Biotic potential of Trissolcus japonicus Ashmead (Hymenoptera: Scelionidae), a solitary egg parasitoid of the brown marmorated stink bug, Halyomorpha halys (Stål)

The brown marmorated stink bug, Halyomorpha halys (Stål) is an invasive pest with a wide host range including many economically important crops.   Trissolcus japonicus, an egg parasitoid wasp, is a potential biological control agent but little is known of its biotic potential.   Naïve, 24-h-old female wasps were mated overnight with adult sex ratios of 1:1 (males: females).  Females were exposed to 24-h-old egg masses for 24 h.  Parasitism rates decreased with consecutive egg masses.  When there was at least a week between egg masses, parasitism rates were very high on the first egg mass after the break and then decreased as before.  The maximum biotic potential was 100 and the minimum was 53 eggs per female.  This differs from literature counts of 42.2 eggs per female.  Wasps emerged 18 to 28 d after oviposition with 20 the median for males and 24 for females.  Our study has shown that the biotic potential is at least double of what had been recorded, even though the biotic potential for a female’s entire lifespan was not reached.  Further research would include offering more egg masses to females over a longer period of time to try to find total biotic potential.  If T. japonicus is found to be specific to its host (native stink bugs are currently being tested), it could be an excellent biological control agent.  This parasitoid can have over 10 generations per yr, whereas the BMSB has a maximum of two generations per yr, and has a strongly female-biased sex ratio.