No abstract

Chebet F., Deng A.L., Ogendo J.O, Kamau A.W., Bett P.K. (2013)

In an effort to find eco-friendly alternatives to synthetic pesticides in grain storage, residual contact toxicity and repellence of Cupressus lusitanica and Eucalyptus saligna leaf essential oils were evaluated against adult Tribolium castaneum, Acanthoscelides obtectus and Sitophilus zeamais. In bioassays, oil was applied at 0.00, 0.05, 0.10, 0.15 and 0.20% v/w to wheat and bean grains and stored for 30-120 days after which test insects were introduced into sub-samples of treated grains. Both oils at 0.20% v/w and 120 days grain storage duration caused a mortality of 5.0-65.0% in test insects whereas in the repellence bioassay, at same doses and grain storage duration produced percent repellence values of 34-52.4% of test insects. Considering other pesticidal properties of C. lusitanica and E. saligna oils, current results point oils as potential residual contact toxicants and repellents for possible integration into insect pest management practices.

No abstract

Botanical insecticides offer an environmentally benign insect pest management option for field crops with reduced impacts on natural enemies of pests and pollinators while botanically rich field margins can augment their abundance. Here, we evaluated the non-target effects on natural enemies and pest control efficacy on bean aphids in Lablab of three neem-and pyrethrum-based botanical insecticides (Pyerin75EC®, Nimbecidine® and Pyeneem 20EC®) and determine the influence of florally rich field margin vegetation on the recovery of beneficial insects after treatment. The botanical insecticides were applied at the early and late vegetative growth stages. Data were collected on aphids (abundance, damage severity and percent incidence) and natural enemy (abundance) both at pre-spraying and post-spraying alongside Lablab bean yield. The efficacy of botanical insecticides was similar to a synthetic pesticide control and reduced aphid abundance by 88% compared with the untreated control.However, the number of natural enemies was 34% higher in botanical insecticidetreated plots than in plots treated with synthetic insecticide indicating that plantbased treatments were less harmful to beneficial insects. The presence of field margin vegetation increased further the number of parasitic wasps and tachinid flies by 16% and 20%, respectively. This indicated that non-crop habitats can enhance recovery in beneficial insect populations and that botanical insecticides integrate effectively with conservation biological control strategies. Higher grain yields of 2.55-3.04 and 2.95-3.23 t/ha were recorded for both botanical insecticide and synthetic insecticide in the presence of florally enhanced field margins in consecutive cropping seasons. Overall, these data demonstrated that commercial botanical insecticides together with florally rich field margins offer an integrated, environmentally benign and sustainable alternative to synthetic insecticides for insect pest management and increased productivity of the orphan crop legume, Lablab.

Insect pests still cause substantial quantitative and qualitative grain loss ranging from 20 to 100% in small holder farming systems in tropical countries. Synthetic pesticides are recommended as stop gap measures for the management of stored product insect pests. However, their application has not been fully exploited in small scale farming due to environmental, health, and economic concerns. As a result, new researches have shifted focus to exploiting pesticidal plants as alternatives to synthetic pesticides. Therefore, the current study evaluated mixtures of plant powders and reduced amount of Actellic superTM (pirimiphos-methyl + permethrin) as alternative insecticide formulation against Callosobruchus chinensis and Sitophilus zeamais. Green grams and wheat grains were mixed with a mixture of plant powders in the ratios of 1:1, 1:3 and 1:9 to obtain four rates (0.0, 2.0, 6.0 and 10%w/w). Grains and plant powders were also mixed with reduced amount (10, 25, and 50 %) of recommended rate of Actellic SuperTM to obtain dosages as above. Twenty unsexed adults, 1-5 day old S. zeamais and C. chinensis were introduced into treated grains. The mixture of C. lusitanica: T. vogelii powders in the ratios of 1:1, 1:3 and 1:9 caused mortality in C. chinensis of 55, 95 and 85%, respectively. At the same ratio, E. saligna: L. camara mixture produced mortality in S. zeamais of 77, 82, and 85% respectively. In mixture of C. lusitanica and T. vogelii and reduced amount of Actellic SuperTM by 50% the mortality of C. chinensis was 85 and 80 % respectively. Similarly, E. saligna and L. camara and reduced amount of Actellic SuperTM by 50% caused a mortality of S. zeamais of 48 and 97% respectively. The application of plant powders and reduced amounts of synthetic insecticide has the potential to be applied in stored product pest control

Despite beans being a vital source of cheap protein, its yield is reduced mainly by diseases, field and storage pests. An effective and sustainable control option against storage insect pests could be improving the genetic resistance of the host plant in relation to the behaviour of the pest.  A laboratory investigation was conducted to determine effects of bean varieties on oviposition behaviour and susceptibility to infestation by Acanthoscelides obtectus. The experiments evaluated oviposition site preference, number of eggs laid, and number of progeny and emergence holes of A. obtectus per bean variety. The number of progeny and duration in days taken by 50 % of progeny to emerge was determined and used to calculate susceptibility index. Seed harness index, thickness of testae and surface area of bean varieties were determined and related with susceptibility indices.  Results indicated that the number of eggs laid, progeny, and emergence holes, duration taken by progeny to emerge, susceptibility indices, seed surface area and hardness were statistically different. Mwezi moja variety was the most preferred host for oviposition whereas Mwitemania was the least preferred. Beetles laid the highest (84.5) number of eggs in Mwezi moja and the least (41.9) in Mwitemania. Number of progeny of A. obtectus emerging were the highest in Mwezi moja (73.7) and the least (36) in Mwitemania. Beetles took the shortest (36.75 days) period to emerge from Mwezi moja and the longest (38.63days) period from Mwitemania. Mwezi moja was the most susceptible variety to attack by A. obtectus with a susceptibility index of 7.43 and Mwitemania was the least susceptible with an index of 6.51. Nyayo had the highest (0.019) seed hardness index and Mwezi moja and Canadian wonder had the least (0.012) hardness index. Mwezi moja had the largest (278mm) surface area whereas Mwitemania had the lowest (171mm) surface area.