The fall armyworm (FAW)Spodoptera frugiperdais thought to have undergone a rapid ‘west-to-east’ spread since 2016 when it was first identified in western Africa. Between 2018 and 2020, it was recorded from South Asia (SA), Southeast Asia (SEA), East Asia (EA), and Pacific/Australia (PA). Population genomic analyses enabled the understanding of pathways, population sources, and gene flow in this notorious agricultural pest species. Using neutral single nucleotide polymorphic (SNP) DNA markers, we detected genome introgression that suggested most populations in this study were overwhelmingly C- and R-strain hybrids (n = 252/262). SNP and mitochondrial DNA markers identified multiple introductions that were most parsimoniously explained by anthropogenic-assisted spread, i.e., associated with international trade of live/fresh plants and plant products, and involved ‘bridgehead populations’ in countries to enable successful pest establishment in neighbouring countries. Distinct population genomic signatures between Myanmar and China do not support the ‘African origin spread’ nor the ‘Myanmar source population to China’ hypotheses. Significant genetic differentiation between populations from different Australian states supported multiple pathways involving distinct SEA populations. Our study identified Asia as a biosecurity hotspot and a FAW genetic melting pot, and demonstrated the use of genome analysis to disentangle preventable human-assisted pest introductions from unpreventable natural pest spread.

Cassava is a staple food for people across sub-Saharan Africa. Over the last 20 years, there has been an increased frequency of outbreaks and crop damage in this region caused by the cassava-adapted Bemisia tabaci putative species. Little is known about when and why B. tabaci adults move and colonize new cassava crops, especially in farming systems that contain a mixture of cultivar types and plant ages. Here, we assessed experimentally whether the age and variety of cassava affected the density of B. tabaci. We also tested whether the age and variety of the source cassava field affected the variety preference of B. tabaci when they colonized new cassava plants. We placed uninfested potted “sentinel” plants of three cassava varieties (Nam 130, Nase 14, and Njule Red) in source fields containing one of two varieties (Nam 130 or Nase 14) and one of three age classes (young, medium, or old). After two weeks, the numbers of nymphs on the sentinel plants were used as a measure of colonization. Molecular identification revealed that the B. tabaci species was sub-Saharan Africa 1 (SSA1). We found a positive correlation between the density of nymphs on sentinel plants and the density of adults in the source field. The density of nymphs on the sentinels was not significantly related to the age of the source field. Bemisia tabaci adults did not preferentially colonize the sentinel plant of the same variety as the source field. There was a significant interactive effect, however, between the source and sentinel variety that may indicate variability in colonization. We conclude that managing cassava source fields to reduce B. tabaci abundance will be more effective than manipulating nearby varieties. We also suggest that planting a “whitefly sink” variety is unlikely to reduce B. tabaci SSA1 populations unless fields are managed to reduce B. tabaci densities using other integrative approaches.

The life table statistics of six native Kenyan species/strains ofTrichogrammaandTrichogrammatoideawere established using a factitious hostCorcyra cephalonica, Stainton (Lepidoptera: Pyralidae), at eight different temperatures (10, 15, 20, 25, 28, 30, 32 and 35°C) and two humidity levels (40–50 and 70–80%). The objective was to select insects with superior attributes for augmentative release against lepidopteran pests in horticultural crops. Both temperature and humidity affected developmental time and life table parameters of the parasitoids but temperature played a more critical role. Developmental time was inversely related to temperature. The intrinsic and finite rates of increase increased with temperature up to 30°C. Both net reproduction rate and intrinsic rate of increase were higher at the lower humidity. Temperature inversely affected generation time of parasitoid strains regardless of the relative humidity. Two strains ofTrichogrammasp. nr.mwanzaicollected from both low and medium altitudes andTrichogrammatoideasp. nr.luteafrom the mid-altitudes, were better adapted to both low and high temperatures than the other strains, as indicated by the high intrinsic and net reproductive rates, at both humidity levels. These three strains appear to be promising candidates for augmentation biocontrol against the African bollwormHelicoverpa armigerain Kenya.

Six native Kenyan species/strains of Trichogramma and Trichogrammatoidea, recovered from Helicoverpa armigera were evaluated at six different temperatures (10, 15, 20, 25, 30 and 35°C) and two relative humidity levels (40–50 and 70–80%) with the aim of selecting strains adapted to warmer temperature regimes. The species/strains were collected from low (1200 m) locations and were evaluated for parasitism, adult longevity, progeny production and progeny sex ratio at the different environmental regimes. Eggs of the factitious host, Corcyra cephalonica Stainton (Lepidoptera: Pyralidae) were used in the investigations. Temperature and humidity interactions affected parasitism and progeny production. The highest parasitism at the two humidity levels was at 25 and 30°C for all the strains evaluated. Adult longevity was also significantly affected by the interaction of temperature and relative humidity and was longer at the lower than higher relative humidity. Survival followed a type I survivorship curve at lower temperatures and a type III survivorship curve at the higher temperatures. Trichogramma sp. nr. mwanzai from low altitude, Trichogramma sp. nr. mwanzai from medium altitude and Trichogrammatoidea sp. nr. lutea also from medium altitude lived longer than other strains at all the temperatures and relative humidity levels evaluated, including the warmest regimes of 30 and 35°C. These strains appear promising as candidates for augmentative biocontrol of H. armigera in Kenya.

Background: The Fall armyworm (FAW) Spodoptera frugiperda (Lepidoptera: Noctuidae) is now established across the African continent and is a highly polyphagous and destructive pest of many crops. In Uganda, FAW has become the major maize pest, causing heavy damage especially on shoots and growing points. The objectives of this study were to: (i) document local farming practices that have been useful to manage FAW, (ii) establish farmers’ perspective on the time of FAW’s arrival to their localities, (iii) investigate the economic impact (yield) of FAW to maize farmers, (iv) establish the farmers’ perception on the current status of the FAW, and (v) document alternative practices used to manage the FAW and the perceived efficacies. Methods: A questionnaire survey was undertaken in November 2020 in Kamuli and Namutumba districts of Uganda and 99 farmers were interviewed to understand their profiles and perceptions about the FAW. A descriptive analysis of this data was undertaken to establish the socio-economic profiles and perceptions of the farmers. Results: Farmers’ education levels in the two districts ranged from basic (completed primary education) to advanced (completed University degree), with most farmers having 10–30 years experience in growing maize (F = 20.8; df = 3,7; P = 0.0067), and with mainly small- and mid-sized production scales (F = 436.2; df = 2,5; P = 0.0002). Famers in Kamuli (98%) and Namutumba (96%) reported 25–50% yield losses due to FAW infestation that negatively impacted their income. We found a significantly higher percentage of farmers (84% and 92% in Kamuli and Namutumba districts, respectively), could correctly identify the FAW by its appearance (P < 0.0001). While FAW was officially reported in Uganda in 2016, farmers confirmed noticing damage symptoms similar to those caused by FAW as early as 2013 and 2014 in Namutumba and Kamuli districts, respectively. 98% of the farmers in Kamuli and 96% of those in Namutumba strongly agreed that FAW infestation reduced their income, while 74% in Kamuli and 86% in Namutumba also strongly considered the FAW as a threat to maize production (P < 0.0001). The majority of farmers (64% in Kamuli, 82% in Namutumba) still considered the FAW to be a very serious challenge to maize production in their localities, six years since officially being reported in Uganda. To manage the FAW, 84% and 90% of Kamuli and Namutumba respondents respectively, predominantly use chemical control methods. Other methods used also included cultural control practices (i.e., by regular weeding and handpicking), while the use of biological extracts (pepper, tobacco, Aloe-vera, Lantana, sisal) was evident though not common. Pheromones and biological control methods to manage FAW were not reported, although a farmer in Kamuli district reportedly observed weaver birds (Ploceus spp.) predating on the FAW in maize. A small number of farmers (ca. 4%) in both districts reportedly took no intentional action against FAW. Conclusions: The farmers believe they can manage FAW if they have the appropriate and efficacious chemical insecticides as they are able to correctly apply them and follow recommended procedures. The farmers advocated for an area-wide approach as one of the best alternatives to manage this invasive pest.

Cassava (Manihot esculenta Crantz), an important commercial and food security crop in East and Central Africa, continues to be adversely affected by the whitefly Bemisia tabaci. In Uganda, changes in smallholder farming landscapes due to crop rotations can impact pest populations but how these changes affect pest outbreak risk is unknown. We investigated how seasonal changes in land-use have affected B. tabaci population dynamics and its parasitoids. We used a large-scale field experiment to standardize the focal field in terms of cassava age and cultivar, then measured how Bemisia populations responded to surrounding land-use change. Bemisia tabaci Sub-Saharan Africa 1 (SSA1) was identified using molecular diagnostics as the most prevalent species and the same species was also found on surrounding soybean, groundnut, and sesame crops. We found that an increase in the area of cassava in the 3–7-month age range in the landscape resulted in an increase in the abundance of the B. tabaci SSA1 on cassava. There was a negative relationship between the extent of non-crop vegetation in the landscape and parasitism of nymphs suggesting that these parasitoids do not rely on resources in the non-crop patches. The highest abundance of B. tabaci SSA1 nymphs in cassava fields occurred at times when landscapes had large areas of weeds, low to moderate areas of maize, and low areas of banana. Our results can guide the development of land-use strategies that smallholder farmers can employ to manage these pests.