Papers by Hannalene Du Plessis
African Crop Science Journal, 1997
(African Crop Science Journal, 1997 5(1): 47-54
Biocontrol Science and Technology, 2018
Tuta absoluta is an alien invasive pest in Sudan. Since it was detected in the country, the pest ... more Tuta absoluta is an alien invasive pest in Sudan. Since it was detected in the country, the pest continues to cause major tomato losses. Alarmed by its devastating nature and the speed of spread, tomato growers resorted to the indiscriminate use of broad-spectrum insecticides. Promising indigenous parasitoid(s) may contribute to suppression of this pest. The biology and performance of the native parasitoids, Bracon nigricans Szépligeti (Braconidae) and Dolichogenidea appellator (Telenga) (Braconidae), was therefore evaluated against different immature stages of T. absoluta under laboratory conditions. A significantly higher number of fourth instar larvae was accepted for oviposition by B. nigricans. Similarly, fourth instar larvae yielded a considerably higher number of parasitoid offspring compared to third instar larvae. The male ratio of B. nigricans offspring which emerged from both larval instars was high, 0.96 and 0.66 for third and fourth instar larvae of T. absoluta, respectively. There was, however, no significant difference in the number of males and females that emerged from fourth instar larvae. Conversely, the number of hosts killed by stinging behaviour or host feeding was significantly higher on third instar larvae. B. nigricans potential fecundity varied with the age of the wasp with the lowest fecundity on the day of eclosion. The performance of D. appellator in terms of the total number of offspring produced and female progeny was similar for second and third instar larvae of T. absoluta. The preimaginal developmental time for both parasitoid species did not vary with either host stage or sex of the parasitoid. B. nigricans adult longevity was similar for both sexes, while that of D. appellator significantly varied with females living longer than males. Prospects for conservative biological control of T. absoluta are discussed in the light of the results of this study.
... Hilda infests 2-5% groundnut plants in most countries of southern Africa during the normal gr... more ... Hilda infests 2-5% groundnut plants in most countries of southern Africa during the normal growing seasons, but extensive damage (up to 80%) has been observed in some groundnut fields during prolonged dry spells or in off-season crops (Weaving 1980, Minja et al. 1999). ...
Bulletin of entomological research, 2017
The effect of temperature on the reproduction and development of Busseola fusca was studied under... more The effect of temperature on the reproduction and development of Busseola fusca was studied under laboratory conditions. Single male-female pairs were confined to oviposition chambers kept at 15, 20, 26 and 30 ± 1°C and a 14L:10D photoperiod. Data on reproduction parameters were captured daily. Oviposition occurred at all the mentioned temperatures but no fertility was recorded at 30°C. The total number of eggs laid per female moth was between 300 and 400 and the optimum temperature for oviposition and fertility was between 20 and 26°C. Larval development was studied at five different temperature regimes, i.e. 15, 18, 20, 26 and 30 ± 1°C and a 14L:10D photoperiod. The most favourable temperature as well as the upper threshold temperature for larval development was between 26 and 30°C. Total development period was 152.6-52.6 days, respectively, at 15°C, and 26-30°C. The thermal constants for B. fusca was 99.50, 536.48, 246.25 and 893.66°D and lower temperature thresholds were 10.36, ...
South African Journal of Plant and Soil, 2003
The groundnut leafminer, Aproaerema modicella is an important pest of groundnut and soybean in So... more The groundnut leafminer, Aproaerema modicella is an important pest of groundnut and soybean in South and South-East Asia. It has also been reported from Uganda, Malawi and Mozambique. During 2000, it was first noticed on groundnut in South Africa. Since then it has spread over the entire groundnut production area of the Free State, Northern Cape, North West and Mpumalanga provinces. Reduction in yield was observed under conditions of severe infestations. During 2001 A. modicella was also observed on soybean in Mpumalanga and lucerne in the Northern Cape province, respectively.
bioRxiv (Cold Spring Harbor Laboratory), Jun 10, 2019
The invasive fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) is a polyphagous pest that c... more The invasive fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) is a polyphagous pest that causes widespread damage particularly to maize and sorghum in Africa. The microbiome associated with S. frugiperda could play a role in their success and adaptability. However, these bacterial communities remain poorly studied, especially for S. frugiperda in Africa. We investigated the composition, abundance and diversity of microbiomes associated with larval and adult specimens of S. frugiperda collected from four maize growing regions in Kenya through high throughput sequencing of bacterial 16S rRNA gene. We identified Proteobacteria and Firmicutes as the most dominant phyla and lesser proportions of Bacteroidetes and Actinobacteria. We also observed differences in bacterial microbiome diversity between larvae and adults that are a likely indication that some prominent larval bacterial groups are lost during metamorphosis. Several bacterial groups were found in both adults and larvae suggesting that they are transmitted across developmental stages. Reads corresponding to several known entomopathogenic bacterial clades as well as the non-bacterial entomopathogen, Metarhizium rileyi (Farl.) Kepler, Rehner & Humber (2014), were observed. Mitochondrial DNA haplotyping of the S. frugiperda population in Kenya indicated the presence of both 'Rice' and 'Corn' strains, with a higher prevalence of the 'Rice' strain. Insights into the microbiota may ultimately provide alternative avenues for controlling of this pest.
Agriculture, Aug 30, 2021
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Journal of Economic Entomology, Oct 12, 2018
Transgenic Bt maize expressing Cry insecticidal δ-endotoxins of Bacillus thuringiensis has been c... more Transgenic Bt maize expressing Cry insecticidal δ-endotoxins of Bacillus thuringiensis has been cultivated in South Africa for the control of Busseola fusca since 1998. Busseola fusca is resistant to Cry1Ab Bt maize at many localities throughout the maize production region. Pre-release evaluation (1994-1996) of the inherent susceptibility and postrelease assessments (1998-2011) of resistance status of B. fusca focused on a limited number of pest populations. This study reports the current levels of susceptibility of 10 B. fusca populations evaluated between 2013 and 2017 and compared this data with previously reported data on the survival of this pest on Bt maize, including data of pre-release evaluations done during 1994 and 1995. Larval feeding bioassays in which plant tissue of maize events expressing either Cry1Ab or Cry1A.105+Cry2Ab2 (stacked event) proteins were conducted and survival and different life history parameters recorded. Results show a shift in levels of susceptibility of B. fusca to Bt maize. Pre-release evaluation of the single-gene event showed very low larval survival on Bt maize leaf tissue while studies 10 yr later and the current study reported survival of up to 40% and 100% on Cry1Ab maize, respectively. While no larvae completed their life cycle on the stacked event, higher LT50 values in this study indicate a shift in susceptibility of B. fusca to the stacked-gene event and highlight the importance of baseline information and monitoring of pest populations for their susceptibility to Bt maize.
African Entomology, Nov 1, 2022
Limited information is available regarding the distribution of the African mantis, Sphodromantis ... more Limited information is available regarding the distribution of the African mantis, Sphodromantis gastrica (Stål) (Mantodea: Mantidae) and no information is available on its biology. The aim of this study was to determine the distribution of S. gastrica in South Africa based on historic insect collection records and citizen science platforms occurrence data, and to study its basic biology and developmental parameters under captive breeding conditions. A total of 153 South African museum records of Sphodromantis spp. were recorded during this study, while 39 Research Grade observations from iNaturalist were also included. These records indicated that S. gastrica occurred in all provinces of South Africa. The incubation time of the S. gastrica oothecae were approximately 10 weeks and each ootheca contained an average of 84 egg chambers. The mean fertility rate was 54.6% while the survival rate until adulthood was 41.8%. The mean lifespan of S. gastrica individuals were approximately 332 days and females lived longer than males. This study will provide a baseline as it is the first published data on the distribution and biology of this common and charismatic insect in South Africa.
African Entomology, Sep 1, 2017
Earias biplaga (Walker) (Lepidoptera: Noctuidae) forms part of the bollworm pest complex of cotto... more Earias biplaga (Walker) (Lepidoptera: Noctuidae) forms part of the bollworm pest complex of cotton in South Africa. Genetically modified Bt cotton that expresses Cry insecticidal proteins successfully controls the bollworm complex in South Africa. Although many insecticides are registered for use against Lepidoptera on this crop, Bt sprays are not registered for control of E. biplaga. The aim of this study was to determine the efficacy of Bacillus thuringiensis spray applications for the control of E. biplaga on non-Bt cotton and to compare the efficacy of sprays to that provided by Bt cotton. Bioassays were conducted in which cotton bolls of a non-Bt cotton cultivar (Delta Opal) were sprayed with different dosage rates of Dipel DF®, which contains the following insecticidal proteins: Cry1Aa, Cry1Ab, Cry1Ac, Cry2Aa and Cry2Ab. Bollgard® and Bollgard II® cotton which expresses Cry1Ac and both Cry 1Ac and Cry2Ab were used in the study. Neonate larvae were inoculated onto cotton bolls and survival observed 4, 7 and 10 days later. The Bt spray dosage rate recommended for control of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on groundnut and sunflower in South Africa was used in this study and provided between 77 and 88%control of E. biplaga after 10 days. Bt cotton provided 100%control after 10 days. This study provides baseline data on the susceptibility of E. biplaga against Bt cotton which can also be used for future monitoring of resistance evolution.
Crop Protection, 2009
... A. van der Walt a , H. du Plessis b and J. Van den Berg a , Corresponding Author Contact Info... more ... A. van der Walt a , H. du Plessis b and J. Van den Berg a , Corresponding Author Contact Information , E-mail The Corresponding Author. ... Previous studies only reported on the number of larvae per plant ([Muthiah and Kareem, 2000] and [Kenis and Cugala, 2006]). ...
Insects, Feb 11, 2020
Galepsus Stäl is a genus within the Mantodea and has hardly been studied in Africa. The distribut... more Galepsus Stäl is a genus within the Mantodea and has hardly been studied in Africa. The distribution of the Galepsus genus in Southern Africa was established, based on insect collection records, and the biology of Galepsus (Lygdamia) lenticularis Saussure, was studied. In Southern Africa, 11 species of Galepsus were recorded. The first record of Galepsus (Onychogalepsus) centralis Beier, in South Africa was recorded during this study. The mean number of eggs per ootheca was 49.8 (±21.1) and unfertilized oothecae were significantly shorter and contained fewer eggs than hatched and unhatched oothecae, suggesting that females might invest fewer resources into production of oothecae that will not produce prodigy. No parthenogenesis was observed during this study. Although the mean duration of the male and female nymphal stages were similar, longevity of adult females (91.2 ± 35.0 days) was three times longer than that of males (26.3 ± 15.4 days). This phenomenon as well as the long period (20 ± 14.1 days) between oviposition of different oothecae, and duration of the incubation period (20.25 ± 6.3 days) suggests a survival strategy to reduce competition between siblings. Total longevity of males (166.9 ± 38.8) and females (252.9 ± 54.2) differed significantly. This study provides information on the distribution of Galepsus spp. in Southern Africa and describes the biology of G. lenticularis under captive breeding conditions, and contributes to the understanding of various biological aspects of G. lenticularis which has never been studied before.
African Entomology, Mar 1, 2017
African Entomology, Sep 1, 2007
Feeding by Nysius natalensis (Hemiptera: Orsillidae) adults on sunflower heads reduces grain yiel... more Feeding by Nysius natalensis (Hemiptera: Orsillidae) adults on sunflower heads reduces grain yield, oil content and seed germination. Since the insect is known to feed on several host plants, a study was conducted on its host plant range to assess the role that weeds played in the pest status of this insect throughout the sunflower production area of South Africa. Roadside surveys of hosts, conducted in every quarter-degree grid of the sunflower production area, showed that N. natalensis was ubiquitous. The insect survived, developed and reproduced across a wide range of temperature and rainfall conditions. Feeding of nymphs and adults, as well as the presence of eggs was observed on 26 plant species belonging to eight families. The polyphagous habits of N. natalensis, together with a favourable temperature range for development in its distribution area, are important factors in determining population density of the pest. Late-planted sunflowers were prone to N. natalensis damage because seed-fill coincided with high numbers of the insect that increased during spring and summer. These individuals migrated onto sunflower with senescence of host weeds prior to winter. Recommendations are made on weed management practices to limit damage by N. natalensis.
Entomologia Experimentalis Et Applicata, Oct 11, 2012
Nysius natalensis Evans (Hemiptera: Orsillidae) is a pest of sunflower in South Africa. Adults in... more Nysius natalensis Evans (Hemiptera: Orsillidae) is a pest of sunflower in South Africa. Adults invade sunflower fields from their weedy hosts which occur inside crop fields and on surrounding headlands. The host plant suitability for survival and reproduction as well as the effect of withingeneration host switching was studied on different wild host plants and sunflower. Life history parameters used to assess host plant suitability were F 1 adult survival, pre-oviposition period, fecundity, and longevity. Nymphs and adults were provided with stems and seeds of five host plants, viz., Amaranthus hybridus L. (Amaranthaceae), Portulaca oleracea L. (Portulacaceae), Chenopodium album L. (Chenopodiaceae), Conyza albida Spreng. (Asteraceae), and sunflower, Helianthus annuus L. (Asteraceae). Nymphs were reared on crushed seed of the five plant species. After completion of the nymphal stage, emerging adults of each host plant group were provided with seed of a different host plant species for food. Adults did not survive long on stems only and very few eggs were laid. Seeds of the host plant species were shown to be an essential source of nutrients for N. natalensis reproduction, whereas the vegetative plant parts were unsuitable. Nymphal food and host-plant switching between the nymphal and adult stages significantly affected the pre-oviposition period. Nymphal and adult food source also affected female longevity. The number of eggs laid was not influenced by nymphal food, but was influenced by adult food and the switch between nymphal and adult food. The comparative attractiveness of sunflower and wild host plants for oviposition was also investigated and showed that females preferred to lay eggs on wild host plants, compared with sunflower. These results may explain why N. natalensis will lay their eggs on sunflower after weeds in the vicinity are controlled, or senesce toward the end of the growing season.
Pest Management Science, Feb 9, 2023
BACKGROUNDTuta absoluta (Lepidoptera: Gelechiidae) is difficult to control by means of foliar ins... more BACKGROUNDTuta absoluta (Lepidoptera: Gelechiidae) is difficult to control by means of foliar insecticides, partly because of the endophytic feeding behavior of its larvae. The biopesticide spinosad is applied as a foliar spray for control of T. absoluta and has systemic properties when applied as a soil drench to the growing medium of tomato plants. The aims of this study were to determine the: (i) instar‐dependent tolerance of larvae to spinosad; (ii) efficacy of spinosad drench application for the control of larvae; (iii) residual period of systemic activity of spinosad in leaves and fruit after drenching; and (iv) effect of spinosad drenching on tomato plant growth parameters.RESULTSThe estimated LC50 value (Lethal Concentration at which 50% of the larvae died) differed between instars. The LC50 for second‐instar larvae (0.41 ppm) to spinosad was significantly lower than that for third‐ (0.64 ppm) and fourth‐instar (0.63 ppm) larvae. The LC80 value (Concentration at which 80% of the larvae died) for fourth‐instar larvae (2.48 ppm) was 2.6‐ and 1.7‐fold higher than that for the second‐ and third‐instar larvae, respectively. The spinosad concentration recorded in leaves at 25 days after treatment (DAT; 0.26 μg g−1) was significantly lower than that in leaves sampled at 3, 10 and 15 DAT. High larval mortalities were, however, recorded for the duration of the experiment, which lasted 25 days (equivalent to one T. absoluta generation).CONCLUSIONSystemic spinosad effectively controlled T. absoluta larvae over a prolonged period. However, drenching this insecticide violates the recommendation of the Insecticide Resistance Action Committee to avoid treating consecutive insect generations with the same mode of action and can therefore result in the evolution of insecticide resistance. © 2023 The Authors. Pest Management Science published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry.
Entomologia Generalis, Oct 25, 2022
Environmental Entomology, Feb 17, 2017
Previous studies into third trophic level exposure of Chrysoperla spp. (Neuroptera: Chrysopidae) ... more Previous studies into third trophic level exposure of Chrysoperla spp. (Neuroptera: Chrysopidae) to Cry1Ab proteins produced by Bt crops yielded contradicting results. These contradictions were largely ascribed to differences in prey quality and exposure methods. In this study, we used healthy prey to expose lacewing larvae to Cry1Ab protein produced by Bt maize, and also determined the concentration of this protein at different trophic levels. Experiments were conducted in which Chrysoperla pudica (Navás) larvae were fed different diets which included aphids and healthy Bt-resistant Busseola fusca (Fuller) (Lepidoptera: Noctuidae) larvae feeding on Bt maize tissue. Lacewing larval and pupal development times as well as overall mortality were determined. The concentration of Cry1Ab protein in B. fusca larvae were fourfold reduced compared with that in leaf tissue and was below detection level in lacewing larvae. Survival to the pupal stage was higher than 96% in all treatments. Larval and pupal development periods did not differ significantly between treatments in which prey fed on Bt or non-Bt maize. This study showed feeding on healthy prey that consumed Cry1Ab protein has no adverse effect on the biology of C. pudica.
The South African Journal of Plant and Soil, 2005
No insecticide is currently registered for Nysius natalensis Evans (Hemiptera: Orsillidae), contr... more No insecticide is currently registered for Nysius natalensis Evans (Hemiptera: Orsillidae), control on sunflower [Helianthus annuus l. (Asteraceae)]. Field as well as laboratory trials were conducted to evaluate efficacy of insecticides for N. natalensis control. During budding prior to ar:lthesis, insecticides were applied aerially. These were endosulfan, a mixture of dichlorvos + monocrotophos, mevinphos, a mixture of endosulfan + cypermethriri, methomyl and cypermethrin Compared to the untreated control, all insecticides provided effective control of N. natalensis. However, re-infestation by the pest occurred in ali treatments after five days. A laboratory evaluation of the efficacy of the contact action of eleven insecticides in controlling N. natalensis adults on sunflower heads during application or immediately thereafter was conducted. Insecticides were representative of different groups and modes of action. These were carbosulfan, methomyl, endosulfan, demeton-S-methyl, dichlorvos, chlorpyrifos, malathion, profenofos, cypermethrin, fenvalerate and tau-fluvalinate. The insecticides were applied to sunflower heads containing 50 N. natalensis adults in plastic containers. All insecticides controlled N. natalensis effectively. The efficacy of the eleven insecticides against N. natalensis adults that re-infest sprayed fields from three hours post-application onward, were also evaluated. The insecticides were applied as full cover sprays to. sunflower plants in the field. Disks were cut from the leaves three hours after treatment and placed in small plastic containers. Adults were transferred to the treated leaves and evaluated against those on leaves treated with water only. Fenvalerate and tau-fluvalinate were less effective in controlling N. natalensis than the other insecticides evaluated. Reduction in efficacy of seven of the insecticides was evaluated over a period of 14 days. Systemic insecticides remained more effective over longer periods than contact insecticides. However, the contact action of endosulfan remained as effective as the systemic insecticide, demeton-S-methyl. Endosulfan has a low toxicity to bees and will therefore control N. natalensis without a detrimental effect on pollination. To limit the number of applications, correct timing of insecticide application is important. The period that sunflower heads take to turn downward after completion of anthesis will determine the period for application of insecticides against N. natalensis during seed fill.
Uploads
Papers by Hannalene Du Plessis