Morphological Variation Of Hyalopterus Pruni (Geoffroy) (Hemiptera:Aphididae)

The relationships between insects and plants are extremely complicated. As a large class of typical phytophagous insects in parasitic way, most aphid species have more than one kind of host plant. The host selection as an important part of aphid feeding behavior, has always been a hot topic of studying the relationship between aphids and their host plants. The selected host plant not only be a source of nutrients for aphids, as well as to provide a site for aphid populations’growth and reproduction. The host plant is the small habitat for aphids, while the external environments of host plant are also closely related with aphids growth and development of During the long-term evolutionary process, morphological characteristics may have been changed among different aphid populations with the differences in environmental conditions. So host plant and geographical distribution of aphid populations should not be ignored. It’s of great theoretical and realistic significance to explore the influence of feeding preference, host plants and geographical distribution to morphological variation on aphids.Hyalopterus pruni (Geoffroy) (Hemiptera:Aphididae), the peach mealy aphid, is a common agricultural pest that is widely dispersed in China and Europe. Three kinds of host plants were selected as the representative host plants in this study:Amygdalus persica L. var. scleropersica (Reich.) Yii et Lu (primary host), Prunus cerasifera Ehrhar f.atropurpurea (Jacq.) Rehd. (primary host), and Phragmites australis (Cav.) Trin. ex Steud. (secondary host). The leaf disc test was used to determine the feeding preferences of different H. pruni populations with peach, plum or reeds leaves. At the same time, morphological variation of specimens collected from 3 different host plants was selected and quantified by principal component analysis, hierarchical cluster analysis and canonical discriminate analysis of morphological characteristics such as body length (BODYL), body width (BODYW), length of antennal segments and length of leg segments. In addition, the mitochondrial COI gene sequences of 30 aphid populations were compared. The main research contents and results were as below:1. Feeding preference of Hyalopterus pruniWhen fed with 3 kinds of host foliage, there were some differences between the highest total numbers of H. pruni on 3 kinds of host plant leaf discs. When the experiment carried out at 80th minute, the highest number (20.67 averagely) of H. pruni collected on peach trees was reached. At 50th minute, the highest amount (14.67) of H. pruni collected on plum foliage was reached. The highest number was reached to 19.33 of H. pruni collected on reeds when passed 50 minutes. In addition, there were differences in selectivity of H. pruni collected from 3 host plants. Aphids had an obvious preference for reeds irrespective of the host plant they were collected on. H. pruni collected on reeds and peach trees preferred peach to plum foliage, but those collected on plum trees displayed no significant preference between peach and plum leaves.2. Morphological variation between Hyalopterus pruni collected from different host plantsMorphological analysis detected significant differences between 5 morphological characteristics of H. pruni populations collected on peach, plum and reeds in Shanghai (P<0.05):the length of antennal II (ANTLII), length of terminal antennal VI (PTL), basal length of ultimate rostral (URSL), length of fore tarsal I (FTIL) and length of middle tibia (MTL). Aforementioned characteristics were mainly related to foraging and attached on the surface of the host plants. The results of principal component analysis showed that the top seven principal components collectively comprising up to 80.269% of the total variance. It can able to reflect the major part of morphological variation information. Furthermore, cluster and canonical discriminate analysis showed that H. pruni collected on reeds can be objectively separated from those collected on peach and plum trees. Our inability to distinguish H. pruni feeding on peaches and plums maybe because these plant species belong to the same family.There were extremely significant differences between 11 morphological characteristics of H. pruni populations collected on 3 kinds of host plants in East China (P<0.01). H. pruni feeding on reeds had relatively longer antenna, legs and relatively wider basal ultimate rostra. And those feeding on peach foliage took second place, while those feeding on plum foliage had the shortest antenna, legs and the relatively narrow basal ultimate rostra. Moreover, basal ultimate rostra of H. pruni collected on peach trees were the longest, and those feeding on plum foliage took second place. H. pruni feeding on reeds had the shortest basal ultimate rostra. H. pruni feeding on plum trees differed significantly from those feeding on peaches and reeds in the body length(BODYL), length of middle tarsal II(MTIIL) and length of hind claw (HCL), but there was not any significant difference between H. pruni feeding on peach and reeds foliage detected in morphological analysis (P>0.05). The results of principal component analysis showed that the top six principal components collectively comprising up to 85.849% of the total variance. Besides, cluster analysis showed that there was a strong correlation between H. pruni collected on peach and reeds, while those feeding on plum trees can be objectively separated from those collected on peach and reeds foliage. Above results were in agreement with the consequences of ANOVA and multiple comparisons. Canonical discriminate analysis indicated that there was a strong correlation between H. pruni collected on peach and plum trees which both belong to the rosaceous plants, so the selected 13 morphological characteristics could be used as the basis of distinguishing H. pruni collected on different families host plants.3. Morphological variation between Hyalopterus pruni collected from different geographical regionsThere was no significant difference between 33 morphological characteristics of H. pruni populations collected in East China (P>0.05). An extremely significant difference was found in the length of middle tibia (MTL) (P<0.01).Morphological analysis did not detect any significant differences between H. pruni feeding on peach and plum foliage (P>0.05). However, the aphid population collected from Jiangxi province differed significantly from those collected from others in the length of middle tibia (MTL). Comparatively speaking, geographic distribution had less effect on the morphological variation of H. pruni populations. The results of multiple comparisons showed that host plants had greater impact than geographical distribution on morphological variation of H. pruni populations. Furthermore, cluster analysis indicated that H. pruni collected from Jiangxi province could be objectively separated from those collected from others.4. Genetic differentiation of mitochondrial COIThere were 21 variable sites based on mitochondrial COI gene sequence alignments of H. pruni populations collected on plum trees in Shandong and Anhui province. In this study,2 haplotypes were identified of all the samples. The genetic distance between aforementioned populations and the rest H. pruni populations was 0.03295. In addition, the phyletic evolution analysis showed that the relationship of populations collected on plum trees in the northern part of East China were more closer with each other while they were far with other 26 H. pruni populations.In summary, some differences were existed in foraging 3 types of host plants of different H. pruni populations. Morphological analysis detected significant differences between some characteristics of H. pruni populations collected on peach, plum and reeds. Compared with host plants, geographical distribution had less effect on the morphological variation of H. pruni populations. Besides, differences were detected between H. pruni collected on plum trees in the northern part of East China and other H. pruni populations.