Rearing Larvae of the Avian Nest Parasite,Philornis downsi(Diptera: Muscidae), on Chicken Blood-Based Diets

Abstract

Captive rearing of insect pests is necessary to understand their biology and to develop control methods. The avian nest fly, Philornis downsi Dodge and Aitken, is a blood-sucking parasite during its larval stage and a serious threat to endemic birds in the Galapagos Islands where it is considered invasive. In order to procure large numbers of flies for biological studies, rearing media and diets were trialed for rearing the larval stage of P. downsi under controlled conditions in the absence of its avian host. P. downsi eggs were obtained from field-caught female flies, and once eggs hatched they were reared on chicken blood for the first 3 d. Following this, three diets were tested on second- and third-instar larvae: 1) chicken blood only; 2) chicken blood, hydrolyzed protein and dried milk powder; and 3) chicken blood, hydrolyzed protein and brewer’s yeast. Out of 385 P. downsi larvae tested, we were able to rear 50 larvae to the adult stage. The highest level of mortality was found in the first-instar larvae. Survivorship of second- and third-instar larvae was similar irrespective of diet and diet did not significantly influence larval or pupal development times; though larvae fed the diet with brewer’s yeast developed marginally faster. Pupal weights were similar to those of larvae that had developed on bird hosts in the field. To our knowledge, this is the first effective protocol for rearing a hematophagous parasitic avian fly from egg to adult in the absence of a living host.

Evidence for rapid downward fecundity selection in an ectoparasite (Philornis downsi) with earlier host mortality in Darwin’s finches

“…Adult P. downsi flies are vegetarian and feed on decaying plant material, so they do not pose a direct threat to Darwin's finches (Couri, ; Skidmore, ). However, the fly oviposits in active finch nests when the attending female is absent (Lahuatte et al, ; O’Connor, Robertson, & Kleindorfer, ; O'Connor, Robertson, & Kleindorfer, ), and multiple female flies may oviposit in a single nest (Dudaniec, Gardner, & Kleindorfer, ). After P. downsi eggs hatch, 1st‐instar larvae enter the nares and body cavities of the nestling and reside there to feed on blood and tissue (Fessl, Sinclair, & Kleindorfer, ).…”

“…trunk or abdomen) that are functionally linked to fecundity (Olsson, Shine, Wapstra, Ujvari, & Madsen, 2002;Parker et al, 2011;Preziosi, Fairbairn, Roff, & Brennan, 1996;Winkler, Stölting, & Wilson, 2012). Parasitic insects provide useful systems to test ideas about effects of body size on fecundity because parasite diets can be tracked through host availability (Nijhout, 2003;Lahuatte, Lincango, Heimpel, & Causton, 2016). In this way, parasitic insects can provide insights into changing body size and fecundity with altered nutritional conditions.…”

Host‐specific associations affect the microbiome of Philornis downsi, an introduced parasite to the Galápagos Islands

“…The age class of each larva was assessed in the field and verified back in the laboratory based on the presence and colour of the posterior spiracles (e.g., Kleindorfer et al., ). Adult females ( n = 5) were trapped in February 2014 using papaya‐baited McPhail traps (see Lahuatte et al., for methods) positioned at several locations around El Barranco on the island of Santa Cruz (0°44′34.1″S, 90°18′10.4″W, elevation: 15–41 m.a.s.l.) and preserved in 95% ethanol until processed.…”

“…The fly was accidentally introduced to the Galápagos Islands circa 1960s (Causton et al., ; Kleindorfer & Sulloway, ), but was first observed in Darwin's finch nests in 1997 (Fessl, Couri, & Tebbich, ). Adult P. downsi flies feed on decaying fruit as opposed to their parasitic, nest‐dwelling larvae, which require frequent bloodmeals from developing nestlings before pupating in the nest (Fessl, Sinclair, & Kleindorfer, ; Lahuatte, Lincango, Heimpel, & Causton, ). Since 2000, the number of P. downsi larvae per endemic finch nest has increased by 46% in nests, and direct mortality over this period is documented at 55% of nestlings due to larval parasitism (reviewed in Kleindorfer & Dudaniec, ).…”

“…To date, control options include treating nests with permethrin insecticide (Causton & Lincango, ; Knutie, McNew, Bartlow, Vargas, & Clayton, ; O'Connor, Robertson, & Kleindorfer, ), biological control using natural enemies (Bulgarella et al., ), and trapping adult flies (Causton et al., ; Kleindorfer, Peters, Hohl, & Sulloway, ), while there is ongoing research to develop more effective trapping techniques (Cha et al., ). At the same time, a fly breeding program is underway to understand the fly's reproductive biology in greater detail (Causton et al., ; Lahuatte et al., ) to evaluate the possibility of using the sterile insect technique. A novel approach that may be an instrumental and targeted method to control P. downsi could be via manipulation of the fly's microbiome in order to decrease the parasite's resistance to host defences or environmental stressors, as similarly proposed for insect vectors of transmissible diseases (e.g., Clayton et al., ; Wang et al., ).…”