 to 51.1 ± 9.88% as storage periods at 4 °C increased from 0 to 105 days. The rearing method and its biological characteristics presented in this study will contribute to further studies on this pest insect.

Temperature-Dependent Development of Immature Phyllonorycter ringoniella (Lepidoptera: Gracillariidae) and Its Stage Transition Models

Asiatic apple leafminer, Phyllonorycter ringoniella (Matsumura), is an important insect pest of apple in Northeast Asia. Its larvae mine the leaves and are best managed by targeted sprays. Little is known about its thermal development characteristics, thus, immature P. ringoniella development was investigated under eight constant temperatures (13.3, 15.3, 20.7, 23.6, 26.1, 30.0, 32.3, and 35.0°C) in the laboratory. The total developmental period of the immature stage (egg-pupa) was inversely related to temperature and decreased from 76.4 d at 13.3°C to 25.9 d at 26.1°C. The developmental periods of eggs, larvae, and pupae ranged from 4.8 to 15.2, 15.5 to 40.3, and 5.7 to 21.6 d, respectively. Eggs, larvae, and pupae did not survive at 35.0°C. According to the ordinary linear model, the lower developmental threshold temperatures for egg, larva, pupa, and total immature stage were estimated as 6.7, 6.7, 9.6, and 7.1°C, and the thermal constants as 93.5, 286.5, 94.6, and 480.1 degree-days (DD), respectively. There were large differences among 11 nonlinear models for estimating lower and upper temperature thresholds, and small differences in estimating optimal temperature. Nonlinear temperature-dependent developmental rates were best represented by Lactin-1 model for egg and Briere-1 model for other stages. Stage transition models from eggs to adults of P. ringoniella were constructed by two-parameter Weibull function with the respective selected nonlinear developmental rate models. This study provides a fundamental understanding of thermal traits of P. ringoniella development which will be a useful tool to predict stage transition and for developing decision-based spray timings for integrated pest management.