Combined use of the larvo‐pupal parasitoids Diachasmimorpha longicaudata and Aganaspis daci for biological control of the medfly

Abstract

In biological control programmes, it is very common to employ multiple species to manage a single insect pest. However, the beneficial effects of natural enemies are not always additive because of several factors, including interspecific competition between these biocontrol agents.For this reason, in the present study we assessed several biological parameters (percentage parasitism, fertility, induced mortality and population reduction) of the parasitoids Diachasmimorpha longicaudata and Aganaspis daci when used together against the medfly Ceratitis capitata under laboratory and greenhouse conditions. Our results showed that, under laboratory conditions, fertility and percentage parasitism corresponded to a different functional response for each species (D. longicaudata: type II; A. daci: type III), whilst under greenhouse conditions, and unlike what occurs with single releases, both parasitoids showed a type III functional response; this is the only response which may lead to direct density dependence when host densities are low.Our results also revealed that when both species acted together, they produced a very high total percentage parasitism compared to that reported for single releases under both laboratory (64-76%) and greenhouse (21-51%) conditions. The parasitism was also higher for A. daci except when medfly larvae were provided in an artificial diet. Furthermore, host mortality induced by the two parasitoids acting together was very high, especially at low-host densities; medfly population was almost completely reduced under greenhouse conditions. In summary, the data reported here supports the combined use of these species in biological control programmes against the medfly and highlights the importance of several factors, such as climatic conditions and host density, when planning their field releases.

A Minor Role of Host Fruit on the Parasitic Performance of Aganaspis daci (Hymenoptera: Figitidae) on Medfly Larvae

“…Results showed, again, no significant differences among fruits in A. daci parasitic performance, even though we should highlight the numerally higher effective fertility and parasitoidism in apple and orange and the substantial induced mortality observed in peach. However, the values obtained in these trials for all fruits were surprisingly low compared with previous studies with the same experimental design [ 59 , 60 ]. This poor performance cannot be attributed to the host fruit species or to intrinsic factors of parasitoids, as previous studies have used apples and individuals of the same age and with the same parasitic experience as those used in this work.…”

“…This was contrary to expectations considering the longer ovipositor of this braconid [ 9 , 69 , 70 ], the hypothesis of Sivinski [ 71 ] that parasitoids with short ovipositor can only infest the larvae found in small fruits and the high firmness of the mesocarp in apples [ 65 ]. As in de Pedro et al [ 60 ], we should conclude that the advanced sensillar equipment of A. daci [ 55 ] makes this parasitoid very efficient at searching for hosts inside fruit, most probably allowing a better detection of larvae even in fruits of significant size.…”

“…Under controlled conditions, the reduction of medfly populations caused by A. daci females was above 70% in every tested fruit, suggesting that physical properties of all these fruits are suitable for an adequate activity of this parasitoid. However, in greenhouse trials simulating natural conditions, the parasitic performance was very poor, which, considering similar previous studies [ 59 , 60 ], may be attributed to some environmental factor that could have negatively affected A. daci survival, development or parasitic ability. Thus, despite a certain host fruit preference being determined for each type of trial (with a slight dominance of apples in all cases), the effect of host fruit species on the parasitic performance of A. daci seems to be less relevant than, for example, that of environmental factors.…”

“…Our results, in which mean population reduction was above 70% in all cases, suggest that the physical properties of all the fruits tested are suitable for high parasitic activity of A. daci on the medfly. This had already been proved for peaches [ 22 ] and apples [ 59 , 60 ], on which A. daci had already shown higher parasitoidism rates than D. longicaudata when released together [ 60 ]. This was contrary to expectations considering the longer ovipositor of this braconid [ 9 , 69 , 70 ], the hypothesis of Sivinski [ 71 ] that parasitoids with short ovipositor can only infest the larvae found in small fruits and the high firmness of the mesocarp in apples [ 65 ].…”

“…This species had been previously observed parasitizing larvae from the genus Bactrocera Macquart on mango and cempedak in its area of origin [ 9 ], on guava in Egypt [ 15 ], and even on olive fruits in laboratory trials in Greece [ 58 ]. Moreover, A. daci has been reported emerging from larvae of C. capitata on figs [ 18 , 20 ], citrus [ 20 ], apples [ 59 , 60 ], loquats, guavas, grapefruits, and peaches [ 21 , 22 ].…”