Development of handling and transport protocols for Eldana saccharina (Lepidoptera: Pyralidae) sterile insect technique (SIT) programme

Thesis (MScConsEcol)--Stellenbosch University, 2021.ENGLISH ABSTRACT: Eldana saccharina Walker (Lepidoptera: Pyralidae), is indigenous to sub-Saharan Africa and is a serious economical pest of sugarcane in South Africa. Recent area-wide integrated pest management (AW-IPM) efforts have proven to be effective in lowering infestations and better predicting population growth and spread into new areas. The sterile insect technique (SIT) promises to provide great benefit as a component of the AW-IPM strategy. This study aimed to establish parameters for collection, packaging, and transport of recently emerged E. saccharina adult males, within a maintained cold chain conjointly with methodologies for the routine assessment of the performance and competitiveness of sterilized insects. These treatments should not impact the fitness nor mating ability of the adults exposed to them. Several major outcomes were realized, summarized as follows: Parental male and female pairs exposed to 100 Gy irradiation prior to mating provided an 83.3 % male biased first filial generation. Thus, a male biased, semi sterile generation could be reared for collection and release using this technique; difference between average male (0.0700 g) and female (0.133 g) pupal weights (as an indication of adult weight) were identified as a morphological trait that could be exploited to obtain a high degree of sex separation; and the plenum collection box was effective in collecting male and female adult E. saccharina (a mean of 80.67 % ± 4.56 % adults were collected when placing 200 adult moths (male : female = 1:1) into the prototype collection system overnight for 12 hours replicated three times). Furthermore, the effect of exposure of virgin E. saccharina males to 5 °C for 24, 48 and 72 hours on male mating frequency and longevity was measured to determine the impact of prolonged periods of cold exposure to male fitness. The 72 hour treatment showed a significant decrease in male mating frequency (average of 4.4 females mated at 48 h versus 2.7 females mated at 72 hours). It is therefore possible to hold E. saccharina at 5 °C for 48-hours without impacting on moth fitness in terms of mating frequency. Bran was identified as a good temperature insulating material to use as a packaging substrate for adult males, as it buffered temperature fluctuations over time inside a transportable freezer set at 5 °C (1.5 °C to 5.5 °C) when fully stocked with bran, versus being empty (0 °C to 6 °C). Bran’s effect as a packaging substrate on male fitness during high density packaging and exposure to 5 °C for 24, 48 and 72 hours showed no significant decrease in male mating frequency (mean mating frequency of 2.8889 females mated). Males did have a decreased mating frequency (1.4667 females mated) after 72 hours for the no bran packaged adults. A visual rating system was tested to measure the difference in loose scale cover - on the eyes, dorsal surface, ventral surface, as well as scale loss from the pronotum - between bran and no bran packaged moths. There was a clear improved visual quality with bran packaged adults compared to no bran packaged adults with less scale loss from the pronotum and less loose scales covering the eyes and ventral and dorsal surfaces, indicating that this visual rating system could be valuable as a quality control check at the point of elease.AFRIKAANSE OPSOMMING: Eldana saccharina Walker (Lepidoptera: Pyralidae), is inheems aan Suider Afrika en is 'n ernstige ekonomiese plaag op suikerriet in Suid-Afrika. Onlangse pogings tot area wye geïntegreerde plaag bestuur was effektief. Die steriele insek tegniek (SIT) beloof om 'n groot voordeel te lewer as komponent van die area wye strategie tot beheer. Die produksie van E. saccharina kan voortdurende produksie volumes van mededingende motte verseker. 'n Stralingsdosis van 200 Gy het geen invloed op die paringsgedrag of die algemene fiksheid van volwasse motte nie en laat mannetjies gedeeltelik steriel vir gebruik in ‘n SIT program. Hierdie studie poog om parameters vas te stel vir versameling, verpakking en vervoer binne 'n onderhoude koue ketting, tesame met metodieke vir die roetine-assessering van die mededingendheid van gesteriliseerde insekte. Die blootstelling van mannetjie en wyfie ouer-pare aan bestraling van 100Gy voor paring het 'n 83,3% mannetjie opeenvolhende generasie gegee. Die meerderheid mannetjie, semi-steriele generasie kan dus groot gemaak word vir versameling en vrylating. Verskil tussen mannetjie en vroulike mot gewigte is geïdentifiseer as 'n morfologiese eienskap wat gebruik kan word om 'n sterk mate van skeiding te verkry. Die plenum-versamelingskis is effektief vir die versameling van mannetjie en wyfie E. saccharina. Deur motte bloot te stel aan koue temperature vir hoë digtheid verpakking vir bestraling, vervoer tot met vrylating verhoed dit dat liggaamlike aktiwiteit mot fiksheid sal beskadig. 'n Immobiliseer- en houtemperatuur van 5 °C is gebruik wat bo die motte se kritieke minimum temperatuur van 4,4 °C is. Die effek van blootstelling van maagdelike E. saccharina mannetjies aan 5 °C vir 24, 48 en 72 uur op mannetjie parings frekwensie en langlewendheid is gemeet om die impak van langdurige periodes van koue blootstelling aan mannetjie fiksheid te ondersoek. Die 72 uur behandeling het 'n beduidende afname in die parings frekwensie vir mannetjies getoon in vergelyking met alle ander behandelings. Dit is dus moontlik om E. saccharina by 5 °C te hou vir tot 48 uur sonder om die motfiksheid in terme van parings frekwensie te beïnvloed. Semels is geïdentifiseer as 'n goeie temperatuur isolerende buffer om as verpakkingssubstraat te gebruik, en het dus ook getoon dat temperatuurswisseling verminder as die temperatuur met verloop van tyd binne die vervoerbare vrieskas gemeet word wanneer dit vol met semels is teenoor om leeg te wees. Semels se effek as verpakkingssubstraat op mannetjie fiksheid tydens hoë digtheid verpakking en blootstelling aan 5 °C gedurende 24, 48 en 72 uur het geen beduidende afname in mannetjieparings frekwensie getoon nie. Mannetjies het wel na 72 uur 'n verlaagde parings frekwensie gehad vir die nie-semels verpakte motte. 'n Visuele waarderingstelsel is getoets om die verskil in losskaal bedekking aan die oë, rugkant, ventrale kant sowel as skaal verlies te meet aan die pronotum tussen semels en geen semels verpakte motte. Daar was 'n duidelike verbeterde visuele kwaliteit met semels verpakte motte in vergelyking met geen semels verpakte motte , wat daarop dui dat hierdie visuele waarderingstelsel waardevol kan wees as 'n gehaltebeheer op die punt van vrylating.Master