Sitophilus Spp Research Articles

Coordination of host and endosymbiont gene expression governs endosymbiont growth and elimination in the cereal weevil Sitophilus spp.

BackgroundInsects living in nutritionally poor environments often establish long-term relationships with intracellular bacteria that supplement their diets and improve their adaptive and invasive powers. Even though these symbiotic associations have been extensively studied on physiological, ecological, and evolutionary levels, few studies have focused on the molecular dialogue between host and endosymbionts to identify genes and pathways involved in endosymbiosis control and dynamics throughout host development.ResultsWe simultaneously analyzed host and endosymbiont gene expression during the life cycle of the cereal weevil Sitophilus oryzae, from larval stages to adults, with a particular emphasis on emerging adults where the endosymbiont Sodalis pierantonius experiences a contrasted growth-climax-elimination dynamics. We unraveled a constant arms race in which different biological functions are intertwined and coregulated across both partners. These include immunity, metabolism, metal control, apoptosis, and bacterial stress response.ConclusionsThe study of these tightly regulated functions, which are at the center of symbiotic regulations, provides evidence on how hosts and bacteria finely tune their gene expression and respond to different physiological challenges constrained by insect development in a nutritionally limited ecological niche.Graphical C-ALjyaRxUENP7MJ-64adUVideo

Evaluation of the Efficacy of Beetle Lure (BFL 225) and Bullet Synthetic Multi-Attractant as Insect Baits in Untreated Grain Storehouses

An experiment was carried out to evaluate the efficacy of synthetic general beetle lure and bullet synthetic multi attractant in trapping insects in untreated grain stores. Four grain stores (two each) in two major markets within Calabar metropolis, were sampled at random and selected for this research. Three groups of four traps each with sticky bases were treated as follows: Trap group “A” was treated with BFL225 pheromone multi-attractant, Trap group “B” was treated with bullet lure multi-attractant pheromone and Trap group “C” was untreated (control). This experiment was replicated on monthly basis for a period of eight months to also ascertain the influence of weather conditions on trapped insect population. Insects caught were identified base on the different trap efficacy and recorded following the method in Ukeh and Mordue, (2009). All traps were re-treated monthly for efficient trapping. Data obtained from the experiment were laid out as factorial in CRD and subjected to analysis of variance using GenStat statistical software (Version 6). Significant means were compared using LSD and DNMRT at 5 percent level of probability. Insects trapped and identified include Sitophilus spp , Corcyra ciphilonica, Tribolium castaneum and Callosobrochus maculatus. The treated trap groups (A and B) significantly (p<0.05) caught more insects than the untreated trap group (control). However, between the treated trap groups, the BFL 225 significantly (p<0.05) caught more insects than the bullet lure treated trap. The number of insets caught also varied significantly (p<0.05) with different months. The wet month of August significantly had the highest number of insects followed by June. The dry months of January and February also had high number of insects relative to the other months. The least number of insects caught were obtained in the months of April and May. The interaction between the trap treatment type and month was significant (p<0.05). Generally, higher number of insects were caught in both treated and untreated trap groups in the wet month (June – August) compared to other months. BFL 225 treated trap groups significantly caught the highest number of insects in August, followed by the bullet treated trap group and the untreated in the same month. The bullet lure treated traps caught the least number on insects in April and May and was not significantly (p<0.05) different from the number caught by untreated trap (control) in the month of April. The trap treated with BFL225 caught the highest number of insect. Hence, this research supports the use of BFL 225 as an efficient tool in integrated pest management approach for stored grains. Keywords: Beetle lure, Bullet synthetic, Insects, Pheromone, Treated traps. DOI: 10.7176/JBAH/12-20-03 Publication date: October 31 st 2022

Potentials of Three Plants Leave oils mixture in Protecting Maize Grains against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Over the last decade, Sitophilus zeamais are being control using synthetic insecticides. The over- use of these chemicals has lead to the development of insecticides resistance, environmental pollution, and killing of non-target organisms. The efficacy of Hyptis suaveolens, Ocimum gratissimum, and Psidium guajava leaf oils combination against adult S. zeamais was investigated on maize grain during the study. The leaves of the plants were grounded into powders and oils were extracted using Soxhlet apparatus separately. Maize variety 99% EDVT used was obtained from the International Institute for Tropical Agriculture (IITA) Kano. The insects were cultured in a containers and identified using a standard taxonomic key for Sitophilus spp. Different oils combination of two plants leaves oils were made in the ratio of 50%:50% of the test dose 0.1, 0.2, 0.3, and 0.4ml/20g.Ten newly emerged S. zeamais were introduced separately for examination of adult mortality test and lethal concentration determination. Results showed that mortality increases with exposure period. The leaves oils combination show a significant difference in adult mortality of S. zeamais (P<0.05). Isobutylcyclohexane, Oleic Acid and 11-octadecenoic acid were the most occurring compound present in the individual plant extract. H. suaveolens and O. gratissimum combination protecting maize grains against S. zeamais infestation and therefore, the active ingredient of these plant combinations should be evaluated.

O óleo essencial de Pimenta racemosa é eficiente inseticida para controle de Sitophilus spp. (Coleoptera: Curculionidae) em grãos armazenados

Os produtos formulados a partir de plantas possuem uma gama de compostos ativos, dos quais muitos apresentam efeitos inseticidas já comprovados, podendo ser atraentes ou repelentes aos insetos, servindo assim como alternativa no controle das populações de insetos-praga. Assim sendo, o presente estudo objetivou investigar a potencial atividade inseticida de óleos essenciais e métodos de aplicação sobre Sitophilus spp. em grãos de feijão (Phaseolus vulgaris) sob atmosfera controlada. Os óleos essenciais utilizados foram: Cymbopogon citratus (citronela), Cymbopogon nardus (capim-limão) e Pimenta racemosa (pimenta-gim), os quais foram aplicados em dois métodos em grãos de feijão, direta e indiretamente. Constatou-se um efeito inseticida sobre Sitophilus spp. decorrente da aplicação de óleos essenciais em grãos de feijão. Obteve-se maior efeito inseticida no tratamento com óleo essencial de pimenta-gim sendo que a segunda maior mortalidade média foi apresentada pelo óleo de capim limão. Estes resultados demostram que estes dois óleos são eficientes para manejo de Sitophilus spp. nas primeiras 72 horas posteriores a aplicação.

Diversity and convergence of mechanisms involved in pyrethroid resistance in the stored grain weevils, Sitophilus spp.

Target-site mutations and changes in insect metabolism or behavior are common mechanisms in insecticide-resistant insects. The co-occurrence of such mechanisms in a pest strain is a prominent threat to their management, particularly when alternative compounds are scarce. Pyrethroid resistance among stored grain weevils (i.e., Sitophilus spp.) is an example of a long-standing concern, for which reports of resistance generally focus on a single mechanism in a single species. Here, we investigated pyrethroid resistance in maize and rice weevils (i.e., Sitophilus zeamais and S. oryzae), exploring potential knockdown resistance (kdr) mutations in their sodium channels (primary site for pyrethroid actions) and potential changes in their detoxification and walking processes. Resistance in pyrethroid-resistant rice weevils was associated with the combination of a kdr mutation (L1014F) and increases in walking and detoxification activities, while another kdr mutation (T929I) combined with increases in walking activity were the primary pyrethroid resistance mechanisms in maize weevils. Our results suggest that the selection of pyrethroid-resistant individuals in these weevil species may result from multiple and differential mechanisms because the L1014F mutation was only detected in Latin American rice weevils (e.g., Brazil, Argentina and Uruguay), not in Australian and Turkish rice weevils or Brazilian maize weevils.

Toxicity Test on Wedusan (Ageratum spp.) Extract Against Sitophilus spp. (Coleoptera: Curculionidae)

Tropical condition in Southeast Asia has contributed around 30% of post harvest damage as it provide optimum condition for the growth of Sitophilus spp. pest. Therefore, this study was aimed to investigate the effect of wedusan extract on controlling Sitophilus spp. Growth. Wedusan extract was given in different level of concentrations. The research used the Randomized Complete Design. Wedusan ( Ageratum spp.) extract affected the imago mortality of Sitophilus spp. There were two kinds of Wedusan extract used in this study, dried extract (DE) and fresh extract (FE). Sitophilus imago were put into bottles filled with organic rice and were treated with Wedusan extract. The mortality level was obsered at 24 Hours After Application (HAA), 48 HAA, and 72 HAA. The highest toxicity was found by the treatment of dried extract of wedusan 5 tablets, by LC50 55% on 24 HAA and 82.25% on 72 HAA. Extract of dry matter has higher toxicity effect than fresh extract. The application of wedusan extract is eviromental friendly and specific-range against pest. It is promising for future development as natural product in agriculture area.

An IMD-like pathway mediates both endosymbiont control and host immunity in the cereal weevil Sitophilus spp.

Many insects developing on nutritionally unbalanced diets have evolved symbiotic associations with vertically transmitted intracellular bacteria (endosymbionts) that provide them with metabolic components, thereby improving the host’s abilities to thrive on such poor ecological niches. While host-endosymbiont coevolutionary constraints are known to entail massive genomic changes in the microbial partner, host’s genomic evolution remains elusive, particularly with regard to the immune system. In the cereal weevil Sitophilus spp., which houses Sodalis pierantonius, endosymbionts are secluded in specialized host cells, the bacteriocytes that group together as an organ, the bacteriome. We previously reported that at standard conditions, the bacteriome highly expresses the coleoptericin A (colA) antimicrobial peptide (AMP), which was shown to prevent endosymbiont escape from the bacteriocytes. However, following the insect systemic infection by pathogens, the bacteriome upregulates a cocktail of AMP encoding genes, including colA. The regulations that allow these contrasted immune responses remain unknown. In this short report, we provide evidence that an IMD-like pathway is conserved in two sibling species of cereal weevils, Sitophilus oryzae and Sitophilus zeamais. RNA interference (RNAi) experiments showed that imd and relish genes are essential for (i) colA expression in the bacteriome under standard conditions, (ii) AMP up-regulation in the bacteriome following a systemic immune challenge, and (iii) AMP systemic induction following an immune challenge. Histological analyses also showed that relish inhibition by RNAi resulted in endosymbiont escape from the bacteriome, strengthening the involvement of an IMD-like pathway in endosymbiont control. We conclude that Sitophilus’ IMD-like pathway mediates both the bacteriome immune program involved in endosymbiont seclusion within the bacteriocytes and the systemic and local immune responses to exogenous challenges. This work provides a striking example of how a conserved immune pathway, initially described as essential in pathogen clearance, also functions in the control of mutualistic associations.

EFFECT OF PLANTING TIME AND STORAGE METHODS ON GRAIN WEEVILS, SITOPHILUS SPP (COLEOPTERA: CURCULIONIDAE) INFESTING WHEAT GRAINS

This research was conducted at special farms in Shebin Elkom locality to study the effect of planting wheat at five times (Oct. 30, Nov. 10, Nov. 16, Nov. 20, Nov. 26, 2012 ) and harvested at four times ( Apr. 4, Apr. 19, Apr. 22, Apr. 29, 2013) on the infestation of the grain weevils, Sitophilus spp, (Coleoptera: Curculionidae, along one year of storing at five tools (Metal silos, Mud silos, Polyethylene bags, Jute bags, Plastic fiber bags). Wheat grain samples (100 g) of each store model of stored grains were examined by eye and with the aid of handle lens (6 x) to calculate the average number of weevil insects per 100 g. Treatments were replicated three times. Statistical analysis of the obtained results indicated that there were significant differences in the annual weevil numbers among the planting times, the best planting time is 20 November because it has the lowest infestation numbers of weevil insects recording 4103 weevil / 100 g wheat grains, while the highest weevil numbers was recorded with the planting time 10 November giving 15796 weevil / 100 g wheat grains. Regarding to the storing tools, results indicated that there were significant differences in the annual weevil numbers between plastic fiber bags and all other tools recording the lowest numbers of grain weevil insects 5495 individual / 100 g. The highest annual numbers of grain weevils recorded in mud silos and polyethylene bags (10082- 10584 weevil / 100 g) respectively. From the obtained results it could be concluded that the suitable planting time to cultivate wheat is 20 November which resulted the lowest numbers of weevil insects, as well as the suitable tool for wheat grain storing is plastic fiber bags in comparison with other tools.

Relationship between insecticidal efficacy and oil absorption capacity of inert dusts against sitophilus spp.

Sixteen inert dusts were tested for their effects on bulk density, oil absorption capacity and insecticidal activity against Sitophilus oryzae and Sitophilus granarius: Sipernat 50S, Protector (Italy), Celite 209, SilicoSec (Germany), Dryacide (USA), KeepDry (Brazil), Mn 23, Protect-It (USA), MA-4 (Croatia), Mn 51, Clarcel (France), Perma Guard, DiaFil 610, Zeolite Osijek (large particles), Zeolite Osijek (small particles) and Huber 80 (USA). These dusts had differences in oil absorption capacity, reduction of bulk density and toxicity to insects. Sipernat 50S, the silica aerogel had the greatest capacity to absorb oil (3.23 mL/g dust), greatly reduced bulk density (to 71.9 kg/hL from 76.6 kg/hL in untreated wheat) and caused 90 to 100% mortality with S. granarius and S. oryzae. Zeolite and kaolin clay had the least effect on oil absorption, bulk density and mortality. The rest of the diatomaceous earth (DE) tested had intermediate values. Oil absorption capacity was positively correlated with mortality. The correlation for S. oryzae was lower (r2 = 0.44) than with S. granarius (r2 = 0.73). Mortality was negatively correlated with bulk density. Bulk density was negatively correlated with oil absorption.

Evaluating Grain Protectant Efficacy of Some Botanicals against Maize Weevil, Sitophilus zeamais M

The production of sorghum is threatened by a wide range of pre-and post harvest pests like stalk borer, sorghum chafer, and Sitophilus spp. Three botanical plants (Tagitus minuta, Datura stramonium and Carissa schimperi) with five concentrations were tested for efficacy to control maize weevil (Sitophilus zeamais Mostch) on stored sorghum seeds under laboratory conditions. The objective was to study the efficacy of some locally available botanicals to control Sitophilus zeamais Mostch and to determine the length of period the grain could be protected by the different treatments. For comparison, two more treatments-standard check Malathion 5% dust plus control (untreated check) were included; and the experiment was replicated three times. The experiment was conducted under room temperature at 25-28C and relative humidity at 70±5% in Kombolcha Plant Health Clinic Laboratory. Powders of each plant component were then mixed thoroughly with 500 gram grains in plastic jars roofed with muslin cloth and tightened with rubber band. Thirty adult weevils were released in each plastic jars. Number of dead weevils was recorded every 21, 42 and 84 days after the treatments were applied. The data was transformed to arcsine scale prior to analysis. Corrected observations were subjected to statistical analysis, factorial ANOVA. All botanicals significantly affected weevil mortality compared to untreated check, but not as effective as synthetic insecticides (Malathion 5% dust). Carissa schimperi (merez) 5% was significantly more effective than the rest botanical rates and the control (P <0.05). In general the result shows that treatment Carissa schimperi (merez) 5% and Tagitus minuta (gimi) 5% can solve poor resources farmers’ problems by integrating them with other cultural measures. However further research are needed to fix the rate graph and the long term effect in large stores of farmers conditions.

Comparing genetic diversity of Sitophilus zeamais (Motchulsky) popula-tions sampled in several agro-ecological areas between Central African Republic and Senegal

Maize is attacked by many post-harvest pests including Sitophilus spp and Prostephanus spp, which causes remarkable loss during storage. Approxi-mately 30 to 40 % loss in the absence of treatment has been reported world-wide. This study compare genetically Central African and Senegalese popula-tions of Sitophilus zeamais from various agroecological zones using 3 mark-ers namely cytochrome b, cytochrome oxidase and nuclear 28S gene. S. zeamais samples were analyzed on both of two other sites 34 for the 28S gene; 68 for cytochrome b and 36 for the cytochrome oxydase. Results ana-lyzed by AMOVA have shown high genetic variation outside population of each country (6.17 % with Cyt b; 21.45 % with 49.83 % and COI in the case of 28S) and low within subpopulations (-10.06 % for Cyt b, 9.36 % for the COI and -15.23 % for 28S). Majority haplotype is shared between the two popula-tions for 28S and cytochrome b genes and there is a very high haplotype di-versity in populations of Senegal considering the Cytochrome b gene (0.781 + / - 0.00364) while with COI and 28S, high values of diversity are observed in Central African sequences, respectively 1.000 + / - 0.00274 and 0.867 + / - 0.011. Genetic differentiation obtained according to the geographical origin is significant between the two populations; however, it is not at the level of subpopulations. Developed by the three approaches (parsimony, likelihood and Bayesian) phylogenetic trees are resolved and show a speciation of the two populations according to the geographical origin.

Insect population distribution and density estimates in a large rice mill in Portugal – A pilot study

The objectives of this study were to characterize the spatial distribution of the most abundant insect species identified in the rice plant, optimize the sampling program, develop and validate a fixed-precision enumerative sequential sampling plan for the key pests Sitophilus spp. in the rice industry in Portugal. Experiments were carried out from September 2005 to July 2007, using 25 pitfall traps baited with food grade oil and pheromone specific for Sitophilus spp. The traps were observed weekly and the insects were identified and counted. Several species were found but Sitophilus zeamais and Sitophilus oryzae were the most abundant (90% of the total) followed by Tribolium castaneum. Taylor's power law parameters, from the regression of log variance versus log mean, suggest an aggregated distribution for Sitophilus spp. and T. castaneum. A fixed-precision sequential sampling plan was developed for Sitophilus spp., using Green's fixed precisions sampling plan and the Resampling Validation of Sampling Plan, with an action threshold of 0.5 Sitophilus spp. The sampling plan was designed to provide precision levels of 0.20, 0.25 (for pest management purposes), 0.30 and 0.35. The current sample size raised a precision of 0.30, and an increase of the number of traps to 37 would be needed to achieve the desirable precision of 0.25. This fixed-precision sequential sampling plan for Sitophilus spp. populations in rice is demonstrated to be a useful tool in IPM tactics at rice facilities.

Problems and management of insect pests in social forestry in Nigeria

Social forestry involves the participation of the local people in the management and protection of forests and afforestation with the purpose of fostering environmental, social and rural development. The species commonly planted belong to the genera Acacia, Albizia, Artocorpus, Azadirachta, Casuarina, Celtis,Eucalyptus, Moringa, Mangifera, and Prosopis. This paper studied the current status of forest pests, by reviewing the main problems faced by these tree species commonly planted and appropriate measures to manage these pests. For instance seed pests such as Dichocrosis punctiferalis and Sitophilus spp bore fruits in the standing trees and nursery pests that cause serious damages to roots are Holotrochia consanguinea and Apogonia uniformis. Pests problem in plantations are mainly defoliators, sap suckers and xylophagous pests. Management practices to prevent these pests include behavioural and genetical methods of control, plant varietal resistance, cultural methods or ecological management, and biological control. However, access to improved breed of tree species would have a long way to reducing the incidence of pests attack in social forestry. Key words: Social forestry, insect pests problems management.

PRESERVAÇÃO DE MILHO A GRANEL COM ABAMECTIN CONTRA O ATAQUE DE Sitophilus spp. (Coleoptera – Circulionidae)

This study was carried out to test alternative products in the Sitophilus spp control. In grain stored corn were tested the products and doses: abamectin 1.0, 3.0 and 5.0 ppm; pirimifos-metil 1.0 ppm; deltamethrina 0.4 ppm + fenitrothion 7.5 ppm. The recorded results showed high efficiency to abamectin in all tested doses. With 3.0 and 5.0 ppm the abamectin showed 100% efficiency in comparison with pirimifos-metil and deltamethrina + fenitrothion.

On-farm storage studies on sorghum and chickpea in Eritrea.

On-farm storage studies were conducted in Teraemini, Ashera and Hamelmalo sub-zones in Eritrea during 2004/2005, with the objective of finding the damages caused by storage pests under farmers’ situations. The studies were conducted on chickpea and sorghum and the treatments used were sand, small grain (taff, Eragrostis tef), vegetable oil and chemical (Malathox 1%). Data were collected every month on the number of eggs, number of holes, grain damage, weight loss and germination of the grains. The major storage pests observed during the studies were bruchids (Callosobruchus chinensis L.) on chickpea. Sorghum was attacked in storage by Angoumois grain moth (Sitotroga cerealella), weevils (Sitophilus spp), confused flour beetles (Tribolium spp), saw toothed grain beetles and mites. The populations of these pests were very low in the first three months. However, after three months of storage the population of the pests in all grains and locations increased very fast and caused high damage. The highest grain damages were recorded in the untreated control (check), sand and taff treatments. The weight loss for sorghum and chickpea in the untreated control (check) were 9.17 and 27.51%, respectively. Ash, oil and chemical treatments significantly lowered grain damage and weight loss in all the studies and locations. Ash and edible oils-treated grains had low or no storage pest problems in all the study sites

Characterizing spatial distribution of trap captures of beetles in retail pet stores using SADIE ® software

The weevils, Sitophilus spp., drug store beetle, Stegobium paniceum (L.), and red flour beetle, Tribolium castaneum (Herbst) in two retail pet stores in Kansas, USA, were sampled with pitfall traps on five separate occasions before and four separate occasions after a thorough sanitation in areas with high trap captures. Trap captures of Sitophilus spp. and S. paniceum in store 1 and those of T. castaneum and Sitophilus spp. in store 2, were analyzed using the Spatial Analysis of Distance IndicEs (SADIE ®) software. Captures of Sitophilus spp. in store 1 and T. castaneum in store 2 increased immediately after sanitation, but subsequently were similar to levels before sanitation, whereas captures of S. paniceum in store 1 and Sitophilus spp. in store 2 were unaffected by sanitation. In store 1, S. paniceum trap captures were randomly distributed on all sampling occasions, while Sitophilus spp . captures were spatially aggregated immediately before and after sanitation. During the 6 months of trapping, the Sitophilus spp. trap capture centroids gradually moved northwards, and those of S. paniceum moved southwards. In store 2, trap captures of T. castaneum and Sitophilus spp. were uniformly distributed before sanitation and were predominantly spatially aggregated after sanitation. During the 6 months of trapping, trap capture centroids of both T. castaneum and Sitophilus spp. gradually moved northwards. The impact of a thorough sanitation performed once on the spatial distribution patterns of insects in the two retail stores was not consistent. Sanitation was also ineffective in reducing captures of the insect species.

Field monitoring Sitophilus zeamais and Sitophilus oryzae (Coleoptera: Curculionidae) using refuge and flight traps baited with synthetic pheromone and cracked wheat

Flight traps with open vertical baffles and refuge traps in the form of rectangular cardboard boxes were used to catch Sitophilus zeamais and S. oryzae in Kenya. Traps baited with the aggregation pheromone (Sitophilure), and for the first time traps baited with pheromone and food bait (cracked wheat), were field tested. Both traps types were effective in capturing Sitophilus spp and gave higher weevil catch when baited with pheromone and cracked wheat combined than with pheromone or cracked wheat alone. The combination of pheromone and cracked wheat had an additive effect on trap catch and not a synergistic effect as reported in earlier laboratory trials. Different pheromone loadings of 0.5, 1 and 2 mg were tested. The catch of S. zeamais in flight traps rose significantly with increasing dosage. For refuge traps, the same effect was observed although the difference between 1 mg and 2 mg was not statistically significant. The trend was for increasing S. oryzae catch with dosage, although total catches were very much lower than those for S. zeamais, and differences did not prove statistically significant. Traps placed on the floor near infested maize cribs captured significantly more Sitophilus spp than those actually placed in the cribs. Adult Sitophilus captured were sexed and in both flight and refuge traps the sex ratio was biased in favour of females even though the sex ratio of weevils from infested maize cobs, which were the source of the captured weevils, was approximately even.

Laboratory evaluation of acid-activated kaolin to protect stored paddy against infestation by stored product insects

The toxicity of acid-activated kaolin to adult populations of Sitophilus oryzae, S. zeamais, Tribolium castaneum, Cryptolestes pusillus, Oryzaephilus surinamensis and Rhyzopertha dominica was assessed by admixing the material with paddy and determining mortality at 72 hr. C. pusillus and O. surinamensis were highly susceptible to the desiccant effect, while T. castaneum and the Sitophilus spp were relatively tolerant; the susceptibility of all species to the material decreased as paddy moisture content was increased from 7.2 to 19.2%. A dose of approx. 5 g/kg considerably reduced F 1 progeny production of all the above species and of Sitotroga cerealella. Subsequent heat treatment of acid-activated kaolin had no significant effect on either its oil adsorption capacity or its toxicity to the species tested.

Synergized deltamethrin as a protectant against Sitophilus zeamais Motsch. and S. oryzae (L.) (Coleoptera: Curculionidae) on stored maize

The efficacy of deltamethrin applied to maize in combination with different rates of the synergist piperonyl butoxide (PB), was evaluated in the laboratory against Sitophilus zeamais. The test strain had been collected from maize treated with unsynergized deltamethrin in an earlier field trial and a degree of resistance was indicated in impregnated paper assays. Freshly applied deltamethrin was synergized by concentrations of PB above 0.001 mg kg −1 to a maximum of about 15 times at 2 mg kg −1, with no further improvement thereafter. However, when treated grain was stored at 30°C for up to 48 weeks the efficacy of aged treatments improved with increasing application rates of PB up to at least 16 mg kg −1. The results can be explained by breakdown of deltamethrin with concurrent breakdown of PB and consequent reduction in synergism. Application of deltamethrin at 1 mg kg −1 with PB at 8 mg kg −1 prevented F 2 progeny for 24 weeks, whereas PB at 16 mg kg −1 gave 48 weeks protection. However, impregnated paper assays showed that synergized deltamethrin was less effective against a deltamethrin-selected strain of S. zeamais and an organophosphorus-resistant strain of S. oryzae than against the test strain, and so all populations of Sitophilus spp may not be controlled by these treatments.

Evaluation of extracts of neem ( Azadirachta indica A. Juss) for the control of some stored product pests

Laboratory investigations on the activity of neem leaf and seed extracts in water or methylated spirit on Callosobruchus maculatus, Sitophilus oryzae and Cylas puncticollis were made at 27 ± 2°C and 65 ± 5% r.h.. Field trials were conducted to determine their effectiveness as protectants of cowpeas and maize in storage at 28 ± 4°C and 82 ± 7% r.h for 5 months. The results showed that the effectiveness of neem is affected by differences in insect behaviour. The extracts were more active as suppressants of C. maculatus than Sitophilus spp; there was no effect on C. puncticollis. All of the extracts tested resulted in a significant reduction in oviposition, % egg hatch and % adult emergence in C. maculatus and in adult emergence of Sitophilus. Field trials showed that the extracts mostly gave good protection to cowpea against C. maculatus for 5 months, but only moderate protection to maize against S. zeamais. Seed extracts were more effective than leaf extracts.