Y a-t-il \'elimination d'Eupelmus orientalis Crawford par Eupelmus vuilleti Crawford (Hymenoptera : Eupelmidae) des syst\`emes de stockage du ni\'eb\'e (Vigna unguiculata Walp) ?

TL;DR

This study investigates the interactions among hymenopteran parasitoids in cowpea seed storage, revealing that Eupelmus vuilleti exhibits ovicide and larvicide behaviors affecting other species, but not E. orientalis, influencing biological control potential.

Contribution

It provides new insights into the behavioral interactions and population dynamics of Eupelmus species in stored cowpea seeds, highlighting implications for biological pest control.

Findings

E. orientalis is initially the most abundant species in storage.

E. vuilleti's population increases as E. orientalis disappears.

E. vuilleti exhibits ovicide and larvicide behaviors against D. basalis, but not E. orientalis.

Abstract

Ni\'eb\'e is a food leguminous plant cultivated in tropical Africa for its seeds rich in proteins. The main problem setted by its production is the conservation of harvests. In the fields as in the stocks, the seeds are destroyed by pests (bruchids). These bruchids are always associated with several entomophagous species of hymenoptera. Four entomophagous species were listed : an egg parasitoid (U lariophaga Stephan), and three solitary larval and pupal ectoparasitoids (D. Basalis Rondoni, Pteromalidae; E. vuilleti Crawford and E. orientalis Crawford, Eupelmidae). The survey of the populations shows that at the beginning of storage, E orientalis is the most abundant specie (72 %) whereas E. vuilleti and D. Basalis respectively represent 12 % and 16 % of the hymenoptera. During storage, the E orientalis population decreases gradually and it disappears completely in less than two months after the beginning of storage. E. Vuilleti population becomes gradually more important than D. basalis population which regress until less than 10 % of the emerging parasitoids. E vuilleti adopts ovicide and larvicide behaviour against D. Basalis. This behaviour explains its population regression inside granaries. If the aggressive behaviour of this Eupelmidae is a constant, that could also explain the disappearance of E orientalis. However if this species is maintained in stocks, it would be an effective control agent of bruchids according to their parasitic capacities. This study shows that ovicide and larvicide behaviour of E vuilleti is not expressed against E orientalis. When the females have exclusively the hosts already parasitized by E orientalis, they do not lay eggs. The disappearance of E orientalis could not thus be explained by the presence of E. vuilleti.