Quantifying the impacts of cactus biological control agents in South Africa - Mnqeta, Zezethu (Rhodes University, Faculty of Science, Department of Zoology and Entomology)
Invasive alien cacti are prominent weeds that threaten indigenous biodiversity and have a negative impact on agricultural productivity in South Africa. These plants are problematic because they form dense thickets that reduce the carrying capacity of rangelands; restrict the movement of livestock and wildlife thus reducing access to shade and water sources; and are directly harmful to livestock, wildlife and people due to their sharp spines. Biological control is the most effective, affordable and environmentally friendly method to control invasive alien cacti and minimize their negative impacts. Cochineal insects (Dactylopius spp.: Dactylopiidae) and the gall-forming mealybug, Hypogeococcus sp. (Pseudococcidae) are used as biological control agents for cacti. The agents are however poor dispersers, so mass-rearing and augmentative releases are required in order to establish the agents at sites where they are needed. This study aimed to evaluate the mass-rearing and release efforts of cactus biological control in South Africa, quantify the impact of the biological control agents on cactus plant populations through long-term monitoring, and assess the benefits accrued due to the biological control agents through the perceptions of land-users. An assessment of the effectiveness of the release effort for cactus biological control agents was conducted by comparing where biological control agents have been released with the known distribution of the target weeds. Only 26% of the quarter degree squares that are known to be occupied by invasive alien cacti have had biological control agents released in them. This indicated that the mass-rearing and release efforts in South Africa are inadequate and should be increased, especially in areas where few releases have been made and many cacti are present, such as the Limpopo Province. The impact of the biological control agents on cactus plant populations was assessed by monitoring agent densities, target plant densities and target plant reproductive outputs before and after releases. Plant biomass and reproductive output were reduced by biological control agents for three of the target weeds that were assessed, while the duration of the study was too short to measure reductions for the fourth target weed. Benefits to land-users were then quantified through a questionnaire survey. Land-users perceived biological control as an effective management option, with 81% of the land-users reporting that there was less invasive alien cactus after releasing biological control agents on their land. Forty-nine percent of the land-users believed that the negative impacts of the cactus had been reduced and that they benefited more from their land since control was achieved. Since land-users were only interviewed within four years of the releases being conducted, it is expected that the percentage of land-users who gained benefits from biological control will increase in future. Ninety-seven percent of the land-users stated that the agents were safe and had not fed on any other plants or had any detrimental impacts. These perceptions indicated that land-users regarded biological control as a safe and effective method of controlling invasive alien cacti. This study confirms that biological control is an effective and safe way of controlling invasive alien Cactaceae. It is also the first to assess some of the benefits that land-users have accrued due to biological control of cactus weeds. It is however evident that a greater mass-rearing and release effort is required for South Africa to get the maximum benefits possible from the use of the biological control agents for cactus weeds that are available in the country.,Izityalo ze-cactus ezisuka kwamanye amazwe zilukhula olubalaseleyo, olwenza ingxaki kwintlobo ngeentlobo zezityalo nezilwanyana kwaye ezizityalo zinefuthe neziphumo ezingalunganga kwimveliso yezolimo eMzantsi Afrika. Ezi zizityalo ziyingxaki kuba zenza amatyholo ashinyeneyo athi anciphise umthamo wokusebenzisa umhlaba: zinqanda ukuhamba nogkukhululekileyo kwemfuyo nezilwanyana zasendle ngokwenza oko zingakwazi ukufikelela emthuzini xa kutshisa nakwimithombo yamanzi yokusela; zikwayiyo nengozi kwimfuyo, izilwanyana zasendle kunye nabantu ngenxa yamave abukhali afumaneka kwezizityalo. Ukulawula nokwehliza ubunzini nezinga lemigcipheko yezizityalo, kusetyenziswa indlela ekuthiwa yi-biological control. Lendlela yeyona ndlela isebenza ngokuphucukileyo, efikelelayo, nengenabungozi kokusingqongileyo. Izinambuzane ze- cochineal (i-Dactylopius spp.: Dactylopiidae) kunye ne-mealybug, i-Hypogeococcus sp. (Pseudococcidae) zisetyenziswe njengezixhobo ze-biological control ezinceda ukulawula ezizityalo ze-cactus zingafunekiyo. Ingxaki yazo ezizinambuzane zizixhobo ze-biological control zingentla kukuba azikwazi kuzisasaza ngokwazo ukuba zifikelele nakwizityalo ezikude ngoko ke ukukhuliswa nokukhutshwa ngobuninzi bazo kuyafuneka ukukhawulelana nalengxaki kunye nokwandisa amathuba wokuba zifikelele kuzozonke izityalo ze-cactus ekufuneka zizilawule. Olu phononongo lujolise ekuvavanyeni iinzame zokukhulisa ngobuninzi nokukhupha ezezinambuzane zizixhobo ze-bioloigical control zokulawula izityalo ze-cactus eMzantsi Afrika, ukujonga ubungakanani befuthe notshintsho elenziwa zezinambuzane zizixhobo ze-bioloigical control kwizityalo ze-cactus emva kwexesha elide lokuzijonga, kunye nokuvavanya inzuzo efunyenwe ngenxa yokulawula ezizityalo ze-cactus ngokwemibono yabasebenzisi bomhlaba. Uvavanyo lweenzame zokukhutshwa kwezixhobo zezixhobo zezinambuzane ze-bioloigical control kwizityalo ze-cactus lwenziwa ngokuthelekisa iindawo apho izixhobo zezinambuzane ze-biological control zikhutshwe khona kunye neendawo apho izityalo ze-cactus kwaziwayo ukuba ziyafumaneka khona. Yi-26% kuphela yesikwere sekota eyaziwayo ukuba kukhona izityalo ze-cactus nalapho kukhutshwe khona kwezinambuzane ezizixhobo ze-biological control. Oku kubonisa ukuba iinzame zokukhulisa nokukhutshwa kwezinambuzane ezizixhobo ze-biological control eMzantsi Afrika azanelanga kwaye kufuneka zandiswe, ngakumbi kwiindawo apho kukho ukhutsho olumbalwa olwenziweyo kunye nezityalo ze-cactus ezininzi ezifumaneka khona, njengePhondo laseLimpopo. Iimpembelelo yokukhutshwa kwezinambuzane ezizixhobo ze-biological control kwizityalo ze-cactus zavavanywa ngokujonga ubunizi bezinambuzane ezizixhobo ze-biological control, ukuxinana kwezityalo ze-cactus ekujoliswe kuzo kunye nemveliso yokuzala kwezityalo ze-cactus phambi nasemva kokuba kukhutshwe izinambuzane ezizixhobo ze-biological control. Ubungakanani bezityalo ze-cactus kunye nemveliso yokuzala ziye zacutheka emva kokukhutshwa kwezinambuzane ezizixhobo ze-biological control kwinzityalo ezintathu ze-cactus ebekujoliswe uvavanyo kuzo, ngelixa ixesha lophononongo lalifutshane kakhulu ukuvavanya unciphiso kwisityalo se-cactus sesine. Izibonelelo zabasebenzisi bomhlaba zaye zavavanywa kusetyenziswa uhlobo lwemibuzo. Abasebenzisi bomhlaba balubona ukusetyenziswa kwezinambuzane ezizixhobo ze-biological control njengendlela yolawulo olusebenzayo, yi81% yabasebenzisi bomhlaba echaze ukuba izityalo ze-cactus zecuthekile emva kokukhutshwa kwezinambuzane ezizixhobo ze-biological control emhlabeni wabo. Amashumi amane anesithoba eepesenti zabasebenzisi bomhlaba bakholelwa ukuba impembelelo ezingalunganga ze-cactus zincitshisiwe kwaye baxhamle kakhulu kumhlaba wabo okoko lwaphunyenzwa. Oludliwano-ndlebe belwenziwe kubasebenzisi bomhlaba kwisithuba seminyaka emine emva kokuba kukhutshwe izinambuzane ezizixhobo ze-biological control, kulindeleke ukuba ipesenti yabasebenzisi bomhlaba abathe bafumana izibonelelo kwi-biological control lonyuke kwixesha elizayo. Amashumi alithoba anesixhenxe ekhulwini abasebenzisi bomhlaba bachaze ukuba izinambuzane ezizixhobo ze-biological control zikhuselekile kwaye khange zidle kuzo naziphi na ezinye izityalo ezingezi eze-cactus ebekujoliswe kuzo okanye zineempembelelo eyingozi. Ezi mbono ziyabonisa ukuba abasebenzi bomhlaba bayithatha i-biological control njengendlela ekhuselekileyo nesebenzayo yokulawula izityalo ze-cactus zamanye amazwe. Olu phononongo luqinisekisa ukuba ulawulo olusebenzisa izinambuzane ezizixhobo ze-biological control yindlela esebenzayo nekhuselekileyo yokulawula iCactaceae yamanye amazwe. Ikwangolokuqala ukuvavanya ezinye zezibonelelo ezizuzwe ngabasebenzisi bomhlaba ngenxa ye-biological control yezityalo ze-cactus. Nangona kunjalo kucacile ukuba ukwandisa inzame zokukhulisa nokukhupha ngobuninzi izinambuzane ezizixhobo ze-biological control kuyafuneka ukuze uMzantsi Afrika ufumane izibonelelo eziphakamileyo enokubakho ngokusetyenziswa kwe zinambuzane ezizixhobo ze-biological control zokulawula ukhula lwe-cactus olukhoyo kweli lizwe.,Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
Keywords: Cactus Biological control -- South Africa; Noxious weeds -- South Africa; Invasive plants Biological control -- South Africa; Insects as biological pest control agents -- South Africa; Cochineal insect -- South Africa; Mealybugs -- South Africa; Agricultural productivity -- South Africa