Approaches for the biological control of stored product pests

Abstract

Stored products include all postharvest agricultural foodstuffs that do not require refrigeration and that can be preserved for several months under proper conditions as cereal grain and other raw material or processed food. Regrettably, in the Mediterranean region, the presence of insect pests such as the internal feeders of grain: Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), Sitophilus spp. (S. granarius (L.), S. oryzae (L.) and S. zeamais (Motschulsky)) (Coleoptera: Curculionidae) and Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae) as well as the moth usually present in warehouses and grain mills, Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae), induce important quantitative and qualitative damage before consumption. Among the integrated pest management strategies for the control of these concerning stored product pests, biological control with the introduction of parasitoids as natural enemies represents a good alternative to the use of pesticides. Unfortunately, for the correct implementation and success of this sustainable approach, higher management knowledge is required. For this reason, the aim of this thesis was to assess different biological control approaches for the control of the most important stored product pests. A major issue for the cereal industry is the early detection of insects during grain storage and processing, especially when immature stages of the pests are hidden inside the grain kernels, such as happens with the internal feeders. Then, the first two chapters of this thesis are dedicated to the development of two Polymerase Chain Reaction (PCR) methodologies for internal feeder’s diagnosis. First, in chapter 1, a realtime PCR (qPCR) protocol for the detection and quantification of R. dominica in rice as a model system to quantify internal feeders in grain with a simple methodology is presented. On the other side, in chapter 2, a multiplex PCR protocol for the simultaneous detection and identification of the five most prevalent internal feeder pest species in different grains and processed food is described and then, also tested with commercial samples. For the effective use of natural enemies it is vital to understand and consider the interactions among physical, chemical and biological factors that take place when the grain is stored. For this reason, the third chapter of the thesis is focused on assessing the effectiveness of the parasitoid Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae) released in three different densities (10♀♀, 20♀♀ or 40♀♀ parasitoids) to control high infestations of the weevils R. dominica and S. zeamais in two kilos of rice under two risk temperatures (23ºC and 28ºC). The last chapter of the thesis is devoted to the optimization of an economic and easy to use device called Bankerbox for the control of the moth E. kuehniella by rearing and progressively releasing the parasitoid Habrobracon hebetor (Hüber) (Hymenoptera: Braconidae). In this perfectionated Bankerbox version, to avoid the risk of contamination of the stored products, Galleria mellonella (Lepidoptera: Pyralidae) larvae was chosen as host to rear the parasitoid. Then, three different treatments were tested, one with E. kuehniella 4th instar larvae and two with G. mellonella: one containing 4th instar larvae and the other with mixed larval stages (2nd and 4th instar larvae). The research carried out in this thesis attends to increase the knowledge for the proper use of integrated pest management strategies by providing feasible alternatives to the use of pesticides in the stored product industry for the control stored product pests.