Biology of the galling wasp Tetramesa romana, a biological control agent of giant reed

The biology of the gall-forming wasp Tetramesa romana Walker (Hymenoptera: Eurytomidae) from southern France and Spain was studied to determine its suitability as a biological control agent of giant reed (Arundo donax L.), an exotic and invasive riparian weed in the US and Mexico. Females produced eggs parthenogenetically and deposited them into shoot tips. Eggs were 1.26 mm long and hatched within 5 days of oviposition. The larvae completed three instars within 23–27 days, with the first and second instars lasting 5 days each at 27 °C and the third instar lasting 12 days. Larvae increased in length from 0.9 mm to 4.1 mm between the first and last instars. The total generation time averaged 33 days. Adults were 6.8 mm long with antennae and lived 3.7 days. Spanish wasps lived 1.3 days longer than French wasps. Most (80%) parthenogenetic reproduction involved wasps that were less than 5 days old. A total of 36% of French wasps tested and 65% of Spanish wasps produced offspring. Individual Spanish wasps produced an average of 26 (up to 66) progeny, displaying an intrinsic capacity for increase of 0.081 and a population doubling time of 9.2 days. Over 90% of exit holes made by emerging wasps were located within two nodes of the shoot tip. Reproductive wasps made 2.5-fold more probes than did wasps that failed to gall stems, and probing behavior was 13% more prevalent in the afternoon than in the morning. The Spanish genotypes of T. romana are particularly suitable for mass production to support field releases.