Effect of mango weevil (Coleoptera: Curculionidae) damage on mango seed viability in Tanzania

Studies were conducted at the horticulture unit of Sokoine University of Agriculture, Morogoro, Tanzania, to assess the incidence and effect of mango weevil, Cryptorhynchus mangiferae (F.) (Coleoptera: Curculionidae), infestation on mango, Mangifera indica L., seed viability. Three polyembryo mango cultivars ('Sindano nyeusi', 'Sindano nyeupe', and 'Dodo') as well as three monoembryo mango cultivars ('Ex-horticulture', 'Tango', and 'Bongwa') were collected and examined for the presence of C. mangiferae. The effect of seed damage on viability was assessed for both naturally and artificially damaged seeds. However, for artificially damaged seeds, the viability was assessed by cutting away 0, 25, 50, or 75% of the cotyledon before planting. In this experiment, only monoembryo mango cultivars were used. All the examined cultivars were infested by C. mangiferae, although at varying levels. Polyembryo mango cultivars were relatively more infested than monoembryo cultivars. Bongwa and Tango were least infested, whereas Sindano nyeusi recorded the highest C. mangiferae incidence. Germination rates of damaged seeds of polyembryonic cultivars differed significantly from the uninfested control, except for Sindano nyeusi. There were no significant differences in germination percentage among the three monoembryo cultivars, and all the cultivars differed significantly from the uninfested control. The germination rates of seeds with 25% of their cotyledons removed did not differ significantly from the undamaged seeds, indicating that monoembryo cultivar seeds can withstand up to 25% damage and germinate successfully.     

Mango seed weevil (Coleoptera: Curculionidae) and premature fruit drop in mangoes

The effect of infestations of mango seed weevil, Sternochetus mangiferae (F.), on premature fruit drop of mangoes was investigated. Mango fruits ('Haden') of equal size were collected both off the ground and from the tree at four times during the season (June-August). If weevil-infested fruit were more prone to dropping than uninfested fruit, the prediction was that a higher infestation rate would be found in fruit on the ground compared with fruit on the tree. Average fruit weight was used as an indicator of fruit maturity. The seed infestation rate was significantly higher in fruit collected off the ground compared with fruit collected from the tree in 38 g and 79 g (early-season) fruit but not significantly different in 207 g (midseason) and 281 g (late season) fruit. The age distribution of weevils and the number of insects in infested fruits were similar for ground and tree fruits on all dates. Results suggest that mango seed weevil infestation can increase fruit drop during early fruit development.     

The mango seed weevil Sternochetus mangiferae (Fabricius) (Coleoptera: Curculionidae) is characterized by low genetic diversity and lack of genetic structure

1. The mango seed weevil Sternochetus mangiferae (Fabricius) is distributed across the major mango-producing areas of the world and causes significant economic losses of mango fruit. Despite its importance as a crop pest, we have only limited information on the population genetics of the mango seed weevil.
2. Here, we examined the genetic diversity of this important pest using specimens intercepted by Beijing Customs District P. R. in China from 41 countries and regions. We used segments of the mitochondrial gene cytochrome c oxidase subunit I and the nuclear gene elongation factor 1-alpha to examine population genetic structure in this species.
3. Our results showed that genetic diversity is low in S. mangiferae, with a mean genetic distance of 0.095–0.14%. Other population genetic parameters also indicated a low level of genetic diversity among samples from a large geographic range. Analysis of molecular variance revealed little population genetic structure, and mismatch distribution analyses provided evidence of a population expansion, although other demographic metrics of population expansion were nonsignificant.
4. We suggest that the observed low level of genetic diversity and population genetic structure in S. mangiferae supports the hypothesis that the population genetics of this species has been impacted by anthropogenic transportation of mangoes and weevils.

     

Impact of azadirachtin on vine weevil (Coleoptera: Curculionidae) reproduction

Abstract 1 The dose–response of azadirachtin on vine weevil, Otiorhynchus sulcatus (Fabricius), reproduction is investigated by confining adults to feed on treated Taxus × media leaves, and by counting and evaluating development in the resulting eggs. 2 A dosage‐dependent reduction in oviposition is discovered for foliar surface residues of azadirachtin, with an EC₅₀ of 25–50 parts per million (p.p.m) and 99.2% inhibition of viable egg production with 100 p.p.m. 3 Switching weevils from treated to untreated foliage allows reproductive capability to be restored for weevils that cease egg laying after azadirachtin exposure of 50 p.p.m. Weevils that had already started laying eggs in untreated groups soon cease oviposition once switched to azadirachtin‐treated foliage. 4 A transovarial effect results in a decrease in the percentage of viable eggs as the azadirachtin concentration increases. 5 The amount of feeding on foliage does not appreciably decrease at these hormonally effective concentrations, and adult weevil mortality is only slightly greater in the azadirachtin‐treated groups. Therefore, the overall effect of azadirachtin on weevil populations in the field is difficult to assess, except by collecting weevils to determine whether they are able to lay viable eggs.     

Delimiting baridine weevil evolution (Coleoptera: Curculionidae: Baridinae)

Since the erection of the weevil subfamily Baridinae by Schönherr in 1836, no phylogenetic hypothesis using cladistic methods has been proposed for this extraordinarily diverse group. This study provides the first hypothesis for the evolution of Baridinae using phylogenetic methods, including 301 taxa and 113 morphological characters. Despite fairly well‐resolved results, indicating paraphyly of nearly all of the currently recognized intrasubfamilial divisions, no change to the current classification is made. Even though groupings are proposed based on the final results, it is believed that more rigorous analyses need to be made prior to a re‐evaluation and subsequent alteration of the current classification. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010.     

Effect of irradiation on mating ability in the male sweetpotato weevil (Coleoptera: Curculionidae)

The sterile insect technique (SIT) is widely used for suppressing or eradicating target pest insect populations. The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females. Irradiation is the effective manner to sterilize mass-reared insects. The negative impacts of this procedure are not limited to damage on reproductive cells. Gamma-radiation damages the epithelial tissue of midgut, which affects the alimentation in insects. Irradiated males alter their mating behavior over time because of the depression of metabolic activity by sterilization. In this study, we evaluated the male mating performance and sexually compatibility of irradiated male Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae) with a 200-Gy dose, as currently used in the SIT program in Okinawa Prefecture, throughout 16 d after irradiation in the laboratory. The mating ability of irradiated males did not differ from that of control males for about a week. However, the mating ability of irradiated male drastically decreased thereafter. We consider that irradiated male C. formicarius elegantulus with a 200-Gy dose had no major effect on male mating behavior approximately for a week after irradiation.     

Boll weevil (Coleoptera: Curculionidae) damage to cotton bolls under standard and proactive spraying

In some parts of the boll weevil's, Anthonomus grandis grandis (Boheman) (Coleoptera: Curculionidae), distribution from the United States to Argentina, insecticides are applied after cut-out (end of square production) when bolls are the predominant stage of fruiting body. This study demonstrates that the standard spray regime in southern Texas, which involves insecticide applications after cut-out, did not result in more bolls than a nonsprayed control. An alternative "proactive" spray regime focusing on protecting large squares before cut-out resulted in 1.9- to 2.5-fold more bolls in the lower half of the canopies than the control. At one of two experimental field locations, the percentage of damaged boll carpels was 3-fold greater in the standard spray regime's lower canopy than in the proactive spray regime, and the percentage in the control was 1.6-fold greater than in the standard regime. At both experimental field locations, the upper canopy control had 2.1- to 2.3-fold greater percentages of carpel damage than the proactive spray regime. The standard spray regime resulted in 2.3-fold greater percentage of carpel damage than the proactive regime. In the control and the standard spray regime, percentages of upper canopy nondamaged bolls were mostly lower than or not different from percentages of bolls with one, two, three, or all four carpels damaged, but in the proactive regime, percentage of nondamaged bolls in the upper canopy was greater than percentages of bolls with one or more damaged carpels. Reasons for the ineffectiveness of the standard spray regime and the benefits observed in the proactive approach are discussed.     

Karyological investigations on seven weevil species (Coleoptera, Curculionidae)

Karyological studies were carried out on seven Palaearctic weevils. The following chromosome numbers were found in individual species, i.e. Otiorhynchus niger (F.), Phyllobius viridearis (Laich.), Phyllobius scutellaris Redt., Phyllobius calcaratus (F.), Polydrusus cervinus (L.), and Brachyderes incanus (L.) 2n = 22, n Male = 10 + Xyp, in Lixus elegantulus (Boh.) 2n = 22, n Male = 21 + Xyp. The heterochromosomes of all the examined species form, in the first meiotic metaphase, a typical parachute bivalent.     

Boll weevil (Coleoptera: Curculionidae) survival through the seed cotton cleaning process in the cotton gin

There is concern that gins located in boll weevil, Anthonomus grandis grandis Boheman, eradication zones may become points of reintroduction when they process cotton grown in a neighboring infested area. We estimated boll weevil survival through two typical machine sequences used in commercial cotton gins to clean and dry the seed cotton in advance of the gin stand, as well as separately through two incline cylinder cleaners or one or two tower dryers operating at different temperatures. Large numbers of laboratory-reared adult boll weevils were marked with fluorescent powder, fed into the test system, and recovered with the assistance of blacklights. We found no evidence of survival through the seed cotton cleaning systems even when the dryers were not heated, or when passed separately through the two incline cleaners alone. Upper confidence limits (95%) were calculated for the observed zero recoveries based on sample size and the binomial distribution, and these represent the statistical worst-case (i.e., highest) survival potential. Survival through heated tower dryers declined rapidly to zero at higher temperatures, especially when two dryers were running. Although we conclude that the potential for survival of weevils in the seed cotton to the gin stand is zero or close to zero, a small percentage of live weevils was recovered in the green boll/rock trap, which may represent the greatest threat of reintroduction at the gin. Escape of live weevils with the gin trash is also possible, and studies addressing this issue will be presented elsewhere.     

Speciation in the sub-Antarctic weevil genus Dusmoecetes Jeannel (Coleoptera: Curculionidae)

Relatively few instances of sympatric speciation have been reported in the literature, and both theoretical and empirical studies of this mode of speciation remain controversial. Recently, a model of sympatric speciation less restrictive than earlier ones has been proposed. This study presents a hypothetical speciation scenario, based on current observations, which seems to be consistent with the new model. Two morphologically similar, though ecologically separated, species are identified in the Dusmoecetes similis (C. O. Waterhouse) species complex on Marion Island (46° 54'S, 37° 45'E), based on a study of the morphology, biology and ecology of the group. Differences between the demands placed on angiosperm- and bryophyte-feeding members of the complex, and the differing demands of bryophyte and angiosperm-dominated communities, coupled with low vagility and a high degree of assortative mating, suggest that a sympatric model can be used to explain speciation in this genus, which probably occurred within the last 10,000 years. Differences between Dusmoecetes marioni Jeannel and D. Similis (Waterhouse) are discussed, and a lectotype designated for the latter species.     

Compensatory response of cranberry to simulated damage by cranberry weevil (Anthonomus musculus Say) (Coleoptera: Curculionidae)

Cranberry weevil (Anthonomus musculus Say), a key pest of cranberry (Vaccinium macrocarpon Aiton) in Massachusetts, deposits eggs in unopened flowers and often severs the flower pedicel from the peduncle. The compensatory response of cranberry to simulated cranberry weevil damage was investigated by severing the pedicel of unopened flowers with scissors. When intensity of damage was varied on the cultivar Early Black, complete compensation was observed at three of four sites after removal of 33% of a peduncle's unopened flowers, but a approximately 37% decline in number of fruit and weight of berries per peduncle was observed when 67% of unopened flowers were removed. When timing of damage was varied at sites planted to the cultivar Howes, no differences were observed when 50% of unopened flowers were clipped from a peduncle early versus late in preblossom peduncle growth. However, both the early and late clipping treatments resulted in a 30% decrease in the number and weight of berries per peduncle when compared with the no clipping treatment. These results suggest that cranberry has the ability to tolerate low to moderate levels of weevil damage, but a substantial data base will be required to determine any appropriate changes in threshold recommendations.     

Size-dependent feeding and reproduction by boll weevil (Coleoptera: Curculionidae)

The considerable variation in adult size of the boll weevil, Anthonomus grandis grandis Boheman, has been well documented, but the influences of adult size on reproductive rate are not known. We examined the relationship between the size of boll weevils and their feeding and oviposition. Weevils weighed to the nearest milligram were grouped into five categories based on pupal weight: < or =5, 6-10, 11-15, 16-20, and >20 mg. Numbers of lifetime punctures produced in flower buds (squares) of cotton, Gossypium hirsutum L., by both sexes of adults tended to increase with pupal weight. Boll weevil females with pupal weights >10 mg produced progeny with significantly higher survival to adulthood and also produced a higher percentage of female progeny than those with pupal weights < or =10 mg. The population growth indices for females having pupal weights >10 mg averaged 1.8-fold higher than those of females weighing < or =10 mg. Survivorship of adults of both sexes also tended to increase with pupal weight. The percentage of females laying eggs on any given day averaged 2.1 times higher when their pupal weights were >10 mg than when their pupal weights were < or =10 mg. Although small size negatively affected female reproductive potential, even extremely small females produced some viable offspring. However, the penalties of small adult size, in terms of longevity and reproductive potential, suggest that cultural practices that result in the production of small adults may be used to impact weevil populations.     

Karyotypic characterization of three weevil species (Coleoptera: Curculionidae, Brachyderini)

Karyotypes of three species, Brachyderes incanus, Brachysomus setiger and Paophilus afflatus, belonging to the tribe Brachyderini, were studied using C-banding technique. The species share the same chromosome number 2n = 22 and meioformula n = 10+Xy(p) at all metaphase 1 plates of spermatid division. Some differences between karyotypes were observed in terms of centromere positions and C-band sizes. Most chromosomes are meta- or submetacentric and form a graded series in respect to length. The chromosomes resemble one another in having a rather small amount of heterochromatin restricted to the pericentromeric region and visible as dark stained blocks mainly during early stages of nuclear division. Only in Brachyderes incanus do larger bands occur at mitotic metaphase and diakinesis. These cytogenetic data are in agreement with karyological findings obtained in other species of Brachyderini so far examined.     

Strategies of emergence in the chestnut weevil Curculio elephas (Coleoptera: Curculionidae)

In the chestnut weevil Curculio elephas, adult emergences spread over 3 or 4 years due to prolonged larval diapause in some individuals. Weevils with an extended diapause emerge, on the average, 1–10 days before those with simple diapause, but whatever the age of insects, emergences occur always from mid-August to early October. When the summer is dry, some adults cannot emerge because of the hardness of the soil. Emergence sucess of adults is smaller in females than in males. The result is that the sex ratio is female-biased before emergence and male-biased after. Summer drought cannot be predicted by the chestnut weevil, and when the soil is dry 27–78% of females cannot emerge and do not reproduce. The year after a summer drought, many reproducing females may emerge from larvae with prolonged diapause. These results suggest an evolutionary influence on the variability in diapause duration. Computer simulations and observations do not support the hypothesis that the main cause of variation in diapause length is the existence of several distinct genotypes within populations. On the contrary, our data strengthen the hypothesis for coin-flipping plasticity discussed in a previous paper.     

Strain distribution of alfalfa weevil (Coleoptera: Curculionidae) in an intergrade zone

Strain distribution for the alfalfa weevil, Hypera postica (Gyllenhal), was determined for the five major alfalfa-growing regions of New Mexico. Mitochondrial DNA from field-collected weevils at each location was digested and sequenced to differentiate among strains. Eastern, Egyptian, and western strains were recovered, along with a population not matching any known strain. The majority of sites examined had populations of two strains intermingled within a field. This is the first confirmation of the presence of all three strains within the same geographic region. Possible implications for alfalfa weevil management are discussed.     

Temperature-dependent development and reproduction of the boll weevil (Coleoptera: Curculionidae)

Abstract Effects of temperature on development, survival, and fecundity of boll weevil, Anthonomus grandis grandis Boheman, were assessed at 10, 11, 12, 15,20,25,30,35,45, and 46 °C; 65% relative humidity; and a photoperiod of 13:11 (L: D) h. The mortality of boll weevil immature stages was 100% at 12°C and decreased to 36.4% as the temperature increased to 25°C. When the temperature increased from 30 °C to 45 °C, the mortality of weevils also increased from 50.1% to 100%. From 15°C to 35°C, the bollweevilpreimaginal development rate was linearly related to temperature. The average development time of total boll weevil immature lifestages decreased 3.6-fold and the preovipositional period decreased 3.3-fold when the temperature was increased from 15°C to 30°C. The lower threshold for development was estimated at 10.9, 6.6, 7.0, and 9.0 °C for eggs, larval, pupal, and total immature stages, respectively, with total thermal time requirement to complete immature stages of 281.8 DD (degree day) (15°C) and 247.8 DD (35 °C). At 1LC and 46°C, weevil females did not oviposit. Longevity of adult females decreased 4.6-fold with increasing temperatures from 15°C to 35°C. Fecundity increased with increasing temperatures up to 30°C and significantly decreased thereafter. These findings will be useful in creating a temperature-based degree-day model for predicting the occurrence of key life stages in the field. An accurate predictor of a pest's development can be very important in determining sampling protocols, timing insecticide applications, or implementing an integrated pest management control strategy targeting susceptible life stages.     

Distribution of alfalfa weevil (Coleoptera: Curculionidae) larvae among postcutting locations

A field study was conducted in 1996 and 1997 to determine survival and spatial patterns of alfalfa weevil, Hypera postica (Gyllenhal), larvae within and between windrows of swathed alfalfa, Medicago sativa L., forage as dry matter concentration increased. After harvest, the percentage of live weevil larvae residing in swathed forage decreased as swath dry matter percentage increased. Conversely, larval populations in stubble between windrows increased with increasing swath dry matter. Larval populations in stubble under windrowed forage increased slightly as windrowed forage dry matter increased. Applications of these results for the development of alfalfa harvest systems for improved cultural control of alfalfa weevil are discussed.     

Sexual dimorphism of guava weevil Conotrachelus psidii Marshall (Coleoptera: Curculionidae)

We investigate structural and behavioral differences between male and female adults of guava weevil, Conotrachelus psidii Marshall, 1922 to help in sex determination. Weevils collected from a commercial guava orchard were individually caged and maintained under laboratory conditions. Every day ten individuals were grouped and their behavior was observed. During mating the males and females were identified. Fifty weevils of each sex were killed and they were observed with stereoscopic microscope. The antenna insertion on the rostrum and hair on the thorax and abdomen surfaces were examined. Length and width of body, pronotum, last abdominal sternite and rostrum were also taken. Behaviorally, the male weevils produce audible sound by stridulation of abdomen while females do not. In the females, the body and pronotum width and body a rostrum length were higher than in the males, but the last abdominal sternite was smaller. Three other structural differences were visible with the naked eye: 1) the anterior region of pronotum have scarce hair or have not in the females and hair is dense in the males; 2) the last tergite of females is hidden by the penultimate tergite whereas in the males is visible; 3) the first abdominal sternite of females is more prominent, very convex and without or with little bristle. In the males it is slightly concave and with abundant hair. The male-female differences found in this work allow, without hurt or change insect behavior, an efficient sex determination of guava weevil.     

Boll weevil (Coleoptera: Curculionidae) survival through cotton gin trash fans

There is concern that cotton gins may serve as loci for reintroduction of boll weevils, Anthonomus grandis grandis Boheman, to eradicated or suppressed zones when processing weevil-infested cotton from neighboring zones. Previous work has shown that virtually all weevils entering the gin in the seed cotton will be removed before they reach the gin stand. Those not killed by the seed cotton cleaning machinery will be shunted alive into the trash fraction, which passes through a centrifugal trash fan before exiting the gin. The objective of this study was to determine survival potential of boll weevils passed through a trash fan. Marked adult weevils were distributed in gin trash and fed through a 82.6-cm (32.5-in.) diameter centrifugal fan operated across a range of fan-tip speeds. A small number of boll weevils were recovered alive immediately after passage through the fan, but all were severely injured and did not survive 24 h. In another experiment, green bolls infested with both adult- and larval-stage weevils were fed through the fan. Several teneral adults survived 24 h, and there was no evidence that fan-tip speed affected either initial survival of weevils, or the number of unbroken boll locks that could harbor an infesting weevil. Thus, designating a minimum fan-tip speed for ensuring complete kill is not possible for the boll weevil. Experiments suggest that a device installed in a gin that partially crushes or cracks bolls open before entering a trash fan will increase mortality, possibly enough that further precautions would be unnecessary.