Maize Weevil Sitophilus Zeamais Motschulsky Research Articles

Bionomics and Management of Maize Weevil, Sitophilus zeamais Motschulsky

The maize weevil Sitophilus zeamais Motschulsky (Coleoptera:Curculionidae) is an important pest of maize in storage in term of losses caused in food quality and quantity in Nepal. Attempt made to review bionomics and management practices of this pest gleaning published literatures/papers on national and international journals, proceedings, reports, newsletter and books. The paper discusses on nomenclature, morphology, distribution, biology and ecology of maize weevil and provides prospect of using various physical, sanitary, cultural, botanical, biological and chemical control measures to manage weevil. This information is useful to personnel involved on agricultural research and development for developing location specific integrated pest management approach of this pest. Finally, it also shows importance of farmers’ awareness on pest biology and ecology, appropriate maize harvesting time, storage structures and post-harvest handling practices to reduce losses in maize storage.

Impact of Age on the Biological Activities of Sitophilus zeamais (Coleoptera: Curculionidae) Adults on Stored Maize: Implications for Food Security and Pest Management.

The present work was undertaken in three successive years in three different regions of Nigeria to study the impact of age on the postharvest biological performance of maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) adults infesting maize grain. Eight different age groups of S. zeamais adults which ranged from 1 to 56 d were used. The study assessed important parameters and was carried out using standard methods at mean temperature and relative humidity of 28.2°C and 87.5%, respectively. Results indicated that age affected bionomics of S. zeamais adult infesting maize grain in storage. The minimum age threshold for prolific oviposition in the females was 8 d. Weevils in the age groups 8-14 and 15-21 d showed highest fecundity. There was no effect of age on progeny emergence and development time for weevils younger than 36 d. Consequent upon infestation, only S. zeamais adults of ≤35 d old caused great damage and loss to grains in storage. The susceptibility of infesting weevil to cypermethrin was not greatly influenced by weevil age except at an elderly age of ≥43 d. Observations signal that weevil adults are physiologically fittest at ≤14 d old but indicate that adults of ≤35 d old pose the highest food security threat. The S. zeamais ecotype studied showed resistance to the pyrethroid insecticide at 24 h evaluation period and that also has implications for food security.

Unusual behavior of oviposition and development of Sitophilus zeamais (Coleoptera: Curculionidae) in peach and apple fruits

The maize weevil Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae) is a worldwide pest on stored products, as maize, wheat and rice grains. However, in South Brazil, these weevils have been found attacking fruits in field conditions. It was reported that adults attack fruits to feeding, but there was no information of oviposition and larval development on these hosts. Furthermore, due to monitoring apple orchards, was observed that some fruits showed distinct kind of punctures, suggesting a oviposition by these weevils. The present study reports first record an unusual behavior of S. zeamais by oviposition and larval development in peach and apple fruits. The study was conducted in laboratory conditions (temperature: 25 ± 1 °C, RH: 70 ± 10% and photophase of 14 h). Peach and apple fruits were offered to S. zeamais females. The oviposition and duration of immature stages in peach were measured in fruits and in corn grains, used as control observation. The oviposition and larval development occurred in peach and apple fruits, with a development until to adult. The average of egg-to-adult was 47.4 d in peach and and 45.1 d apple fruits, respectively, while in corn grains, its natural host, the duration was 38.2 d. These results show that the damage caused by S. zeamais in peach and apple fruits may be due to oviposition and the development of immature stages. So, the novelty is in demonstrating that the maize weevil does not just feed as an adult opportunistically on the fruits, but can complete a full life cycle using fresh fruits.

Toxicity of an Annonin-Based Commercial Bioinsecticide Against Three Primary Pest Species of Stored Products.

The effects of a bioinsecticide formulation based on extract of Annona squamosa L. (Annonaceae) containing 10,000mgL-1 of acetogenin annonin as the main active ingredient were investigated against three primary pest species of stored grains in Brazil [maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), Mexican bean weevil Zabrotes subfasciatus (Boheman) (Coleoptera: Chrysomelidae: Bruchinae), and cowpea weevil Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae: Bruchinae)] by means of residual contact bioassays. In a concentration-dependent manner, the annonin-based commercial bioinsecticide caused significant adult mortality of C. maculatus (LC50=6890μLkg-1), S. zeamais (LC50=2781μLkg-1), and Z. subfasciatus (LC50=2120μLkg-1) after 120h of residual contact exposure. In addition to acute toxicity, the tested bioinsecticide also promoted a significant reduction of the number of eggs laid by females of C. maculatus (EC50=5949.7μLkg-1) and Z. subfasciatus (EC50=552.7μLkg-1). Moreover, the bioinsecticide significantly reduced the number of emerged insects (F1 generation) of C. maculatus (EC50=2763.0μLkg-1), S. zeamais (EC50=1380.8μLkg-1), and Z. subfasciatus (EC50=561.5μLkg-1). The bioinsecticide also reduced the percentage of damaged grains for the three pest species studied, and its grain-protectant properties are comparable to or superior in efficacy in relation to a diatomaceous earth-based insecticide (Insecto® at 1000mgkg-1) used as a positive control. Thus, this standardized formulation has promising bioactivity against stored insect species and can be a useful component for IPM of stored grains in Brazil and elsewhere.

Fine Structure and Sensory Apparatus of the Mouthparts of the Maize Weevil,Sitophilus zeamaisMotschulsky (Coleoptera: Curculionoidea: Dryophthoridae)

The maize weevil Sitophilus zeamais Motschulsky is one of the most serious stored-product pests worldwide. It causes significant damage and major post-harvest losses in global production as a result of adults and larvae feeding on stored grains and contaminating food products. The fine structural morphology of mouthparts, including the distribution of sensilla in adult S. zeamais , was observed using a scanning electron microscope. The mandibulate mouthparts are situated at the tip of the long rostrum. The sclerotized mandibles are irregular, serving as pincers. The maxillae are bilaterally flattened and lay almost perpendicular to the segmented venter, situated in longitudinal clefts with a four-segmented palp on each side of the labium. The cardo, stipes, palpifer, lacinia, and galea are described in detail. The tongue-like labium is considerably specialized with a pair of three-segmented palps. Four types of sensilla basiconica occur in the distal cavity of the maxillary palp and digitiform sensilla are located on the distal maxillary segment. Two types of sensilla basiconica with a 4 + 3 arrangement are present in the distal cavity of the labial palp, whereas a kind of sensilla basiconica is present at the base of the labial palp. The evolution of the mouthpart morphology and the putative functional significance of their sensilla are discussed, providing insight into the feeding mechanism.

Locomotor behavior of Sitophilus zeamais populations under sublethal ozone exposure

Insects exhibit diverse behavioral responses under insecticide exposure. However, such responses have been neglected in toxicological studies. The purpose of this work was to evaluate the influence of sublethal concentrations of ozone on the locomotor behavior of populations of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Additionally, respiration rate and body mass were also evaluated. The behavioral characteristics evaluated were distance traveled, resting time, and walking velocity of males and females, along with flight initiation for non-sexed insects. Ozone concentrations of 0, 30, 40, 50, and 60 ppm were established for the Amambay population and ozone concentrations of 0, 50, 75, 100, 125, and 150 ppm for the Sao Joao population of S. zeamais. The walking activity of the Amambay insect population decreased with increasing ozone concentration. In contrast, the walking activity of the Sao Joao population did not vary with ozone concentration. At least one of the walking characteristics is correlated with the respiration rate and body mass, indicating an association of increased respiration rate and body mass with reduced walking activity. In general, the behavioral response to ozone was population dependent. The reduction in walking activity of the S. zeamais populations under sublethal ozone exposure might limit the insect’s ability to escape its effects. These results implicate in a low risk of resistance evolution in a short term, indicating that ozone is a potential option to control pest insects of stored products.

Cytogenetic analyses using C-banding and DAPI/CMA3 staining of four populations of the maize weevil Sitophiluszeamais Motschulsky, 1855 (Coleoptera, Curculionidae).

Cytogenetic data avalaible for the maize weevil Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae), one of the most destructive pests of stored cereal grains, are controversial. Earlier studies focused on single populations and emphasized chromosome number and sex determination system. In this paper, the karyotypes of four populations of Sitophilus zeamais were characterized by conventional staining, C-banding and sequential staining with the fluorochromes chromomycin-A3/4-6-diamidino-2-phenylindole (CMA3/DAPI). The analyses of metaphases obtained from the cerebral ganglia of last instar larvae and the testes of adults showed that the species had 2n = 22 chromosomes, with 10 autosomal pairs and a sex chromosome pair (XX in females and Xyp in males). Chromosome number, however, ranged from 2n = 22 to 26 due to the presence of 0–4 supernumerary chromosomes in individuals from the populations of Viçosa, Unai and Porto Alegre. With the exception of the Y chromosome, which was dot-like, all other chromosomes of this species were metacentric, including the supernumeraries. The heterochromatin was present in the centromeric regions of all autosomes and in the centromere of the X chromosome. The B chromosomes were partially or totally heterochromatic, and the Y chromosome was euchromatic. The heterochromatic regions were labeled with C-banding and DAPI, which showed that they were rich in AT base pairs.

Insecticidal activity of Laurelia sempervirens (Ruiz & Pav.) Tul. essential oil against Sitophilus zeamais Motschulsky

The maize weevil Sitophilus zeamais Motschulsky is a worldwide key pest of stored products. Usually contact insecticides or fumigants are used against it, but problems as toxic residues, human intoxications, and resistance have triggered the search for alternative control methods as the use of essential oils. The objective of this research was to assess under laboratory conditions, the insecticidal properties of Laurelia sempervirens (Ruiz & Pav.) Tul. essential oil against S. zeamais. In contact toxicity bioassay assessed treatments were 0 (control), 1.25, 2.5, 5.0, 10, 20, and 40 mL essential oil kg-1 grain and 0 (control), 25, 50, 75, 100, 125, 150, and 175 μL essential oil L-1 air in fumigant toxicity tests. The highest toxicity by contact activity was reached by concentrations higher than 10 mL essential oil kg-1 grain (100% mortality). The same treatments totally inhibit F1. The dose of 175 μL essential oil L-1 air showed a significant toxicity by fumigant activity causing 72.5% of dead insects. The other treatments did not surpass 5% mortality. In offspring effect (F1) bioassay, all treatments had an insect emergence significantly lower than the control but concentrations equal or higher than 10 mL essential oil kg-1 grain prevented the emergence of F1 during the 7 wk of bioassay. The residual effect of contact toxicity remained by 15 d. The treatments based on essential oil lead to a weight grain loss lower than control and germination was not affected. All assessed treatments showed repellent effect. The essential oil of L. sempervirens has promissory perspectives to maize weevil control.

Desiccation resistance and water balance in populations of the maize weevil Sitophilus zeamais

Water balance is a challenge for insects due to their small size and body with high surface area-to-volume ratios, and it is particularly important for insects that inhabit dry environments, such as stored grains, and warm climates. This subject has been curiously neglected in stored product insects, including the maize weevil Sitophilus zeamais Motschulsky, were broad population differences have been reported with management consequences. Here, we assessed variation in desiccation resistance and water balance among three strains of the maize weevil exhibiting differences in body mass. The survival of male and female weevils from three strains was therefore assessed at relative humidities ranging from 0 to 100%, in which their water content and water loss were also assessed. The effect of insect aggregation (1–25 insects per group) on water balance was also assessed, as was the water gain by the drinking of free water and drinking preference when exposed to insecticide-contaminated water. The median survival time (LT50) of individual insects increased with relative humidity and varied significantly among the weevil strains. The larger strain exhibited 60–80% higher LT50 at 50% relative humidity (r.h.) and above, with little difference between strains at 0% r.h. Heavier weevils exhibited higher water content and lower overall rates of water loss; these qualities made heavier weevils more resistant to dehydration. Larger groups of weevils facilitate water retention in individual insects. Weevils actively drink water to achieve favorable water balance when dehydrated, which is a major source of water intake. Under dehydration, weevils in general were not able to discriminate between insecticide-contaminated and uncontaminated water. However, females of the insecticide-susceptible strain avoided contaminated water.

Ar-turmerone from Curcuma longa (Zingiberaceae) rhizomes and effects on Sitophilus zeamais (Coleoptera: Curculionidae) and Spodoptera frugiperda (Lepidoptera: Noctuidae)

Turmeric, Curcuma longa L. (Zingiberaceae) has well-known insecticidal and repellent effects on insect pests, but its impact on the Maize weevil Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae) and the fall armyworm Spodoptera frugiperda J.E. Smith, 1797 (Lepidoptera: Noctuidae) is unknown. In this study, we evaluated the insecticidal and repellent effects of ar-turmerone, extracted from rhizomes of C. longa, on the S. zeamais and S. frugiperda. Individuals of S. zeamais died after six days of contact with ar-turmerone at 1% (mm−1), while individuals of S. frugiperda showed a 58% mortality rate after ingestion of this compound at 1% (mv−1). The width of head capsule, and length and weight of body of surviving S. frugiperda caterpillars exposed to ar-turmerone were 60.0, 59.6 and 93.8% lower than those of control caterpillars, respectively. Dry weight of ingested food, feces produced, weight gain and dry weight of food assimilated and metabolized by surviving S. frugiperda caterpillars were lower with artificial diet with ar-turmerone. Hatching of caterpillars from newly laid, 1- or 2-day-old S. frugiperda eggs was 48.6, 14.2 and 48.5%, respectively. Ar-turmerone is highly toxic to S. zeamais and S. frugiperda at low doses.

Potential of Olax zeylanica (Olacaceae) as a botanical insecticide for the control of the Maize Weevil Sitophilus zeamais Motschulsky

The possible use of leaf powder of Olax zeylanica in managing the maize weevil, Sitophilus zeamais was investigated in the present study. Mortality of one week old adults was obtained for five different doses each for their insecticidal effect (1.0, 2.0, 3.0, 5.0 and 7.5g) and fumigation toxic activity (2.0, 3.0, 5.0, 7.5, 10.0g) separately. In each bioassay, the mortality was recorded after 3, 6, 9, 12, 18 and 24 hours after they were exposed to different doses of the plant powder. The results of both bioassays revealed that the leaf powder of this plant elicited a very high insecticidal activity as well as fumigation toxic activity in S. zeamais weevils. Mortality effect of the powders on the weevils was found to be dose and time dependent. The observations indicated that the adult mortality increased with the increase of the exposure time and the dose. No mortality was observed 3 hours after the exposure of weevils to leaf powder at all doses. A high mortality rate was observed after 9 hours of exposure with all doses except for the lowest and a 100% mortality was recorded with 7.5g after 24 hours. Fumigation toxicity of plant powder against the weevils also gave similar results where no weevil deaths were observed at all doses of leaf powder after 3 hours of exposure. At the highest dose of 10.0g, 98% mortality was observed after 24 hours. The overall results imply the strong possibility of using leaves of Olax zeylanica as a potent bio-insecticide in protecting maize grains from S. zeamais infestations.

Does cypermethrin affect enzyme activity, respiration rate and walking behavior of the maize weevil (Sitophilus zeamais)?

Insecticides cause a range of sub-lethal effects on targeted insects, which are frequently detrimental to them. However, targeted insects are able to cope with insecticides within sub-lethal ranges, which vary with their susceptibility. Here we assessed the response of three strains of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) to sub-lethal exposure to the pyrethoid insecticide cypermethrin. We expected enzyme induction associated with cypermethrin resistance since it would aid the resistant insects in surviving such exposure. Lower respiration rate and lower activity were also expected in insecticide-resistant insects since these traits are also likely to favor survivorship under insecticide exposure. Curiously though, cypermethrin did not affect activity of digestive and energy metabolism enzymes, and even reduced the activity of some enzymes (particularly for cellulase and cysteine-proteinase activity in this case). There was strain variation in response, which may be (partially) related to insecticide resistance in some strains. Sub-lethal exposure to cypermethrin depressed proteolytic and mainly cellulolytic activity in the exposed insects, which is likely to impair their fitness. However, such exposure did not affect respiration rate and walking behavior of the insects (except for the susceptible strain where walking activity was reduced). Walking activity varies with strain and may minimize insecticide exposure, which should be a concern, particularly if associated with (physiological) insecticide resistance.

Resistance of three-way cross experimental maize hybrids to post-harvest insect pests, the larger grain borer ( Prostephanus truncatus) and maize weevil ( Sitophilus zeamais)

The larger grain borer Prostephanus truncatus Horn and the maize weevil Sitophilus zeamais Motschulsky are important pests of stored maize in the tropics, particularly where maize is stored on-farm with little control of moisture content and without use of pesticides. This study was undertaken to determine level of resistance among new experimental maize hybrids against P. truncatus and S. zeamais. Out of the 54 experimental hybrids tested, eight hybrids were resistant, six were susceptible and the remaining 40 hybrids were moderately resistant. Five hybrids showed considerable reduction in losses for both P. truncatus and S. zeamais (CKPH08013, CKPH08021, CKPH08003, CKPH08004 and CKPH08009), suggesting that they contained genes that confer resistance to the two pests. Low grain weight loss, powder production and low insect multiplication on resistant grains reduce the negative impact of the two beetle pests. Therefore, host plant resistance can be used as a vital component of an integrated pest management strategy against P. truncatus and S. zeamais.

Face or flee? Fenitrothion resistance and behavioral response in populations of the maize weevil, Sitophilus zeamais

Insect survival in the presence of contact insecticides may be through physiological mechanisms or avoidance of contact with the compound. Curiously, although the first alternative is the object of frequent attention, the second is often neglected, but both may lead to insecticide resistance. Preliminary evidence for both physiological and behavioral resistance to pyrethroids has been obtained for a few strains of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Here we carried out a more comprehensive survey using 15 populations of S. zeamais, by examining a long-used but relatively little studied organophosphate – fenitrothion, recording not only physiological resistance, but also the behavioral responses to exposure. Physiological resistance to fenitrothion among populations of S. zeamais reached low to moderate levels (ranging from 0.9 to 14.1× at the LC 50), an increase in resistance levels compared with previous studies. Fenitrothion-induced behavioral avoidance varied among populations, particularly regarding insecticide irritability (i.e., avoidance after contact with fenitrothion), but the behavioral responses observed were mainly stimulus-independent. However, there was no correlation between physiological and behavioral resistance to fenitrothion in S. zeamais populations. Both survival strategies to fenitrothion – facing or fleeing the insecticide exposure, were observed and may co-occur in a single population, emphasizing the need of assessing both responses and their relative importance in designing management programs against stored-product insects.

Flight take-off and walking behavior of insecticide-susceptible and – resistant strains of Sitophilus zeamais exposed to deltamethrin

Insects have evolved a variety of physiological and behavioral responses to various toxins in natural and managed ecosystems. However, insect behavior is seldom considered in insecticide studies although insects are capable of changing their behavior in response to their sensory perception of insecticides, which may compromise insecticide efficacy. This is particularly serious for insect pests that are physiologically resistant to insecticides since insecticide avoidance may further compromise their management. Locomotion plays a major role determining insecticide exposure and was, therefore, considered in investigating the behavioral responses of male and female adult insects from an insecticide-susceptible and two insecticide-resistant strains of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), a major pest of stored cereals. Different dose-dependent behavioral responses were expected among strains with behavioral resistance less likely to occur in physiologically resistant insects since they are able to withstand higher doses of insecticide. The behavioral responses to deltamethrin-sprayed surfaces differed among the maize weevil strains. Such responses were concentration-independent for all of the strains. Stimulus-independent behavioral resistance was unrelated to physiological resistance with one resistant strain exhibiting higher rates of flight take-off and the other resistant strain exhibiting lower flight take-off. Female mobility was similar for all strains, unlike male mobility. Males of each strain exhibited a pattern of mobility following the same trend of flight take-off. Behavioral patterns of response to insecticide are, therefore, variable among strains, particularly among insecticide-resistant strains, and worth considering in resistance surveys and management programs.

Efficacy of Piper guineense (Schum & Thonn) seed extract against maize weevil, Sitophilus zeamais (Motschulsky) as influenced by different extraction solvents

The seed extract of black pepper Piper guineense Schum & Thonn was evaluated for its biological activity against the maize weevil Sitophilus zeamais Motschulsky at 30°C, 65 ± 2% R.H and 12:12-h light:dark regimes in the laboratory. The different solvents used for the extraction were acetone, ethanol, n-hexane, petroleum ether (60:80) and distilled water at 0.3% dosage level. The acetone extract had the highest toxicity (100%), while the control showed no toxicity at 28 days post treatment. All of the treatments significantly reduced adult emergence and grain damage compared with the control. Grain germination with the solvents was significantly higher than with the aqueous extract (49%), which was significantly superior to the control (39%). Piper guineense extract with the different organic solvents caused acute mortality in S. zeamais adults.

Partial characterization of glutathione S-transferases in pyrethroid-resistant and -susceptible populations of the maize weevil, Sitophilus zeamais

Glutathione S-transferases (GSTs) from a susceptible (Sete Lagoas) and two pyrethroid-resistant populations (Jacarezinho and Juiz de Fora) of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) were characterized through in vitro colorimetric assays. GSTs showed higher activity peaks at pH 9.0 and 30 °C. The K m -values for GSTs were similar among the populations except for the resistant population from Juiz de Fora, which was about two-fold higher than the susceptible population from Sete Lagoas when using 1-chloro-2,4-dinitrobenzene (CDNB) as substrate (and a fixed concentration of reduced glutathione—GSH). The V max of this same resistant population was also over two-fold higher than that of the pyrethroid-susceptible population when CDNB and GSH were used as substrates. The resistant population from Jacarezinho also had a slightly, but significantly, higher V max than the susceptible population when using these two substrates. However, there were no significant differences among the kinetic parameters of GSTs from the maize weevil populations when DCNB and GSH were used as substrates. These results provide evidence of the involvement of enhanced GST activity as an additional pyrethroid-resistant mechanism in at least some maize weevil populations from Brazil.