Host utilization, reproductive biology, and development of the larval parasitoid Tetrastichus planipennisi as influenced by temperature: implications for biological control of the emerald ash borer in North America.
The success of classical biological control programs depends in part on understanding climate effects on introduced agents. Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), a larval endoparasitoid of emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is being introduced to EAB-invaded regions of the United States (USA) and Canada for biological control. To optimize regional release strategies and increase efficiency of the EAB-biocontrol program, we determined the effects of five constant temperatures from 15°C to 35°C on T. planipennisi parasitism rate, development, adult longevity, and fecundity in EAB. Results showed a decrease in parasitoid development time from 139.8 days at 15°C to 26.3 days at 30°C, while no parasitoid eggs hatched at 35°C. Parasitism rates, provisioned with an excess of host larvae throughout their life, increased from 1.4% at 15°C to 28% at 30°C then declined to 0.5% at 35°C. Adult parasitoid longevity declined from 24 weeks at 15°C to <2 weeks at 35°C. Fertility table analyses revealed T. planipennisi net reproductive rate was highest at 25°C, and intrinsic and finite rates of increase were highest at 30°C, suggesting 25-30°C as optimal rearing temperatures for this parasitoid. Combining these results with temperature data from climate zones of 3-7 in the USA, we predicted T. planipennisi can complete more than one generation in all locations in these climatic zones, with more generations in warmer climates. Moreover, our findings also suggest that despite the availability of suitable EAB larval stages for parasitism, releases of T. planipennisi in early spring or late fall in cold climate zones may be suboptimal due to low temperatures, as may mid-summer releases in hot climate zones due to high temperatures.