Weevil Populations Research Articles

Spatiotemporal dynamics of a palm weevils' outbreak and susceptibility of peach palm (Bactris gasipaes Kunth) landraces in a germplasm bank in southwestern Colombia

AbstractThe palm weevils Rhynchophorus palmarum and Dynamis borassi are prominent pest species in peach palms and coconut in Colombia. Nevertheless, knowledge of the population dynamics of these weevil species in the neotropical region is still scarce. In this study, we systematically sampled these weevils over 2 years using pheromone traps (1 trap ha−1) in an experimental peach palm plantation under heavy weevil infestation in southwestern Colombia. Additionally, we censused the palms in a portion of the plantation (a peach palm germplasm bank) before and after the weevil monitoring. We analysed the data to elucidate sex‐specific temporal and spatial patterns of both R. palmarum and D. borassi in a 19.13 ha area. Furthermore, we sought to detect peach palm landraces within the germplasm bank susceptible and resistant/tolerant to the weevil attack. During periods when insect populations were high, we observed that R. palmarum consistently outnumbered D. borassi. Specifically, we found that R. palmarum reached up to 80 insects trap−1 month−1, while D. borassi only reached around 30 insects trap−1 month−1 during the peak months. However, both species exhibited synchronous population peaks, which were not related to rainfall or temperature but rather to the phenological stage of the peach palm. Furthermore, the weevils had a highly aggregated spatial pattern; insect catchments were more prolific in areas where the landraces Nariño and Risaralda were sown. Moreover, the census evidenced that these two landraces were the most affected. Contrarily, weevil capture was overall low around the Guaviare landrace, this was the only landrace that exhibited an increase in stipes between census years. Our results highlight that complementary control strategies are needed to counteract sudden weevil population outbreaks, as pheromone traps are a good tool for monitoring but not for effective control. Furthermore, more importantly, a peach palm breeding programme based on the identified genotypes should be the basis for the integrated pest management of palm weevils.

The importance of long‐term post‐release studies in classical biological control: Insect–plant monitoring and public awareness of water hyacinth management (Pontederia crassipes) in Dique Los Sauces, Argentina

AbstractSeveral components of classical biological control (CBC) programmes are necessary to assess the success of the management strategy (e.g., post‐release monitoring) and also help prevent reintroductions or resurgences of invasive species (e.g., public awareness). Water hyacinth, Pontederia (= Eichhornia) crassipes (Mart.) Solms (Pontederiaceae) is an aquatic plant naturally distributed in the north‐eastern region of the Del Plata basin in Argentina. In the 1960s it was introduced into the Dique Los Sauces reservoir located outside of its native range in La Rioja Province, in western Argentina, where it became invasive. The natural enemy, Neochetina bruchi Hustache (Coleoptera: Curculionidae), was intentionally introduced in 1974 to control the weed. To assess the success of this CBC programme, a long‐term post‐release study was conducted. Between 1965 and 2023, we monitored plant coverage, estimated N. bruchi densities, and quantified the associated damage by reanalysing previously published data and incorporating new sampling. We also conducted an online survey to analyse public knowledge and perception about this programme. Water hyacinth coverage fluctuated from its first record in 1965 (maximum coverage 90%) until the control of germinated plants (coverage 0%) in 2018. The plant decline was accompanied by an increase in the weevil population. In our survey, out of 325 respondents only a small group of mostly middle‐aged and elderly people knew that the restoration had been achieved through a management strategy and even fewer were aware of the biocontrol approach taken. Respondents who had a positive approach to biological control were more aware of the management plan than respondents who had neutral or negative opinions. Neochetina bruchi has played a key factor in the control of P. crassipes. The intrinsic dynamics of these populations, the dormant seed bank, and the lack of public awareness support the need for long post‐release evaluations including outreach campaigns to make a sustainable successful management programme.

Source tracing of Anthonomus grandis captured in areas of the USA where the species had previously been eradicated

Anthonomus grandis Boheman (Coleoptera: Curculionidae) is comprised of two subspecies: the boll weevil (A. g. grandis) and the thurberia weevil (A. g. thurberiae). The thurberia weevil is generally regarded as a non-pest variant of the species, whereas the boll weevil is an important economic pest of commercial cotton. In the USA, a nationwide eradication program has been largely successful against the boll weevil, but reintroductions of eradicated zones remain a threat. In 2015, A. grandis was trapped in the functionally eradicated Winter Garden growing region in Texas, where it had not been found since 2012. Weevils established in the area and triggered a multi-year, multi-million-dollar mitigation effort. In 2017, the species was trapped in Hidalgo County, New Mexico, another area where it had been previously eradicated. In this study, we obtained specimens from both trapping events and used double digest restriction site-associated DNA sequencing to obtain genetic data in homology with previously published A. grandis population genetic data. We conducted source tracing to match the captured weevils to previously described populations to determine a likely source population. We also compared the accuracy of the approach to other diagnostic methods currently used by the United States Department of Agriculture. The results suggested that a small founder population of weevils dispersed from the Lower Rio Grande Valley population in southern Texas and northern Tamaulipas and established in the Winter Garden. In Hidalgo Co., NM, the weevils were found to be genetically indistinct from non-pest populations of thurberia weevil associated with Arizona wild cotton (Gossypium thurberi). Thurberia weevils in Arizona remain unlikely to threaten commercial growers. Improved rapid diagnostic tools may be desirable to enable better assessment of trap captures and allow for a reduction in the application of mitigation efforts when the non-pest variant is identified.

Diatomaceous earth against Ecuadorian populations of the maize weevil (Sitophilus zeamais)

Diatomaceous earth (DE) is an inert dust derived from unicellular algae, which is effectively used as an insecticide. The DE efficacy has been recognized against a range of stored grain insects including the maize weevil (Sitophilus zeamais, Motschulsky, 1885). However, little is known about the effect of DE among maize weevil populations exposed to different doses, particularly regarding its potential effects on mortality, repellence, progeny emergence, and grain consumption. Thus, we assessed DE (83.97% SiO2) effects of three Ecuadorian maize weevil populations (Buena Fe, Mocache, Quevedo) exposed to different DE doses (0, 1, 3, 5 g DE/kg of maize). As expected, the three DE doses were able to effectively control the insects (P = 0.05) with the median survival times (LT50) ranging from 5 to 9 days (120.00–216.00 h). No DE repellence was detected in the three maize weevil population, regardless of the dose used suggesting that DE is not recognized by the adult weevils. The DE doses applied against maize weevil led to reduction on the progeny production of S. zeamais (χ2 = 235.77, df = 1, P < 0.001) and compromised their grain consumption (F1,174 = 20.65, P < 0.001). However, no differences were found among the three weevil populations. These findings reinforce the use of DE as an alternative in management programs for S. zeamais populations.

Male inflorescences, natural enemies, and climate as biotic and abiotic factors on population Elaeidobius kamerunicus at three soil types

Pollination determines pollinating weevils in oil palm. Abiotic and biotic factors can influence population pollinator weevils. An experiment was carried out in PT. Sawit Sumbermas Sarana, Tbk. The object of research is to analyze the influence of male inflorescences, natural enemies, and climate on pollinating weevils population at clay, sandy, and peat soil types. The research method used a sampling design. Observation variables were conducted every two weeks for the availability of anthesis male inflorescences, natural enemies, and climate. Davis Vantage Pro 2 was used to measure the climate. The results showed the population of pollinator weevils was significant (p<0.05) influence on male inflorescence. The anthesis male inflorescence per ha increases as the population of pollinator weevil increases. Climate and natural enemies such as Rattus sp., Gasterachanta sp., Argiope sp., Sycanus sp., and Cosmolestes sp., have insignificant influences on pollinating weevils population. Male inflorescence was biotic factor as the source of food for pollinator weevils on clay, sandy, and peat soil types.

Optimizing Sampling Technique Parameters for Increased Precision and Practicality in Annual Bluegrass Weevil Population Monitoring

The annual bluegrass weevil (ABW), Listronotus maculicollis (Kirby), a significant pest of short-mown turfgrass in eastern North America, has developed widespread insecticide resistance because of excessive synthetic insecticide use. The proper monitoring of this pest may reduce insecticide applications in time and space. This study evaluated three sampling methods (soap flushing, vacuuming, and mowing) in golf course greens and fairways for monitoring adult ABW. Soap flushing was the most efficient method, especially with an 0.8% solution in two portions of 500 mL, extracting over 75% of the adults, and the extraction efficiency was not affected by the temperature or time of day. Vacuuming was more effective for recovering adult ABWs on greens (4–29% extracted) than on fairways (2–4%) but was not affected by the time of day. The extraction of adult ABWs in mower clippings was significantly affected by mowing height (higher recovery from greens versus fairways), and the efficiency decreased with the temperature. Adding a brush to the mower increased adult removal (from 15% to 24%) in greens at higher temperatures (18–25 °C); 70% of adults recovered in the clippings were unharmed. Overall, our findings suggest that soap flushing should be the preferred method for monitoring adult ABWs, and vacuuming might be a viable alternative for greens.

Retrospective use of integrative taxonomy in classical biological control: The unintentional introduction of the weevil Rhinusa dieckmanni to North America

A seed-feeding weevil introduced to North America (NA) as a biological control agent of the invasive toadflax Linaria dalmatica (L.) Mill., identified then as Gymnetron antirrhini “Dalmatian host race” and subsequently confirmed as established, was revealed through our study to be a separate species, i.e., Rhinusa dieckmanni (Behne) (Coleoptera: Curculionidae). This weevil species was presumed to be endemic in its native range, with a distribution restricted to Mount Rila in southwestern Bulgaria. We conducted a comprehensive study of seed-feeding weevils associated with L. dalmatica, L. dalmatica ssp. macedonica (Griseb.) D.A. Sutton, L. genistifolia (L.) Mill., and L. grandiflora Desf. across a broad geographic area of their native range. Those results revealed that all four host plants were used by R. dieckmanni and thus the native geographic range of the species is wider than expected, encompassing the Balkans and the Anatolian Plateau. Our observations suggest that phenotypes of this weevil are highly variable and dependent on the seed capsule size of the Linaria host population. The haplotype network based on mitochondrial COII, 16S genes, and nuclear EF 1-α gene genealogy confirmed the conspecific nature of geographically distant weevil populations, that is, R. dieckmanni phenotypes utilizing L. genistifolia, L. dalmatica, and L. grandiflora for larval development. Specimens collected from L. dalmatica in the northwestern USA shared the same haplotypes as samples from L. dalmatica ssp. macedonica in southwestern North Macedonia, supporting the known introduction history of the North American population. Females from these populations have relatively short rostrums, which may limit their reproductive success on North American invasive L. dalmatica with larger seed capsules.

Factors Affecting Pollination and Pollinators in Oil Palm Plantations: A Review with an Emphasis on the Elaeidobius kamerunicus Weevil (Coleoptera: Curculionidae).

Pollination is crucial for oil palm yield, and its efficiency is influenced by multiple factors, including the effectiveness of Elaeidobius kamerunicus weevils as pollinators in Southeast Asia. Weevils transfer pollen between male and female flowers, leading to successful fertilization and fruit development, which contributes to higher oil palm yields and increased production of valuable oil. Understanding and conserving the weevil population is important for sustainable oil palm cultivation practices. The interaction between pollinators, including weevils, and environmental factors is complex, involving aspects such as pollinator behavior, abundance, diversity, and effectiveness, which are influenced by weather, landscape composition, and pesticide use. Understanding these interactions is critical for promoting sustainable pollination practices, including effective pest management and maintaining optimal pollinator populations. This review discusses various abiotic and biotic factors that affect pollination and pollinators in oil palm plantations, with a particular focus on weevils as primary pollinators. Factors such as rainfall, humidity, oil palm species, temperature, endogamy, parasitic nematodes, insecticides, predators, and proximity to natural forests can impact the weevil population. Further research is recommended to fill knowledge gaps and promote sustainable pollination practices in the oil palm industry.

Biocontrol of Maize Weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), in Maize over a Six-Month Storage Period.

Food security is contingent upon increasing crop yields but also upon reducing crop losses to post-harvest pests and diseases. Weevils are particularly important agents of post-harvest losses in grain crops. A long-term evaluation of a biocontrol agent, Beauveria bassiana Strain MS-8, at a single dose of 2 × 109 conidia kg-1 of grain was formulated in kaolin as a carrier at levels of 1, 2, 3, and 4 g kg-1 of grain and screened against the maize weevil, Sitophilus zeamais. After six months, the application of B. bassiana Strain MS-8 at all levels of kaolin significantly reduced the maize weevil populations compared to the untreated control (UTC). The best control of maize weevil was observed in the first 4 months after application. Strain MS-8 applied in a kaolin level of 1 g kg-1 performed the best, resulting in the lowest number of live weevils (36 insects/500 g of maize grain), the lowest level of grain damage (14.0%), and the least weight loss (7.0%). In the UTC the number of live insects was 340 insects/500 g of maize grain, the level of grain damage was 68.0%, and weight loss was 51.0%.

Paternity Analyses for the Planning of SIT Projects against the Red Palm Weevil

The red palm weevil Rhynchophorus ferrugineus is an invasive pest from southeastern Asia and Melanesia that has spread widely across the Middle East and the Mediterranean Basin over the last 30 years. Its endophagous larvae cause huge amounts of damage to several palm tree species from the Arecaceae family. Many of these palms are economically important for agricultural and ornamental purposes. Therefore, a lot of attention has recently been focused on studying this species with the aim of identifying sustainable and effective eradication strategies. Sterile insect techniques are biological control strategies that are currently being investigated for their potential to eradicate this pest in selected invasion areas. Mating system features (e.g., polyandry and related features) can affect the success and suitability of these approaches. The main goal of this research was to assess the performance of a previously developed microsatellite panel in terms of the paternity assignment of progeny from laboratory mating experiments. Using a simulation approach, we evaluated the reliability of the microsatellite markers in the paternity tests both in complex laboratory experiment scenarios and on the progeny of wild-caught gravid females to help future studies on the RPW mating system. As a case study of the simulation results, we performed two double-mating experiments, genotyped the progeny and estimated the P2 values to compare to the expected progeny genotypes according to the crossing scheme of each experiment. The results of our simulations on laboratory experiments showed that it was possible to carry out paternity assignments for all progeny with reliable statistical confidence using our 13 microsatellites set. On the contrary the low genetic variability measured in red palm weevil populations in invaded areas made the resolution power of our loci too low to carry out paternity analyses on natural populations. Results of laboratory crossing were completely congruent with the expectations from the Mendelian laws.

Genetic diversity and structure of Callosobruchus maculatus populations in the different agro-ecological zones of Senegal

The objective of this study is to determine the diversity and genetic structure of cowpea weevil populations in the different agro-ecological zones of Senegal. Thus, to achieve this objective, individuals of Callosobruchus maculatus from localities in each zone were used, after sampling and massive breeding. The sequenced gene is Cyt-B. The results showed high haplotypic diversity (0.901 ±0.00033) and low nucleotide diversity (0.010 ±0.0000003). These diversities studied by agro-ecological zone show that the Casamance zone has the greatest haplotypic diversity (0.901; P&gt;0.05) while the eastern Senegal zone has the lowest value (0.439; P&gt;0.05). The nucleotide diversity is lower in the Sylvo-pastoral zone (0.00112; P&lt;0.05) and higher in the Casamance zone (0.01052; P&lt;0.05). The genetic structuring shows that the Senegal River Valley-eastern Senegal zone couple is more differentiated [FST(Fixation index)]=0.70687; P&lt;0.05) and the Casamance-Groundnut Basin zone couple is less differentiated (FST=0.21248; P&lt;0.05). The greatest genetic distance was found between the Sylvo-pastoral zone and the River Valley and the smallest between the eastern Senegal zone and the River Valley. However, a significant genetic variation within the populations was noted (64.93%). Overall we have a low level of diversity and weakly structured populations except those of Tamba and Fouta. A slight influence of the zones was also noted.

Development of Nuclear DNA Markers for Applications in Genetic Diversity Study of Oil Palm-Pollinating Weevil Populations.

The oil palm-pollinating weevil (Elaeidobius kamerunicus Faust) was introduced from Cameroon, West Africa, to Malaysia in 1981, and subsequently, to other oil palm-growing countries as well. This study aims to develop a set of robust E. kamerunicus-specific nuclear DNA markers to directly assess the genetic diversity of the weevil populations. A total of 19,148 SNP and 223,200 SSR were discovered from 48 weevils representing three origins (Peninsular Malaysia, Sabah, and Riau) using RAD tag sequencing. Subsequent filtering steps further reduced these to 1000 SNP and 120 SSR. The selected 220 SNP exhibited a polymorphism information content (PIC) of 0.2387 (±0.1280), and 8 SSR had the PIC of 0.5084 (±0.1928). These markers were found to show sufficient polymorphism, making it possible to assign 180 weevils into three major clusters from Ghana, Cameroon, and Southeast Asia (mainly in Malaysia and Indonesia). These DNA markers successfully confirmed the Cameroon origin of the Southeast Asian cluster. However, the presence of null alleles in the SSR markers, due to limited flexibility of the probe design on the short RAD tags, led to an underestimation of heterozygosity within the populations. Hence, the developed SNP markers turned out to be more efficient than the SSR markers in the genetic diversity assessment of the E. kamerunicus populations. The genetic information provides useful insight into developing guidelines for the genetic monitoring and conservation planning of E. kamerunicus.

A novel picorna-like virus identified in the cotton boll weevil Anthonomus grandis (Coleoptera: Curculionidae).

The cotton boll weevil (CBW; Anthonomus grandis; Coleoptera: Curculionidae) is considered the major insect pest of cotton, causing considerable losses in yield and fiber quality. An increase in the boll weevil population due to increasingly inefficient chemical control measures is of great concernamong cotton producers. The absence of conventional or transgenic cultivars with minimal resistance to CBW has stimulated the search for new molecular and biological tools for efficient control of this insect pest. In this study, we used a metagenomic approach based on RNA deep sequencing to investigate the presence of viruses and coding viral RNA in apparently healthy native adult CBW insects collected from cotton crops in Mato Grosso state, Brazil. Using an Illumina HiSeq 2000 paired-end platform, 138,798 virus-related reads were obtained, and a consensus sequence of a putative new virus, 10,632 nucleotides in length, was assembled. The sequences of the 5' and 3' untranslated regions (UTRs) were determined by rapid amplification of cDNA ends (RACE), followed by Nanopore sequencing. The complete genome sequence included a 5'-UTR (1,158 nucleotides), a 3'-UTR (561 nucleotides), and a single ORF of 8,913 nucleotides encoding a large polyprotein. Sequence analysis of the putative polyprotein showed several regions with high sequence similarity to structural and non-structural proteins of viruses of the family Iflaviridae. Pairwise alignments of polyprotein amino acid sequences showed the highest sequence identity (32.13%) to a partial polyprotein sequence of a putative iflavirus (QKN89051.1) found in samples from wild zoo birds in China. Phylogenetic analysis based on full polyprotein sequences of different iflaviruses indicated that this new picorna-like virus is most closely related to iflaviruses found in lepidopteran insects, and it was therefore tentatively named "Anthonomus grandis iflavirus 1" (AgIV-1). This is, to our knowledge, the first complete viral genome sequence found in CBW, and it could provide a basis for further studies about the infectivity and transmission of this virus and its possible association with symptoms or acute disease. AgIV-1 could potentially be used to develop biological or molecular tools, such as a viral vector to carry interfering RNA molecules for CBW control.

Simulated Soil Moisture and Planting Material Health on the Behaviour of Cosmopolites sordidus, Germar (Coleoptera: Curculionidae)

The pest status of Cosmopolites sordidus has been related to farm sanitation, environmental conditions and local weevil biotypes. This study was to confirm the inherent fecundity of endemic weevils, soil moisture effect and planting material health status that may contribute to weevil behaviour. Adult banana weevils were confined to plantain rhizomes, which were then subjected to four soil moisture regimens for 65 days. In another experiment to measure potential fecundity, weevils collected from the farmer&amp;rsquo;s field were dissected to determine the internal egg follicles. Planting material with different initial weevil egg infestations on the pseudostem were confined below insect screening net in growing pots. Larva damage and stage populations were determined after 22 weeks. The results showed that weevils confined to plants under moisture stress had higher corm damage than irrigated and vigorously growing plants. A lower number of weevils were associated with plants under moisture stress than vigorously growing plants. The maximum number of mature egg follicles present in the ovaries of female weevils was 17. In general, the mean number of mature egg follicles was 4 per female adult weevil. Infested planting material with initial estimated number of 0.3 eggs per sucker resulted in 2.3 adult emergence and &amp;asymp; 34% corm cross section damage after 154 days. The potential egg follicles albeit slow weevil population build-up reiterates the k-selected nature of the banana weevil. The egg follicles in adult female ovaries were high and comparable with weevils in other banana growing regions. The default health status of planting material was confirmed to be a contributing factor to weevil build-up in confinement. Soil moisture increased weevil survival but the improved plant vigour compensated for weevil damage.

Using the Nematode, Steinernema carpocapsae, to Control Peachtree Borer (Synanthedon exitiosa): Optimization of Application Rates and Secondary Benefits in Control of Root-Feeding Weevils

The peachtree borer, Synanthedon exitiosa (Say) (Lepidoptera: Sesiidae), is a major pest of stone fruits including the peach Prunus persica (L.) Batsch. The entomopathogenic nematode, Steinernema carpocapsae, was previously shown to be an effective tool for controlling S. exitiosa. In orchards where irrigation is not available, a sprayable gel (Barricade®) can be used to maintain soil moisture which can facilitate nematode efficacy. However, rates of nematode and Barricade® application had not been optimized for their maximum economic and biocontrol efficiency. Therefore, our objective was to compare rates of S. carpocapsae and Barricade® in field trials. Nematodes were tested at per-tree application rates of 1.5 million, 1 million and 0.5 million infective juveniles. The sprayable gel was used at two rates, 4% and 2%. A reduction in the used nematodes from 1.5 million to 0.5 million per tree showed no difference in efficacy. Similarly, using the gel at half rate also did not impact the efficacy, and treatments containing nematodes controlled the S. exitiosa better than the chlorpyrifos control in several of the tests (p &lt; 0.05). As an added benefit, the nematode treatments were also able to reduce the prevalence of weevil (Coleoptera: Curculionidae) populations as secondary pests of the peach trees. The lower rates of grower inputs will reduce costs, making the nematode biocontrol of the peachtree borer more likely to be adopted by commercial growers of peach.

Immune Responses of Rhynchophorus ferrugineus to a New Strain of Beauveria bassiana

Evaluating a novel fungal strain’s pathogenicity to important pests and their involved immune responses may give crucial data on a broad scale for future use in pest management strategies. Date palms are mostly destroyed by invading populations of red palm weevils; thus, developing natural biopesticides for them requires a comprehensive screening program of plant secondary metabolites. In this research, we examined the pathogenicity of a new strain of Beauveria bassiana on an important agricultural pest, Rhynchophorus ferrugineus, by measuring the relative activity of defensive enzymes and detoxifying enzymes in certain larval instars. Our findings reveal that the B. bassiana strain may infect the instars of R. ferrugineus, and its pathogenicity to the larvae steadily increases as the spore concentration increases. Seven days after inoculation, the LC50 (the median lethal concentration) of B. bassiana was 490.42 × 105 and 2974.47 × 108 spores/mL for the second and fourth instar R. ferrugineus, respectively, and the LC50 of B. bassiana for each R. ferrugineus instar decreased with infection time, indicating a significant dose effect. Infected R. ferrugineus larvae of the second instars showed considerable changes in the activity of both protecting and detoxifying enzymes (peroxidase, catalase, superoxide dismutase, Cytochrome P450, glutathione S transferase (GST), and esterase) as infection time progressed. In addition, R. ferrugineus larvae that were infected with B. bassiana had enzyme activity that persisted from 24 to 48 h, which was much longer than in the control group. Lethality of B. bassiana resulted in elevated expressions of GST, Esterase, and Cytochrome P450 responsive genes. In conclusion, the results of this research indicate that B. bassiana may be utilized as a bio-insecticide to suppress young larvae of R. ferrugineus in an integrated pest management program.

Susceptibility of Sitophilus zeamais (Coleoptera: Curculionidae) to selected stored product insecticides in the Central region of Ghana

Sitophilus zeamais is a major pest of stored grains in Ghana and its control can be achieved through an Integrated Pest Management approach, which includes the judicious use of effective and selective insecticides. However, persistent use of synthetic protectants can cause insecticide resistance, militating against control. It is therefore important to monitor the effectiveness of these products to justify their continuous use and to detect the emergence of resistance. This study evaluated the efficacy of two commonly used commercial insecticide products namely Agricombi® (30% fenitrothion + 10% fenvalerate) and Betallic Super® (80 g pirimiphos-methyl + 15 g permethrin) on adult S. zeamais populations from three districts in the Central region of Ghana. The median knockdown times (KT 50 s) of the products at their recommended label concentrations (RLCs) were 15.13–53.42 min for Agricombi® and 17.17–63.70 min for Betallic Super® while mortalities after 24 h of insecticide exposure were 52.00–80.00% and 21.33–58.67%, respectively. Concentration-response effect of the composite insecticide products showed median lethal concentrations (LC 50 s) of 8149–12827 mg/L for Agricombi® and 2638–4411 mg/L for Betallic Super®. Comparisons of the RLCs of the products and their respective LC 50 s and LC 95 s indicate decreased susceptibility in the weevil populations. The insecticides were ineffective against the S. zeamais populations at their recommended label concentrations. The decreased susceptibilities pose challenges for effective management of the pest and hence the need for alternative effective management methods or products with different active ingredients in these communities. • Insecticidal activity on adult Sitophilus zeamais in Ghana was assessed. • Agricombi® and Betallic Super® were used for the assays. • At their recommended rates, Agricombi® induced a faster S. zeamais knockdown. • Mortality of adult Sitophilus zeamais was 21.33–80.00%. • S. zeamais from the sampled districts were resistant to the insecticides.

The Effect of Maize Weevil Population Density (Sitophilus zeamais M.) on Maize Weight Loss and The Number of Progeni

The effort of increasing corn production is not only observing the process of the cultivation, but it also needs to observe the handling of post-harvest in order to be able to keep the quality of corn.Post-harvest handling that needs to be considered is when storage. In the storage of corn or other grain can be stored shrinkage of grain weight, this is changed by the presence of fungi, rats and insects. Post-harvest insects that are mostly found in storage are Sitophilus zeamais M. or Maize weevil. The population density of S. zeamais will affect the corn shrinkage, damage, and the number of progeny. This research aims to investigate the effect of S. zeamais population density toward the corn seed damage, shrinkage, the number of progeny, sex ratio, and mortality. This study uses a Completely Randomized Design (CRD) consisting of 5 treatments and repeatition for about 3 times. This treatment consists of pest infestations of 3 pairs, 6 pairs, 9 pairs, 12 pairs and 15 pairs.The result shows that the different population density in every treatment impacts the corn seed damage, weight loss, number of progeny, sex ratio, and the mortality. The population S. zeamaisof 15 pairs in the treatment can cause the damage of seeds for about 50,00%, 39,43% of weight loss, and the amount of progeny for about 171,67 and the mortality for about 33,33%. The population S. zeamaisof 3 pairs in the treatment can cause the damage of seeds for about 20,67%, 11,82% of weight loss, and the amount of progeny for about 56,67 and the mortality for about 16,67%.&#x0D; &#x0D; Keywords :Corn, Population Density, Sitophilus zeamais M., Maize weight loss.

Evaluation of resistance of six chickpea cultivars to the cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchinae) with age-stage, two-sex life table

The cowpea weevil, Callosobruchus maculatus (F.), is an important insect of stored grains with a worldwide distribution. The effect of six chickpea cultivars namely Adel, Azad, Azkan, Hashem, Goksu, and Mansour on the life history, population growth, and reproduction parameters of C. maculatus was investigated in the laboratory at 30 ± 2 oC, 60 ± 5% RH and 12L:12D, using the age-stage, two-sex life table method. The cowpea weevils fed on Azkan, Azad, and Goksu cultivars have a longer total development period, whereas those fed on Adel cultivar, have shorter ones. The longer longevity occurs in the insects fed on Goksu, Azad, and Adel cultivars, respectively, whereas, shorter ones in Hashem cultivar. The cowpea weevil females fed on Azkan and Hashem cultivars have higher and lower fecundity, respectively. The intrinsic rate of natural increase (r) shows a more increase in the cowpea weevil populations in Adel than Azad cultivar. The highest and lowest age-specific fertilities occur in Azkan and Hashem, respectively. The C. maculatus female weight decreases and increases with feeding on the cultivars Azad and Adel, respectively. Based on our findings, Adel is a moderately susceptible and Azad and Hashem are resistant hosts for feeding C. maculatus. So, resistant cultivars may be a safe and clean method for stored crop preservation and storage pest control.

The effect of some different watermelon varieties on Melon Weevil Acythopeus curvirostris persicus population in Sulaimani Governorate

This study was conducted during April–August 2020, in an open field at Qularasi Research Station, Sulaimani, Kurdistan Region-Iraq, to determine the effect of watermelon variety on population density of melon weevil Actopeus curvirostris persicus. Results showed that the melon weevil has distinct daily activities. Two activity peaks were observed in late-June and early-July. The general mean of population density on June 28 was (1.611) weevil /week, which was less than July 4 (2.583) weevils/week, the lowest number of weevils were observed at 7:00 am on the variety (Qamar F1) with (0.789) weevil/hour. Whereas, the highest number of weevil was observed at 7:00 am on Crimson Sweet variety with (1.525) weevil/hour. However, at 11:00 am, all varieties (Charleston Gray, Topgun F1, king Charles, Qamar F1, and Crimson Sweet) recorded the highest number of weevil (4.571, 4.238, 4.048, 4.048 and 1.524) weevil/hour, respectively. The population densities of melon weevil were high on all watermelon varieties in the last week of June and first week of July. Temperature, relative humidity, and wind speed correlations showed a great effect on melon weevil population density during the study period. The correlation was negative significant (-0.208) for temperature in the variety Crimson Sweet, while it was positive significant in the other varieties of Charleston Gray, Topgun F1, and King Charles with (0.165, 0.183 and 0.147), respectively. The correlation was positive significantly for relative humidity in the variety Crimson Sweet) with (0.165) however, it was negative significant for wind speed in the variety Topgun F1 with (0.137).