Xia-Lin Zheng

Effect of soil moisture on overwintering pupae in Spodoptera exigua (Lepidoptera: Noctuidae)

Spodoptera exigua Hübner (Lepidoptera: Noctuidae), can overwinter as pupae at depths of 0- to 5-cm beneath the ground. In order to understand the effect of soil moisture on the overwintering success of this species, we tested the supercooling point and survival of pupae, and the growth rate of prepupae that were exposed to different temperature and soil moisture in the laboratory. Results showed that supercooling points, body water contents, and survivals after the different pre-treatments were not significantly affected by the soil moisture. The developmental progress of prepupae, survival of prepupae and pupae were negatively correlated with soil moisture as well as the delay of exposure time, which supports the hypothesis that soil moisture acts as a developmental modulator. We presumed that the delay of pupation and lower prepupae survival under higher soil moisture was due to lack of a complete pupal chamber for protection at low temperatures. Low pupal survival was likely attributed to lack of oxygen in the soil, especially under the condition of higher soil moisture. We suggest that using strategies of irrigation and soil tillage during winter may decrease the overwintering population of S. exigua from the perspective of integrated pest management.

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.

Male-Biased Capture in Light Traps in Spodoptera exigua (Lepidoptera: Noctuidae): Results from the Studies of Reproductive Activities

Nocturnal insects show phototactic behavior. Interestingly, males are caught by light traps more often than females in many species. In the present study, the male-biased capture in light traps in the field was evaluated to test the hypothesis that male-biased capture was associated with the reproductive activities of Spodoptera exigua. During a 16-wk. period in 2011, a total of 5075 moths caught by light traps in the field revealed a significant male-biased capture. However, the sex ratio of the natural population was not significantly different from 1:1 from July to October 2011. The ratio of moths caught per hour by light traps showed that females were captured in the first half of the night, whereas the peak capture by light traps for males occurred in the second half of the night. Among the captured adults, the percentage of unmated females was significantly lower than that of the mated females and males. Experiments in the laboratory indicated that the time of activities for both sexes was consistent with the active patterns of oviposition and copulation. The percentage of flight-to-light of the unmated females was significantly lower than that of the mated females and males. Thus, the lower capture of the unmated females, which is associated with reduced positive phototactic responses of S. exigua, probably is one of the reasons resulting in the male-biased sex ratio in light traps.

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.

Effects of the larval host plant on the supercooling capacity and physiological characteristics of beet armyworm pupae, Spodoptera exigua (Lepidoptera: Noctuidae)

The beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), is a serious economic pest worldwide that overwinters as pupae in temperate regions. There is no information on the relationship between the larval host plant and the cold hardiness of S. exigua pupae (pre-overwintering feeding), whereas the acclimation temperature, thermoperiod, photoperiod, and soil moisture level are known to influence cold hardiness. Larvae incubated at 20, 23, and 26°C with a L12:D12 photoperiod were fed one of four host plants (pakchoi, cabbage, shallot and spinach) to determine the effect of larval host plant on energy reserves, supercooling capacity, and cryoprotectant level of pupae. The interaction between temperature and larval host plant was significant in regard to pupal fresh weight (FW), glycogen, lipid, supercooling point (SCP), body water content (BWC), and glycerol levels. Higher FW and glycerol content and lower SCP of pupae that were fed as larvae on pakchoi were observed at the lowest rearing temperature. Moreover, higher glycogen content of pupae from larvae reared on pakchoi was also observed at the highest rearing temperature. Glycerol and glycogen contents of pupae from larvae fed on pakchoi were negatively correlated with temperature. Our results suggest that S. exigua pupae enhance their low temperature tolerance by decreasing their SCP and accumulating cryoprotectant (i.e., glycerol) allowing the animals to tolerate the harsh environmental conditions of winter, provided that the overwintering generation of larvae fed on suitable host plants.

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.