Zhen-De Yang

A Review of Invasive Biology, Prevalence and Management of Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae: Tetrastichinae)

The blue gum chalcid, Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae: Tetrastichinae) is widely distributed in Africa, America, Europe and Asia. Destructive damage of this wasp has been given much attention by many biologists and entomologists. We reviewed the invasive biology, distribution, mode of spread and situation of management of L. invasa in view of the status of rapid spread and serious damage. Research directions and methods of further studies were proposed, including reproductive mode and population expansion, impact factors and the formation mechanism of inducing gall, flight capacity of the wasp, effects of the ecological environment on distribution and occurrence, and control strategies. This information is beneficial to explore the mechanism of invasion and outbreak of invasive species.

Rapid identification of both sexes of Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae: Tetrastichinae) : a morphological perspective

The blue gum chalcid, Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae: Tetrastichinae) is a global pest in Eucalyptus plantations. Diverse modes of reproduction (thelytokous and sexual reproduction) are one of the advantages for rapid colonization and outbreak of this species. Understanding the reproductive strategies is advantageous for us to explore the invasive mechanisms. Importantly, how to identify both sexes of the species in the field is a crucial issue before we explore their reproductive strategies. In the current study, indexes of rapid identification of both sexes in L. invasa were studied. Results showed that the obvious differences in both sexes were the antenna and body size. Male wasps have three anelli and four funicular segments, but in females there are four and three segments, respectively. The longer male antennae, which are covered with longer and finer hairs than in the female, was also observed. Body, expansus, head, and gaster sizes of female wasps were significantly larger than the males. These results are an important base not only for exploring the reproductive strategies, but also for controlling L. invasa.

Parasitoids of the eucalyptus gall wasp Leptocybe invasa (Hymenoptera: Eulophidae) in China

Leptocybe invasa Fisher & La Salle (Hymenoptera, Eulophidae) is an invasive pest in Eucalyptus plantations throughout the world. Potential biological control agents for L. invasa were investigated in the Fujian, Guangdong, Hainan, Guangxi, Jiangxi, and Sichuan provinces of China, where Eucalyptus spp. have been severely damaged by the eucalyptus gall wasp. Three hymenopteran parasitoids of L. invasa were identified: Quadrastichus mendeli Kim & La Salle (Eulophidae), Aprostocetus causalis La Salle & Wu (Eulophidae), and Megastigmus viggianii Narendran & Sureshan (Torymidae); M. viggianii is newly recorded in China. The percentages of parasitization by Q. mendeli, A. causalis, and M. viggianii were 2.96%–19.53%, 2.30%–26.38%, and 24.93%, respectively. The longevity and body length of females were significantly greater than for males in A. causalis and M. viggianii. No males of Q. mendeli were found in China. These parasitoids could be used as biological agents for L. invasa in China.

Modeling climate change impacts on overwintering of Spodoptera exigua Hübner in regions of China

Inferential models are usually used to evaluate the effect of winter warming on range expansion of insects. Generally, correlative approaches used to predict changes in the distributions of organisms are based on the assumption that climatic boundaries are fixed. Spodoptera exigua Htibner (Lepidoptera: Noctuidae) overwinters as larvae or pupae in China regions. To understand the climate change impacts on overwintering of this species in regions of China, CLIMEX and Arc-GIS models were used to predict possible changes of distribution based on temperature. The climate change projection clearly indicated that the northern boundary of overwintering for S. exigua will shift northward from current distribution. Thus, the ongoing winter warming is likely to increase the frequency of S. exigua outbreaks.

Parasitoids of the eucalyptus gall wasp Leptocybe spp.: a global review

The genus Leptocybe Fisher & La Salle (Hymenoptera: Eulophidae) and its type species L. invasa were first described in 2004. Leptocybe spp. are global pests of eucalyptus plantations, and parasitoids play an important role in their control. In this review, we describe the species, distribution, biology, ecology and parasitism levels of Leptocybe spp. parasitoids and the problems associated with biological control programmes against Leptocybe spp. Additionally, prospects for the use of conservation or augmentative biological control programmes against Leptocybe spp. are discussed. Worldwide, approximately 23 species of parasitoids of Leptocybe spp. in 7 families and 10 genera have been found to date. Comparing the parasitism levels of the parasitoids showed that Quadrastichus mendeli, Selitrichodes neseri and several (approximately 4) native Megastigmus spp. could be exploited to manage Leptocybe spp. Available information on the Leptocybe spp. parasitoids is expected to improve our understanding related to ongoing studies of biological control programmes against Leptocybe spp.

Gal yapan bir psylloid Pseudophacopteron alstonium Yang et Li (Hemiptera: Phacopteronidae)’un, Alstonia scholaris (L.) R. Br. (Gentianales: Apocynaceae)’in kimyasal savunma yapısı üzerine etkisi

Plants and gall-induced insects have evolved some strategies to avoid each other’s defense systems. However, effects of a gall-induced insect on defensive resources in their host plants remain unclear. In this study, total phenolic and tannin, peroxidase, superoxide dismutase, catalase and polyphenol oxidase of gall (G) and non-galled (NG) tissues in one leaf, whole leaf with gall (WG) from 1 st to 5 th stages induced by Pseudophacopteron alstonium , and un-galled leaves (UL) were measured in laboratory. Results showed that high levels of secondary metabolites (i.e., total phenolic and tannin) and protective enzymes in galls were detected. Contents of secondary metabolites and protective enzymes of galls increased sharply from the 1 st to 3 rd stages of galls and subsequently decreased when nymph stops feeding or enters into a mature stage at the 4 th or 5 th stages. These high levels of secondary metabolites and protective enzymes maybe were the defensive response when A. scholaris attacked by P. alstonium . All of these findings are helpful for understanding the interaction between plants and gall-formed insects.

Effect of a gall-inducing psylloid, Pseudophacopteron alstonium Yang et Li (Hemiptera: Phacopteronidae) on defensive chemistry of Alstonia scholaris (L.) R. Br. (Gentianales: Apocynaceae)

Plants and gall-induced insects have evolved some strategies to avoid each other’s defense systems. However, effects of a gall-induced insect on defensive resources in their host plants remain unclear. In this study, total phenolic and tannin, peroxidase, superoxide dismutase, catalase and polyphenol oxidase of gall (G) and non-galled (NG) tissues in one leaf, whole leaf with gall (WG) from 1 st to 5 th stages induced by Pseudophacopteron alstonium , and un-galled leaves (UL) were measured in laboratory. Results showed that high levels of secondary metabolites (i.e., total phenolic and tannin) and protective enzymes in galls were detected. Contents of secondary metabolites and protective enzymes of galls increased sharply from the 1 st to 3 rd stages of galls and subsequently decreased when nymph stops feeding or enters into a mature stage at the 4 th or 5 th stages. These high levels of secondary metabolites and protective enzymes maybe were the defensive response when A. scholaris attacked by P. alstonium . All of these findings are helpful for understanding the interaction between plants and gall-formed insects.