Charles Adarkwah

Potential of Hymenopteran larval and egg parasitoids to control stored-product beetle and moth infestation in jute bags.

The control of stored-product moths in bagged commodities is difficult because the developmental stages of the moths are protected by the bagging material from control measures such as the application of contact insecticides. Studies were carried out to assess the ability of Hymenopteran parasitoids to locate their hosts inside jute bags in the laboratory. The ability of different parasitoids to penetrate jute bags containing rice was investigated in a controlled climate chamber. Few Habrobracon hebetor (Say) (Hymenoptera: Braconidae) passed through the jute material while a high percentage of Lariophagus distinguendus (Förster), Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae), Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae) and Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) were able to enter the Petri-dishes. Significantly more L. distinguendus and T. elegans entered compared to H. hebetor. There was significant difference in the mean percentage parasitoids invading depending on species. Head capsules and/or thorax widths were measured in order to determine whether the opening in the jute material would be large enough for entry of the parasitoids. These morphometric data differed depending on parasitoid species and sex. The parasitoid Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae) did not enter the bags, but located host larvae inside the jute bags and parasitized rice moths Corcyra cephalonica larvae by stinging through the jute material. Venturia canescens significantly reduced the number of C. cephalonica adults emerging from the bagged rice; therefore, it could be released in storage rooms containing bagged rice for biological control of C. cephalonica. The use of parasitoids to suppress stored-product insect pests in bagged commodities could become a valuable supplement to the use of synthetic pesticides.

Ability of the larval ectoparasitoid Habrobracon hebetor (Say, 1836) (Hymenoptera: Braconidae) to locate the rice moth Corcyra cephalonica (Stainton, 1865) (Lepidoptera: Pyralidae) in bagged and bulk stored rice

The potential of using Habrobracon hebetor for the inundative biological control of Corcyra cephalonica in rice stored in jute bags and in bulk was assessed. Host-finding in the situation of bag storage was tested by preparing small jute bags measuring 18 · 16 cm filled with 5 kg of un-infested rice grains. In the first experiment, 60 larvae of C. cephalonica were released into the bag. The bag was placed in an empty climatized room with an area of 12.3 m2. Sixty H. hebetor adults (sex ratio of 1 male: 2 females) were released at a distance of 1.6 m away from the jute bag. The number of H. hebetor adults that entered the jute bag was counted daily for 8 days by opening the bag and counting the parasitoids. Only 3% of the parasi- toids entered the jute bag. In a second experiment, 60 C. cephalonica larvae were placed inside a wire gauze cage within the jute bag. Ten H. hebetor adults were released into the jute bag. The bag was sealed. After 1 week the cage was removed, and the number of C. cephalonica as well as F1 generation of H. hebetor that emerged was recorded. H. hebetor was able to significantly reduce the number of C. cephalonica emerging from the bagged rice; the corrected mortality due to the parasitoid release was 92.13%. The emergence of H. hebetor progeny started on day 9 after the introduction of the parasitoids and continued until day 21.Host-finding in the situation of bulk rice was tested in glass cylinders (50 cm height, Ø = 25 cm) containing caged larvae at horizontal depths of 7 and 14 cm. H. hebetor was able to find its host C. cephalonica in both depths; significantly more F1 H. hebetor adults emerged from hosts placed 7 cm deep. The implications of these results with respect to the suitability of H. hebetor for the biological control of C. cephalonica in bagged and bulk rice are discussed.Zusammenfassungp]Das Potential der Mehlmottenschlupfwespe Habrobracon hebetor für die inundative biologische Bekämpfung der Reismotte Corcyra cephalonica in Reis gelagert in Jutesäcken oder geschuttet wurde untersucht. Die Wirtsfindung bei Sacklagerung wurde mit Hilfe kleiner Jutesacke mit den Maßen 18 · 16 cm getestet, die mit 5 kg unbefallenem Reis gefüllt wurden. In einem ersten Experiment wurden sechzig Reismottenlarven in den Sack entlassen. Der Sack wurde in einen leeren Klimaraum mit einer Grundfläche von 12,3 m2 gelagert. Sechzig Imagines von H. hebetor (Geschlechterverhältnis ein Männchen zu zwei Weibchen) wurden in 1.6 m Entfernung des Sacks freigelassen. Die Anzahl H. hebetor in den Säcken wurde über 8 Tage täglich gezählt, indem die Säcke geöffnet wurden. Nur 3% der Parasitoide drangen in den Jutesack ein. In einem zweiten Experiment wurden 60 Larven von C. cephalonica gekäfigt und im Innern des Jutesacks deponiert. Zehn Imagines von H. hebetor wurden in den Sack entlassen, welcher daraufhin verschlossen wurde. Nach 1 Woche wurde der Käfig entnommen und die Anzahl geschlüpfter C. cephalonica und F1 H. hebetor gezählt. H. hebetor reduzierte signifikant die Anzahl von C. cephalonica; die korrigierte Mortalität betrug 92.13%. Der Schlupf der Nachkommen von H. hebetor begann am 9. Tag nach Freilassung und hielt bis zum 21. Tag an. Die Wirtsfindung in geschüttetem Reis wurde in Glaszylindern (Höhe 50 cm, Ø = 25 cm) getestet, in denen in 7 and 14 cm Tiefe gekäfigte Reismottenlarven eingebracht wurden. H. hebetor konnte die Wirte in beiden Tiefen erreichen; signifikant mehr F1 H. hebetor schlüpften von Wirten in 7 cm Tiefe. Die Bedeutung der Ergebnisse für die Eignung von H. hebetor für die biologische Bekämpfung der Reismotte in geschüttetem und gesacktem Reis wird diskutiert.

Bioefficacy of enhanced diatomaceous earth and botanical powders on the mortality and progeny production of Acanthoscelides obtectus (Coleoptera: Chrysomelidae), Sitophilus granarius (Coleoptera: Dryophthoridae) and Tribolium castaneum (Coleoptera: Tenebrionidae) in stored grain cereals

Food losses caused by insects during postharvest storage are of paramount economic importance worldwide, especially in Africa. Laboratory bioassays were conducted in stored grains to determine the toxicity of powders of Eugenia aromatica and Moringa oleifera alone or combined with enhanced diatomaceous earth (Probe-A® DE, 89.0% SiO2 and 5% silica aerogel) to adult Sitophilus granarius, Tribolium castaneum and Acanthoscelides obtectus. Adult mortality was observed up to 7 days, while progeny productionwas recorded at 6–10 weeks. LD50 and LT50 values for adult test insects exposed to plant powders and DE, showed that A. obtectus was the most susceptible towards the botanicals (LD50 0.179% and 0.088% wt/wt for E. aromatica and M. oleifera, respectively), followed by S. granarius. Tribolium castaneum was most tolerant (LD50 1.42% wt/wt and 1.40% wt/wt for E. aromatica and M. oleifera, respectively). The combined mixture of plant powders and DE controlled the beetles faster compared to the plant powders alone. LT50 ranged from 55.7 h to 62.5 h for T. castaneum exposed to 1.0% M. oleifera and 1.0% DE, and 0.5% E. aromatica and 1.0% DE, respectively. Botanicals caused significant reduction of F1 adults compared to the control. Combined action of botanical insecticides with DE as a grain protectant in an integrated pest management approach is discussed.