Apriona germari is an important boring insect and a major threat to more than 20 kinds of trees, including mulberry, poplar, and apple trees. It is widely distributed in China, where it causes serious damage. Difficulties in the detection and monitoring of boring insects are major obstacles to the prediction and control of infestations. Thus, it is important to develop trapping devices incorporating behavioral chemicals (e.g. sex pheromones, plant attractants) as bait. However, to date, no effective compounds suitable for monitoring the behavior of this insect have been reported. The purpose of this study was to analyze the principal volatile compounds of its host plants and to identify the most effective plant attractants for monitoring insect numbers, as a basis for forecast and control.
Apriona germari adults consume nutrients to reach sexual maturity and then, to achieve reproductive success, they must migrate to other trees to lay their eggs. The shoots of plants within the family Moraceae are rich in protein and represent an important source of nutrients for newly emerged Apriona germari. The volatiles of four important host plants in this family, Morus alba, Broussonetia papyrifera, Cudrania tricuspidata and Ficus carica, were analyzed using ATD-GC-MS. The relative levels of individual chemical components were determined using normalization methods. In total, 56 different compounds were identified in the four plants, of which 31 were present in Morus alba, 30 in Broussonetia papyrifera, 29 in Cudrania tricuspidata, and 27 in Ficus carica. They were divided into four major categories: alcohols, aldehydes, alkenes, and esters. The plants differed in their 'chemical fingerprints’, characterized by specific types and content of volatiles. The major volatile components of Morus alba were alcohols (25.06%) and esters (66.61%), accounting for 91.67% of the total; in Broussonetia papyrifera, alkenes (46.22%) and esters (39.59%) accounted for 87.81% of the total; in Cudrania tricuspidata, alcohols (11.80%), aldehydes (22.92%), alkenes (36.15%) and acids (14.58%) accounted for 85.45% of the total; and in Ficus carica, alkenes (33.25%), esters (33.36%) and phenols (18.06%), accounted for 84.77% of the total. Among all four plants, the most common constituents were vinyl compounds. Compared with the other three species, Ficus carica volatiles had lower total contents of ketones and alkanes and Cudrania tricuspidata had a lower content of esters. Importantly, 11 of the volatiles were common to all four plants. These were: leaf alcohol, capryl alcohol, benzaldehyde, 1-nonanal, decanal, 1-octene, ocimene, leaf acetate, hexadecane, 2,6-di-tert-butyl-4-methylphenol and 2,4-di-tert-butylphenol. The total quantities of these 11 compounds accounted for 79.98% of their total volatiles in M. alba, 60.43% in B. papyrifera, 34.62% in C. tricuspidata, and 45.97% in F. carica.
Volatile odors of host plants are important chemical signals that have great significance for the survival and development of insects. They play important roles in insect-host orientation, nutrition, breeding, and other aspects of environmental positioning. Many studies have shown that it is possible to obtain insect attractants by analyzing and extracting the volatiles of their host plants. It seems likely that a suitable signal compound could be obtained from these 11 compounds, either singly or in combinations mixed in specific proportions.