INTERACTION OF CALYX FLUID AND VENOM FROM MICROPLITIS-CROCEIPES (BRACONIDAE) ON DEVELOPMENTAL DISRUPTION OF THE NATURAL HOST, HELIOCOVERPA ZEA, AND 2 ATYPICAL HOSTS, GALLERIA-MELLONELLA AND SPODOPTERA-EXIGUA

Polydnaviruses of many braconid and ichneumonid endoparasitoids play a n important role in the successful parasitism of their hosts. The host 's development is altered and its immune response is also suppressed. In this study, we compared the effects of calyx fluid and venom on the development of the natural host, Helicoverpa zea, and two atypical ho sts that the parasitoid does not normally attack in nature, Galleria m ellonella and Spodoptera exigua. The levels of calyx fluid and\or veno m injected was 0.05, 0.1 and 0.2 female equivalents (FE)/larva. In H. zea, calyx fluid significantly reduced larval growth on day 5 post inj ection. Venom alone did not affect larval growth but it synergized the action of calyx fluid by reducing growth earlier and for a longer per iod after injection. Other effects of calyx fluid on the host, either alone or in combination with venom, were an increase in developmental period, and a reduction in percent emergence and weight of adult moths . The percentage of H. tea larvae that pupated was not affected by cal yx fluid or venom. In Galleria mellonella, venom alone reduced larval growth comparable to calyx fluid and both tissues induced the effects on day 1 post injection. Other effects caused by calyx fluid or Venom alone or the combination were a reduction in percent pupation and emer gence, and the average adult weight. In S. exigua, high mortality occu rred when 4th instar larvae were injected. Although the injection of l arger fifth instars reduced overall mortality, the sham-injected larva e only gained weight during the first 24 hours after injection (from d ay 0 to day 1). However, adults were produced at all doses of calyx fl uid or venom. The effects of the virus on development in this species were a prolongation of the larval stage and reduction of adult weight by calyx fluid in combination with venom. In conclusion, injections of calyx fluid and venom of Microplitis croceipes can differentially aff ect the growth and development of its natural host H. zea, and atypica l host, G. mellonella, but only a minimal effect was observed in S. ex igua. Published by Elsevier Science Ltd.