Biology and developmental strategies of the palaearctic parasitoid Bracon nigricans (Hymenoptera: Braconidae) on the neotropical moth Tuta absoluta (Lepidoptera: Gelechiidae)

During the years following the invasion of Western Palaearctic tomato crops by the South American tomato leafminer (TLM), Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), several indigenous, generalist parasitoids have been recorded on this new host. Among these, Bracon nigricans Szépligeti (Hymenoptera: Braconidae) is widely distributed in the Palaearctic region, and has been frequently recovered from TLM. However, most of the available data on this species deal with taxonomic aspects and its recovery in faunistic surveys. The present study documents the biology of B. nigricans on TLM, and provides a scientific basis for its inclusion in TLM management programs in Afro-Eurasia. We studied several B. nigricans life history traits relevant to juvenile development and reproduction by females. Bracon nigricans proved to be an idiobiont, synovigenic, ectoparasitoid of mature TLM larvae. Several B. nigricans reproductive traits were influenced by the age of the mothers; on average the progeny had a slightly male-biased sex-ratio (60% males) and a low rate of successful development (~37%). Adult females lived 42.8 d and produced an average of 29.8 offspring. These biological parameters yielded an Intrinsic rate of increase of 0.052. Females showed behavioral plasticity in host use, as initial host paralysis was followed by host-feeding, oviposition, or host rejection, with a consequent high mortality rate among hosts exposed to parasitism. Although further field studies are needed, these data, obtained in laboratory conditions, suggest that B. nigricans should be considered as a potential biological control agent of TLM in newly invaded areas of the Palaearctic region.