Development of the anal vesicle, salivary glands and gut in the egg-larval parasitoid Chelonus inanitus: tools to take up nutrients and to manipulate the host?

Reproductive Biology and Rearing Improvements of Apanteles opuntiarum, Potential Biocontrol Agent of the Argentine Cactus Moth, Cactoblastis cactorum

The cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) is native to South America and has been used as a biocontrol agent of Opuntia (Cactaceae) in Australia and South Africa. Its invasion in North America has raised concerns for the native Opuntia in the USA and Mexico. We investigated the reproductive biology and rearing procedures of a host-specific potential biocontrol agent, Apanteles opuntiarum Martínez and Berta (Hymenoptera: Braconidae). Given the gregarious nature of the parasitoid larvae, we studied the morphology of the immature stages and evaluated evidence of polyembryony and superparasitism. We also investigated the effects of host exposure arena and host density on parasitism rates and wasp production. The morphological descriptions provide a basis for comparison with other species. Early larval instars of A. opuntiarum are similar to other microgastrine immature stages. However, the mature larva exhibits placoid sensilla in the epistomal region, a unique character not previously reported. We provide evidence that A. opuntiarum eggs are not polyembryonic; females frequently superparasitize and have an oviposition preference for larvae parasitized 1-2 d previously. Exposing larvae of C. cactorum to wasps while inside the cactus resulted in lower parasitism and fewer offspring from each host than exposing larvae in the arena without the cactus. Parasitism and mortality rates were higher at lower host densities, possibly due to reduced host group defensive behavior. These results suggest that preference for superparasitism, host defensive behavior, and interactions with the cactus may play an important role in per-host wasp production under laboratory conditions.

Regulation of the Larval Transcriptome of Diatraea saccharalis (Lepidoptera: Crambidae) by Maternal and Other Factors of the Parasitoid Cotesia flavipes (Hymenoptera: Braconidae)

Koinobiont endoparasitoid wasps regulate the host's physiology to their own benefit during their growth and development, using maternal, immature and/or derived-tissue weaponry. The tools used to subdue the wasps' hosts interfere directly with host transcription activity. The broad range of host tissues and pathways affected impedes our overall understanding of the host-regulation process during parasitoid development. Next-generation sequencing and de novo transcriptomes are helpful approaches to broad questions, including in non-model organisms. In the present study, we used Illumina sequencing to assemble a de novo reference transcriptome of the sugarcane borer Diatraea saccharalis, to investigate the regulation of host gene expression by the larval endoparasitoid Cotesia flavipes. We obtained 174,809,358 reads and assembled 144,116 transcripts, of which 44,325 were putatively identified as lepidopteran genes and represented a substantial number of pathways that are well described in other lepidopteran species. Comparative transcriptome analyses of unparasitized versus parasitized larvae identified 1,432 transcripts of D. saccharalis that were up-regulated under parasitization by C. flavipes, while 1,027 transcripts were down-regulated. Comparison of the transcriptomes of unparasitized and pseudoparasitized D. saccharalis larvae led to the identification of 1,253 up-regulated transcripts and 972 down-regulated transcripts in the pseudoparasitized larvae. Analysis of the differentially expressed transcripts showed that C. flavipes regulated several pathways, including the Ca+2 transduction signaling pathway, glycolysis/gluconeogenesis, chitin metabolism, and hormone biosynthesis and degradation, as well as the immune system, allowing us to identify key target genes involved in the metabolism and development of D. saccharalis.

Demonstration of cytotoxicity against wasps by pierisin-1: a possible defense factor in the cabbage white butterfly

The cabbage white butterfly, Pieris rapae, produces pierisin-1, a protein inducing apoptosis of mammalian cells. In the present study, the biological activity of pierisin-1 as a protective agent against parasitic wasps for P. rapae was examined. Pierisin-1 caused detrimental effects on eggs and larvae of non-habitual parasitoids for P. rapae, Glyptapanteles pallipes, Cotesia kariyai and Cotesia plutellae at 1-100 µg/ml, levels essentially equivalent to those found in P. rapae larvae. In contrast, eggs and larvae of the natural parasitoid of P. rapae, Cotesia glomerata proved resistant to the toxicity of pierisin-1 through inhibition of pierisin-1 penetration of the surface layer. The expression level of pierisin-1 mRNA in the larvae of P. rapae was increased by parasitization by C. plutellae, whereas it was decreased by C. glomerata. In addition, C. plutellae was associated with elevation of activated pierisin-1 in the hemolymph. From these observations, it is suggested that pierisin-1 could contribute as a defense factor against parasitization by some type of wasps in P. rapae.

Biological study of Plutella xylostella (L.) (Lep: Plutellidae) and it's solitary endoparasitoid, Cotesia vestalis (Haliday) (Hym. Braconidae) under laboratory conditions

Plutella xylostella (L.) (Lep: Plutellidae), is a destructive pest of brassicaceous crops in the world. Cotesia vestalis (Haliday) is one of most important biological control agents of P. xylostella in the world and Iran. Both of P. xylostella and C. vestalis biology were carried out in laboratory condition. Results showed that development time of immature stages of P. xylostella including egg, Instar I, Instar II, Instar III, Instar IV, prepupa, pupa were 2.39 +/- 0.17, 2.18 +/- 0.17, 2.06 +/- 0.28, 2.14 +/- 0.14, 2.54 +/- 0.12, 0.40 +/- 0.12 and 4.23 +/- 0.23 days, respectively. Longevity of female and male were 28.26 +/- 0.05 and 30.22 +/- 0.05 days. By dissecting the parasitized larvae, the egg incubation period of C. vestalis was recorded 1.73 +/- 0.06 days. In long-term oviposition trials, females laid eggs on P. xylostella larvae for up to 10 days. Larval development of the parasitoid in host only required 6.47 days: the first instar larva required 3.25 +/- 0.047 days; the second instar larva needed 2.78 +/- 0.1 days and the third instar larvae exited the host and pupated in, 0.4 +/- 0.07 days. Prepupal and pupal period of wasp were 1.9 +/- 0.06 and 2.13 +/- 0.09 day, respectively. Unmated female and male longevity of wasp were 16.83 +/- 0.37, 16.25 +/- 0.17 and sex ratio is male-biased. When a mixed group and isolated of instars were presented for parasitoid, the 2nd and 3rd instar larvae were so preferred and the 4th instar was less attractive for selection. In choice experiment, the percentage parasitism of 2nd, 3rd and 4th instars was 78.58, 69.94 and 4.36%, respectively. The rapid oviposition rate, short life duration and high percentage parasitism increases parasitoid potential for suppression of host population. Present results suggest that C. vestalis has considerable potential as a biological control agent for P. xylostella.

Stage dependent influences of polydnaviruses and the parasitoid larva on host ecdysteroids

In the solitary egg-larval parasitoid Chelonus inanitus (Braconidae) both polydnavirus and the parasitoid larva manipulate host development. Parasitization leads to a premature drop in juvenile hormone titre and a precocious onset of metamorphosis in the 5th larval instar. The C. inanitus bracovirus (CiBV) alone causes a reduction in host ecdysteroid titres at the pupal cell formation stage and prevents pupation. Here we report three new findings. (1) We show that parasitization causes a reduction in haemolymph ecdysteroid titre immediately after the moult to the 5th instar; similarly low values were seen in nonparasitized larvae after the moult to the 6th instar. These data along with parasitoid removal experiments indicate that the low ecdysteroid titre after the moult is a very early sign of the upcoming metamorphosis. (2) In vitro experiments with prothoracic glands and brain extracts showed that CiBV affects both prothoracic glands and prothoracicotropic hormone after the stage of pupal cell formation. (3) In the haemolymph of parasitized larvae the ecdysteroid titre increased in the late cell formation stage, i.e. immediately before egression of the parasitoid. In vitro experiments showed that late 2nd instar parasitoids release ecdysteroids and are thus very likely responsible for the rise in host ecdysteroids.