The impact of conventional and organic farming on soil biodiversity conservation: a case study on termites in the long-term farming systems comparison trials in Kenya

A long-term experiment at two trial sites in Kenya has been on-going since 2007 to assess the effect of organic and conventional farming systems on productivity, profitability and sustainability. During these trials the presence of significant numbers of termites (Isoptera) was observed. Termites are major soil macrofauna and within literature they are either depict as ‘pests’ or as important indicator for environmental sustainability. The extent by which termites may be managed to avoid crop damage, but improve sustainability of farming systems is worthwhile to understand. Therefore, a study on termites was added to the long-term experiments in Kenya. The objectives of the study were to quantify the effect of organic (Org) and conventional (Conv) farming systems at two input levels (low and high) on the abundance, incidence, diversity and foraging activities of termites. The results showed higher termite abundance, incidence, activity and diversity in Org-High compared to Conv-High, Conv-Low and Org-Low. However, the termite presence in each system was also dependent on soil depth, trial site and cropping season. During the experiment, nine different termite genera were identified, that belong to three subfamilies: (i) Macrotermitinae (genera: Allodontotermes, Ancistrotermes, Macrotermes, Microtermes, Odontotermes and Pseudocanthotermes), (ii) Termitinae (Amitermes and Cubitermes) and (iii) Nasutitiermitinae (Trinervitermes). We hypothesize that the presence of termites within the different farming systems might be influenced by the types of input applied, the soil moisture content and the occurrence of natural enemies. Our findings further demonstrate that the organic high input system attracts termites, which are an important, and often beneficial, component of soil fauna. This further increases the potential of such systems in enhancing sustainable agricultural production in Kenya

Insecticide contamination in organic agriculture: Evidence from a long-term farming systems comparison trial

Synthetic pesticides applied in conventional agriculture to control pests tend to compromise ecosystem services, and their residues may contaminate organic agriculture. To understand the significance of this contamination, also in small-scale farming systems in sub-Saharan Africa, quantitative data is required. Therefore, we compared synthetic insecticide and botanical/biopesticide residues in conventional and organic agricultural production systems after nine years of continuous cultivation of a maize-based crop rotation system at two sites in Kenya. Our results show high detectable concentrations of synthetic insecticide residues (imidacloprid, acetamiprid, chlorpyrifos, and chlorantraniliprole) in conventional plant produce and soil. Furthermore, the organophosphate chlorpyrifos was detected at concentrations above European Union Maximum Residue Limits (MRL) for plant produce, indicating potential risks for human health. Additionally, we detected imidacloprid, acetamiprid, chlorpyrifos, and chlorantraniliprole concentrations in the soil, indicating potential environmental harm. No residues of biopesticide/botanicals were detected in any of the production systems. However, we detected imidacloprid and chlorantraniliprole in organic plots. The findings indicate that the MRLs can be crossed even if synthetic insecticides are applied according to or below the recommended rates on the conventional plots. Thus, synthetic insecticides potentially risk human health and the environment, while botanicals and bio-pesticides represent a safe alternative

Visual cues from different trap colours affect catches of Sahlbergella singularis (Hemiptera: Miridae) in sex pheromone traps in Cameroon cocoa plantations

Cocoa mirids, Sahlbergella singularis and Distantiella theobroma, are the most economically important insect pests of cocoa in West and Central Africa, where they can cause up to 40% losses in cocoa yields. Sahlbergella singularis is the most common species in Cameroon and was therefore targeted in this study. During a two-year trial in 15 cocoa plantations in Ayos and Konye, in the Centre and Southwest regions of Cameroon respectively, the most effective colour – white, purple or green – of sex pheromone traps was examined for integration into mirid management programmes. Similar temporal patterns in S. sahlbergella male trap catches were observed with all three colours, but the green trap caught more S. singularis (Ayos: 0.968 ± 0.091 [SEM]; Konye: 0.640 ± 0.076/trap/month) compared with purple traps (Ayos: 0.674 ± 0.068; Konye: 0.441 ± 0.058), and white traps (Ayos: 0.467 ± 0.049, Konye: 0.253 ± 0.041). Trap reflectance showed wavelength peaks typical for purple in both short (approximately 380 - 480 nm) and long wavelengths (> 650 nm), and ~530 nm for green. Reflectance peaks exceeded 100% of the incident light in the 400-450 nm range from the white, suggesting the presence of optical brighteners. Trap catches support the hypothesis that S. singularis ocelli are more responsive to light of shorter wavelengths. Despite the low attractiveness of the sex pheromone to S. singularis, a optimisation of the colour of the trap can improve S. sahlbergella monitoring, mass trapping, and other control measures which could ultimately lead to reductions of insecticide use and to conservation of beneficial arthropods, particularly cocoa flower pollinators that are critical for improving cacao tree productivity

Behavioural responses of bean flower thrips (Megalurothrips sjostedti) to vegetative and floral volatiles from different cowpea cultivars

Bean flower thrips (Megalurothrips sjostedti) is a key pest of cowpea (Vigna unguicalata) in Africa. To better understand the interaction of M. sjostedti to cowpea cultivars to improve management efforts, we investigated the repellent properties of volatiles of four cowpea cultivars, namely Ex-Luanda, Machakos, Ken Kunde 1 and Katumani 80 at different phenological stages. Bioassays were conducted to study host preference and gas chromatography–mass spectrometry for chemical analysis of volatiles. Our results showed no significant preference of females M. sjostedti for any cowpea cultivars tested in preference assays. However, in olfactometer, the volatiles emitted during the vegetative stage of only Ex-Luanda, Machakos and Katumani 80 cultivars were repellent to females, while only Ken Kunde 1 was repellent to males. Volatiles from flowers of Ken Kunde 1 were attractive to females, whereas volatiles from the flowers of Katumani 80 were repellent, respectively. Ex-Luanda and Machakos elicited neutral response. Flowers of Machakos 66 and Ex-Luanda cultivars were repellent to males, while Katumani 80 and Ken Kunde 1 were neutral. The volatile analysis showed that (E)-β-ocimene and 1-octen-3-ol were unique to the volatile profile of Katumani 80 flowers. Previous study showed that (E)-2-hexenal and hexanal were only abundant in the vegetative stage of Katumani 80. (E)-2-hexenal was repellent to the females at a concentration of 0.01% but not at 1%. Hexanal, (E)-β-ocimene and 1-octen-3-ol elicited a neutral response from females at 0.01% and 1%. Our study indicates that (E)-2-hexenal could be useful in the development of semiochemical-based repellent tools for M. sjostedti management

Repellent activity of Cymbopogon citratus and Tagetes minuta and their specific volatiles against Megalurothrips sjostedti

Cowpea is an important source of protein for people in Africa. However, the crop suffers major damage and yield losses due to bean flower thrips, Megalurothrips sjostedti Trybom (Thysanoptera: Thripidae). Although companion plants are known to reduce the damage caused by insect pests, the role of their volatiles in repelling pests from target plants has been the subject of few investigations. Here, we used the Y‐tube olfactometer experiments and chemical analyses to investigate the effect of volatiles from cowpea flowers and two companion plants; lemongrass, Cymbopogon citratus and Mexican marigold, Tagetes minuta on the olfactory responses of M. sjostedti. The results revealed that M. sjostedti males and females were repelled by the volatiles from freshly cut leaves of C. citratus. The combination of freshly cut leaves of C. citratus and cowpea flower was repellent to females but not to males. The female thrips, but not males, were repelled by the volatiles from the vegetative stage of T. minuta. Fifty‐four compounds were identified in the volatiles from two herbal plants. Among the major compounds, citral and a 4‐component blend comprised of dihydrotagetone, (Z)‐3‐hexenyl acetate, limonene and (Z)‐β‐ocimene repelled females but dihydrotagetone alone attracted females. While myrcene combined with cowpea flower volatiles enhanced the attraction of females M. sjostedti, when tested alone was not attractive. These results highlight the potential of volatiles from C. citratus and T. minuta to repel M. sjostedti females. The use of these plants as companion plants in a cowpea cropping system could reduce M. sjostedti infestation