Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae) i Benin : artens egenskaper for biologisk kontroll av bladlus i grønnsaksystemer

In Benin, vegetable producers’ reliance on toxic synthetic pesticides threatens the environment and human health. However, the recent discovery of Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae) in Benin offers new options for integrated pest management (IPM), particularly with a view to biological control of aphid host pest species in vegetable agroecosystems in the country. The current work therefore discusses the potential of the alien parasitoid L. testaceipes to control aphids within the framework of integrated pest management. The results demonstrate that the wasp increases its stabbings in order to increase the chance of oviposition on Aphis gossypii Glover and Aphis craccivora Koch (Homoptera: Aphididae). Aphis craccivora and especially fourth instars exhibited more intensive defense behavior against L. testaceipes compared to second instar-nymphs. The data proved that energy (honey as sustenance) had a significant effect on the wasp's oviposition performance, compared to that observed in females supplied with water. A single sting of L. testaceipes was sufficient to induce successful parasitism on its hosts, although the rate for achieving this was low. The wasp performed less than four stings on aphids younger than third instar prior to oviposition. These stabbings were increased to around seven stings on older nymphs. This was to counter stronger aphid defense and therefore increase the probability of successful oviposition. Parasitism negatively affected the survival and fertility of A. gossypii. The life-time fecundity of the aphid at third instar decreased dramatically to 4.66 times (only 7.569 ± 2.381 nymphs per female) as a result of parasitism by L. testaceipes. A decrease of 7.33 and 2.45 times of the net reproductive rate (2.119 ± 0.272) and the intrinsic rate of increase (0.110 ± 0.018), respectively, was also observed among parasitized aphids. Furthermore, the wasp displayed a type II functional response on A. gossypii in the laboratory at 26 ± 1ºC. Field trials proved that the wasp is effective in aphid suppression, despite the fact that the attack of the indigenous hyperparasitoid Syrphophagus africanus (Gahan) (Hymenoptera: Encyrtidae) was observed. In addition, investigation in the field during both rainy and dry seasons, in 2011 and 2012 respectively, showed that the parasitoid along with three native predatory species that feed on aphids Cheilomenes propinqua (Mulsant), Cheilomenes sulphurea (Olivier) (Coleoptera: Coccinellidae) and Ischiodon aegyptius (Wiedemann) (Diptera: Syrphidae) responded positively in numerical terms to changing densities of A. gossypii. Laboratory work carried out at 26 ± 1ºC provided evidence that the three recorded predators are potential competitors to L. testaceipes. The three native predatory species had substantial consumption rates of A. gossypii, the aphidophagous larvae of I. aegyptius being the most voracious compared to their corresponding instars of the ladybirds C. propinqua and C. sulphurea. Daily consumption of unparasitized aphids by first instars of predators was 9.58 ± 2.89; 12.03 ± 4.36 and 17.40 ± 7.18 for C. propinqua, C. sulphurea and I. aegyptius, respectively. The consumption rate increased 7.99 and 7.38 times for fourth instars C. propinqua and C. sulphurea, respectively; and 5.00 times for third instar I. aegyptius. The results also indicate that the predators provide an important ecosystem service regarding the natural control of the aphid. However, the data revealed an existence of asymmetrical omnivorous intraguild predation of A. gossypii mummies parasitized by L. testaceipes, by C. propinqua and C. sulphurea. Fourth instar of C. sulphurea was the most destructive omnivorous intraguild predator. They killed 46.06% of L. testaceipes pupae within 24 hours. In contrast, I. aegyptius larvae did not attack the aphid mummies parasitized by L. testaceipes. These findings indicate that the intraguild interactions between the alien parasitoid L. testaceipes and indigenous aphid predators probably play an important role in determining community structure, and they also act as regulators of both the aphid populations and the alien wasp populations. In conclusion, the study's results demonstrate that L. testaceipes is a promising biocontrol agent for the two major vegetable aphid pests A. gossypii and A. craccivora and this insight provides important background information for sound decision-making with regard to implementing sustainable measures for aphid management in Benin.Grønnsakprodusenter i Benin er avhengig av å bruke syntetiske pesticider, noe som utgjør en risiko for både miljø og helse. Bladlussnyltevepesen Lysiphlebus testaceipes (Cresoon) (Hymenoptera: Braconidae, Aphidiinae) ble nylig oppdaget i Benin, og dette kan gi nye muligheter for integrert plantevern (IPM), særlig med tanke på biologisk kontroll av bladlus i ulike grønnsaksystemer. Dette doktorgradsarbeidet diskuterer derfor hvilket potensiale den fremmede arten L. testaceipes har for å holde bladlus under kontroll innenfor rammene av en IPM strategi. Resultatene viser at snyltevepsen intensiverer angrepene (antall stikk) med den hensikt å øke mulighetene for egglegging i Aphis gossypii Glover og Aphis craccivora Koch (Homoptera: Aphididae). Aphis craccivora, og da særlig det fjerde nymfestadium viste en mer intens forsvarsadferd sammenlignet med andre nymfestadium. Forsøkene har vist at energi (honning-løsning) førte til en signifikant økning i egglegging, sammenlignet med hunner som ble foret med bare vann. Ett enkelt stikk med eggleggingsbrodden var nok til å parasittere en vert, men sannsynligheten for vellykket parasittering var liten med bare ett stikk. Snyltevepsen brukte mindre enn fire stikk med brodden på nymfer yngre enn tredje stadium, men måtte øke frekvensen til rundt sju stikk på eldre nymfer. Denne endringen i adferd skyldes at snyltevepsen måtte bekjempe den økende motstanden som eldre nymfer/bladlus gir i forhold til unge nymfer for å lykkes med eggleggingen. Parasitterte bladlus hadde dårligere overlevelse og nedsatt fertilitet sammenlignet med uparasitterte. Den totale fertiliteten (livsløpsfertiliteten) hos bladlus parasittert av L. testaceipes i tredje nymfestadium ble redusert med 4,66 ganger (kun 7,569 ± 2,381 nymfer per hunn). Netto reproduksjon ble redusert med 7,33 ganger (2,119 ± 0,272), mens populasjonsveksten (intrinsic rate of increase) ble redusert 2,45 ganger (0,110 ± 0,018) hos parasitterte bladlus. I laboratorieforsøk viste snyltevepsen type II funksjonell respons til A. gossypii ved 26 ± 1°C. Feltforsøk viste at snyltevepsen er effektiv som bladlus regulator til tross for at angrep fra den innfødte hyperparasitten Syrphophagus africanus (Gahan) (Hymenoptera: Encyrtidae) ble observert under naturlige forhold. I tillegg viste feltforsøk gjennomført både i regntida og i tørketida i henholdsvis 2011 og 2012, at snyltevepsen og de tre innfødte bladlus predatorene Cheilomenes propinqua (Mulsant), Cheilomenes sulphurea (Olivier) (Coleoptera: Coccinellidae) og Ishiodion aegyptius (Wiedemann) (Diptera: Syrphidae) reagerte positivt i antall til ulike tettheter av A. gossypii. Forsøk utført i laboratoriet (26 ± 1°C) viste at disse tre predatorene er potensielle konkurrenter til L. testaceipes. Alle de tre innfødte predatorene konsumerte A. gossypii i betydelige mengder, der larvene av I. aegyptius spiste mest sammenlignet med tilsvarende larvestadier av de to marihønene C. propinqua og C. sulphurea. Daglig konsum av uparasitterte bladlus for første larvestadium av de tre predatorene var 9,58 ± 2,89; 12,03 ± 4,36 og 17,40 ± 7,18 for henholdsvis C. propinqua, C. sulphurea og I. aegyptius. Konsumraten økte med 7,99 og 7,38 ganger for fjerde larvestadium av henholdsvis C. propinqua og C. sulphurea, og 5,00 ganger for tredje larvestadium av I. aegyptius. Resultatene viser at predatorene er viktige i økosystemet med hensyn på naturlig regulering av bladluspopulasjoner. Forsøkene avslørte en asymmetrisk omnivor intraguild predasjon på mummier av A. gossypii parasittert av L. testaceipes. Fjerde larvestadium av C. sulphurea var den mest ødeleggende omnivore intraguild predatoren, og drepte 46,6% av puppene av L. testaceipes i løpet av 24 timer. Larvene av I. aegyptius derimot angrep ikke bladlusmummier parasittert av L. testaceipes. Disse resultatene indikerer at intraguilde interaksjoner mellom den fremmede arten L. testaceipes og innfødte predatorer sannsynligvis spiller en viktig rolle når det gjelder artsstrukturen i/formingen av økosystemet, og at disse samspillene også fungerer som regulatorer av både bladluspopulasjonen og populasjonen av den fremmede snyltevepsarten. For å konkludere, resultatene viser at L. testaceipes er en lovende organisme for biologisk kontroll av de to viktigste bladlusartene i grønnsaker, A. gossypii og A. craccivora. Dette er viktig basiskunnskap for å utvikle og implementere bærekraftige kontrollmekanismer for bladlus i Benin.Norges Forskningsrå

Four AICCRA-Ghana partners are using project-generated climate information services to support farmer resilience to climatic shocks| Outcome Impact Case Report (OICR) for PDO 1

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