Life-history traits in a parasitoid dipteran species with free-living and obligate parasitic immature stages

Abstract

The robber fly Mallophora ruficauda Weidemann (Diptera: Asilidae) is an important pest of apiculture in the Pampas of Argentina. As adults, they prey on honey bees and other insects, whereas the larvae are ectoparasitoids of Scarabaeidae grubs. Females of M. ruficauda lay eggs in grassland where the larvae drop to the ground after being wind‐dispersed and burrow underground searching for their hosts. A temporal asynchrony exists between the appearance of the parasitoid larvae and the host, with the parasitoid appearing earlier than the host. The present study investigates whether a strategy of synchronization with the host exists in M. ruficauda and determines which of the larval instars are responsible for it. Survival patterns and duration of the immature stages of the parasitoid are investigated to determine whether there is a modulation in the development at any time that could reduce the asynchrony. Experiments are carried out to determine the survival and duration of free‐living larval stadia in the absence of cues associated with the host. It is established that the first instar is capable of moulting to the second instar without feeding and in the absence of any cues related to the host, a unique event for parasitoids. Also, the first instar of M. ruficauda moults to the second stage within a narrow temporal window, and the second instar never moults in the absence of the host. After parasitizing a host, the second instar has the longest lifespan and is the most variable with respect to survival compared with the rest of the instars. All larval instars, except for those in the last (fifth) stadium, have a similar rate of mortality to that of second‐instar larvae. Additionally, it is established that the host is killed during the fourth (parasitoid) stadium and that the first‐ and fifth‐larval instars develop independently of the host. Finally, possible mechanisms that could aid in compensating for the asynchrony between the parasitoid and the host, promoting the host–parasitoid encounter, are discussed.

Behavioural plasticity induced by intraspecific competition in host orientation in a parasitoid

“…Only larvae between 20 and 25 days old were used because the survival rate is higher than 50% in larvae that are less than 32 days old, hence we guaranteed a good physiological state (Crespo & Castelo, 2010). Only larvae between 20 and 25 days old were used because the survival rate is higher than 50% in larvae that are less than 32 days old, hence we guaranteed a good physiological state (Crespo & Castelo, 2010).…”

“…Flasks containing larvae were kept in darkness under controlled temperature (25 ± 2 ∘ C, 65% ± 1% RH) until larvae reached the appropriate age. Only larvae between 20 and 25 days old were used because the survival rate is higher than 50% in larvae that are less than 32 days old, hence we guaranteed a good physiological state (Crespo & Castelo, 2010). Each larva was used only once in the experiments and then reared to be released in the field.…”

Functional sensorial complementation during host orientation in an Asilidae parasitoid larva

“…When springtime comes, soil temperature increases and the parasitoid accelerates its development rate, moults until reaching the fifth instar in a very short period of time (ca. 3 weeks) and kills the host (Crespo & Castelo, 2010). After, the parasitoid larva pupates and the adult emerges some time later.…”

Incidence of Non-Immunological Defenses of Soil White Grubs on Parasitism Success of Mallophora ruficauda Larva (Diptera: Asilidae)

“…After seven days of sun incubation, the egg hatches, and the tiny parasitoid larvae (1.35 mm length, 0.32 mm wide) drop to the soil dispersed by the wind [ 33 ]. Once on the soil, they rapidly bury themselves and search for the host’s microhabitat detecting chemicals from its posterior intestine [ 34 , 35 , 36 , 37 ]. Previous studies show that the first two larval instars are capable of surviving 39 days in average without association to the host [ 38 ].…”

“…It has also been established that there is a high parasitism preference for Cyclocephala signaticollis (Coleoptera: Scarabaeidae) because most of the parasitism occurs on this species independently of its availability in the field [ 32 , 35 ]. Furthermore, in laboratory experiments it has been shown that parasitoid larvae orientate mainly to volatile chemicals from the fermentation chamber of third instar C. signaticollis [ 36 , 37 ]. Also, orientation to odors from second instar C. signaticollis has been observed, but this response is not so intense [ 39 ].…”