Host refractoriness of the tobacco hornworm, Manduca sexta, to the braconid endoparasitoid Cotesia flavipes

Abstract

Cotesia flavipes (Hymenoptera:Braconidae) is a gregarious endoparasitoid of several pyralid stemborer larvae of economic significance including the sugarcane borer, Diatraea saccharalis. In this study, the ability of this parasitoid to develop in a sphingid host, Manduca sexta, was tested. First, second, third, fourth, and even pharate fifth instar host tobacco hornworm larvae were readily parasitized by the female C. flavipes parasitoids but no wasp larvae hatched from the eggs in this refractory host. Instead, the parasitoid eggs were invariably encapsulated by the host's hemocytes and, ultimately, no parasitoids emerged from tobacco hornworm hosts. The first stages of encapsulation were evident at 2 h post-parasitization of the host M. sexta larvae, when the beginning stages of capsule formation were seen. The developmental fate of the host larvae with encapsulated parasitoids was variable. Most succumbed as abnormally small fifth instars or as post-wandering prepupal animals, while a few developed normally to the pupal stage. Dissection of all the larvae or pupae with encapsulated wasp eggs showed evidence of hemocytic encapsulation and melanization of the C. flavipes eggs. This report describes the association between C. flavipes and M. sexta, which appears to be an excellent model system for studying the physiological processes accompanying wasp egg encapsulation that result in death of the host as well as the parasitoid. Since the parasitoid egg never hatches, the system offers an excellent opportunity to identify and study the effects of parasitoid-injected polydnavirus and venom on host physiology.

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

“…Cotesia flavipes also affects the host cellular and humoral immune response by affecting the total hemocyte population and phenoloxidase activity (Mahmoud et al, 2011, 2012). The suppression of the immune system of D. saccharalis by C. flavipes is highly effective, but the efficiency in escaping host immune response (egg encapsulation) is reduced in Diatraea grandiosella (Dyar) (Lepidoptera: Crambidae) (Alleyne and Wiedenmann, 2001) and completely ineffective in avoiding encapsulation by larvae of Ostrinia nubilalis (Walker) (Lepidoptera: Pyralidae) (Alleyne and Wiedenmann, 2001) and Manduca sexta (L.) (Lepidoptera: Sphingidae) (Rodríguez-Pérez et al, 2005). Like other species in the flavipes complex, C. flavipes is also associated with a polydnavirus (Cônsoli and Kitajima, 2006).…”

Research Article ITS2 as a molecular marker for the identification of Diatraea saccharalis and D. flavipennella and possible infection with Cotesia spp.

“…Rodríguez-Pérez et al (2005), in a study with C. flavipes and Manduca sexta, observed that parasitism was unable to induce host immunosuppression in the non-habitual host. In habitual hosts, as D. saccharalis, parasitism induces host immunosuppression that is required to prevent encapsulation of Cotesia parasitoid (Alleyne and Wiedenmann, 2001b;White and Wilson, 2012).…”

The biochemical basis of antimicrobial responses in Manduca sexta

“…Since high levels of antimicrobial peptides are unavailable in the initial phase of host defense to destroy the invaders, hemocyte-mediated immune responses (i.e. phagocytosis, nodulation and encapsulation) are critical for the survival of host insects (Lavine & Strand, 2002;Amaya et al, 2005;RodrÍguez-Pérez, 2005). In the tobacco hornworm, a small population of plasmatocytes is responsible for sequestering the majority of injected E. coli or Staphylococcus aureus (Dean et al, 2004): one such cell can engulf as many as 500 killed bacteria.…”