The effect of strepsipteran parasitism on a tettigoniid pest of oil palm in Papua New Guinea

Abstract. A study was undertaken to assess the impact of the strepsipteran endoparasite Stichotrema dallatorreanum Hofeneder on the performance of its host Segestidea novaeguineae (Brancsik), a tettigoniid pest of oil palm in Papua New Guinea. This involved analyses of morphology, gut contents, body composition and reproductive variables of field-collected adults of stylopized and unstylopized hosts. The morphological consequences of stylopization by S. dallatorreanum included reduced wing, ovipositor and digestive tract lengths, whereas antennal length was largely unaffected. Feeding activity by the host, as estimated indirectly through weighing gut contents, was significantly reduced in parasitised female hosts, whereas smaller males showed no effect. Parasitized hosts had a reduced carcass dry weight associated with reduced nitrogen content and a substantial decline in carcass lipid content. Host reproductive variables were profoundly affected by stylopization. In females this included impaired ovarian development, reduced egg number and gonadal weight, the last of which was also reduced in males. There was an association between the number of S. dallatorreanum present (maximally six in males and nine in females) within a host and the extent of the impact of stylopization on most of the host characters investigated. The ability of S. dallatorreanum to reduce feeding and reproduction in the host suggests it may have potential use as a bio-control agent in the management of tettigoniid pests in Papua New Guinea.