Biology of Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae): A facultative Hyperparasitoid of stem borers

Abstract

The biology of the parasitoid Tetrastichus howardi, which was introduced from the Philippines into South Africa for the biological control of the stem borer Chilo partellus, was studied in the laboratory. On average, a T. howardi female produced 101 progeny (92% females) which developed in 4.3 hosts. The upper threshold temperature for development was around 33°C, the minimum threshold was calculated as 12.8°C and the thermal constant as 239.8 day‐degrees. With hosts, females lived 23.6 and males 16.7 days. T. howardi was found to be a facultative hyperparasitoid with a very wide host range. As a primary parasitoid, it developed in pupae of various Lepidoptera as well as Coleoptera and Hymenoptera and as a hyperparasitoid in dipteran and hymenopteran parasitoids. A linear relation was found between the number of emergent parasitoids and the volume of the host from which they emerged. Preference tests indicated that T. howardi preferred to parasitize the phytophagous insects C. partellus and Heliothis armigera, over their parasitoids Xanthopimpla stemmator and Palexorista laxa. The host selection of inexperienced T. howardi females was different from the experienced parasitoids. When given a choice, females showed preference for the host species they were allowed to parasitize previously and the host species from which they had been reared. The use of facultative hyperparasitoids in biological control in general and against stem borers in South Africa in particular is discussed.

Keywords:

• biological control
• Chilo partellus
• facultative hyperparasitoid
• stem borer
• Tetrastichus howardi