Relationships between the emergence and oviposition of ectoparasitoid Spathius agrili Yang and its host emerald ash borer, Agrilus planipennis Fairmaire

Abstract

Relationships between the emergence and oviposition of ectoparasitoid Spathius agrili Yang and its host emerald ash borer, Agrilus planipennis Fairmaire Abstract Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), (= A. marcopoli Obenberger), is an important bark beetle attacking ash trees (Fraxinus spp.). It is very difficult to detect and control because of its highly concealed life history. This pest mainly distributed in partial Asian countries (China, Japan, Korea, Mongolia) and Far East Russia, while in China it presented in Heilongjiang, Jilin, Liaoning, Shandong, Inner Mongolia, Hebei, Taiwan Provinces and Tianjin City, etc. The important timber species F. mandshurica and gardening tree F. velutina were damaged severely in northern China. Spathius agrili Yang (Hymenoptera: Braconidae) is an important ectoparasitic wasp of the EAB larvae. This parasitoid has the potential to use as an excellent biological control agent for suppressing populations of EAB. The differences of emergence date between overwintered S. agrili and its host, parasitism rates at different periods, relations between parasitism rates and host densities, and relationships between ovipositions of braconid wasp and body sizes of host larvae were studied using methods of regular surveys in forests and observations in laboratory. Results revealed that the emergence of S. agrili was more than one month later than that of its host. It suggests good synchrony between parasitoid emergence and host availability. The overwintered S. agrili emerged from mid (in laboratory). The emergence date of parasitoid asynchronously inosculated with the optimum developmental instars of the earliest host larvae, which was the result of a long-term co-evolution between the two species. It was also suggested that the parasitoid S. agrili could be a specialized natural enemy for EAB. The natural parasitism rates on the whole gradually increased in field with time. The body sizes of host larvae, i.e. larval instar, affected the decision of parasitoid S. agrili to lay eggs or not. Under natural conditions, this parasitoid usually oviposited only on those host larvae with a prontum and body width more than 1.5 mm, and a body length in excess of 12 mm, i.e. the third or fourth instar larvae. These findings would consequentially contribute to the further successfully biological control of the trunk borer.

Occurrence of Emerald Ash Borer (Coleoptera: Buprestidae) and Biotic Factors Affecting Its Immature Stages in the Russian Far East

“…Previous Þeld studies conducted in northeast China showed that the two larval parasitoids (T. planipennisi and S. agrili) and one egg parasitoid (O. agrili) were the major biotic factors that caused high percentage parasitism (12Ð73%) of immature emerald ash borer larvae or eggs on infested green or velvet ash trees , Wang et al 2007). However, T. planipennisi and O. agrili were primarily found in the northern part of China (Liaoning and Jilin Provinces), while S. agrili was found Ϸ800 km further south in the Tianjian and Beijing areas (in Hebei Province).…”

“…Furthermore, these studies found that the three above mentioned Hymenoptera parasitoids inßicted a maximum of 73% mortality to emerald ash borer eggs and/or larvae infesting North American ash trees grown in Chinese plantation or landscapes , Wang et al 2007). These three Chinese parasitoid species have been introduced to the United States for classical biocontrol of emerald ash borer (USDA APHIS 2007, Bauer et al 2008.…”

“…These three Chinese parasitoid species have been introduced to the United States for classical biocontrol of emerald ash borer (USDA APHIS 2007, Bauer et al 2008. Although these parasitoids have established stable population at several U.S. locations, parasitism rates of emerald ash borer by the introduced Chinese parasitoids are considerably lower in newly introduced regions (1.5Ð5% in Duan et al 2010Duan et al , 2011 than rates (12Ð73%) reported from China , Wang et al 2007. While it remains to be seen if the classical biocontrol approach will eventually control emerald ash borer in the United States, more studies of emerald ash borer population dynamics and associated biotic factors in its native range may provide new biological control agents for management of this invasive pest in both native and invaded regions.…”

Sensilla on the antennae, legs and ovipositor of Spathius agrili Yang (Hymenoptera: Braconidae), a parasitoid of the emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)

“…EAB infested trees show no clear symptoms when the infestation is light, and this pest is therefore very difficult to detect and control (Wang et al, in press). Spathius agrili prefers EAB to other Agrilus species and has strong host searching and host finding abilities (Wang and Yang, 2005;Wang et al, 2006). The female wasps not only discover host larvae hidden inside bark and parasitize them successfully, but they also discriminate among host sizes and determine clutch size and progeny sex ratio accordingly (Wang et al, 2008a).…”

Hymenopteran Parasitoids Attacking the Invasive Emerald Ash Borer (Coleoptera: Buprestidae) in Western and Central Pennsylvania

“…Previous field studies conducted in the native range of EAB showed that several species of hymenopteran parasitoids were attacking immature stages (eggs and larvae) of EAB in Northeast China Wang et al 2007) and the Russian Far East (Duan 2012a). After safety-testing and regulatory approvals, 3 of these exotic parasitoid species, Spathius agrili Yang (Braconidae), Tetrastichus planipennisi Yang (Eulophidae), and Oobius agrili Zhang & Huang (Encyrtidae), were introduced from China to the U.S. for classical biocontrol of EAB (USDA APHIS 2007; Bauer et al 2008;Duan et al 2010Duan et al , 2012b.…”