Adult Alfalfa Weevils Research Articles

Overwintering Survival of the Adult Alfalfa Weevil 1 , 2

Acclimated adult alfalfa weevils, in envelope cages, were placed in alfalfa fields and along their borders near Ithaca during early December. Subsequently cages were collected at 3-wk intervals through March. Total overwintering survival in all sites was 25%. There was no consistent difference in survival between sites or fields. The rate of survival was not constant through the winter period, but decreased markedly in late January and February.

Positive Phototaxis of Adult Alfalfa Weevils1 to Visible and near-Infrared Radiation

The action spectrum of positive phototaxis in adult alfalfa weevils, Hypera postica (Gyllenhal), was evaluated by placing groups of 50 starved weevils in a closed cylindrical orientation chamber illuminated at one end by a Bausch and Lomb monochromator. Weevils responded well to green light (500–550 nm), but they were most strongly attracted to wavelengths in the far red and near infrared region. The response to red light was almost completely eliminated when the vertex of each weevil's head capsule was covered with an opaque lacquer. Weevils with clear shellac over the top of the head capsule had the same bimodal response to colored light as unpainted weevils, so illumination of the head must either stimulate an extra-ocular photoreceptor or else somehow change the sensitivity of the compound eyes. Three structures which lie just below the cephalic exoskeleton have been identified as possible photoreceptors: the brain, a pair of tegumentary nerves, and an elongate pit at the top of the frons which could mark the site of an internal ocellus.

Effective Range and Species Specificity of Host Recognition in Adult Alfalfa Weevils, Hypera postica1

A behavioral bioassay was used to determine the maximum range over which visual cues attract aflfalfa weevils, Hypera postica (Gyllenhal), to their principle host plant. The range proved to be dependent on the amount of alfalfa used, but in general, a weevil's response did not decline significantly until the alfalfa subtended an angle less than 120° in its visual field. The visual response was also shown to be only moderately host specific; weevils could distinguish alfalfa from periwinkle and Douglas fir branchlets, but could not discriminate between alfalfa and red clover, oats, bluegrass, or beans.

Dispersal Following Establishment in Michigan of Microctonus aethiops , 1 a Parasitoid of Adult Alfalfa Weevils 23

Microctonus aethiops (Nees), a European braconid parasitoid of adult alfalfa weevils, Hypera postica (Gyllenhall), was first established in the eastern United States in 1961 (Coles and Puttler 1963). Brunson and Coles (1968) listed release localities of M. aethiops through 1967, and it has been released in many other localities in the East and Midwest since then. Day et al. (1971) described the distribution of M. aethiops in the eastern United States and gave the dates of first recovery in many eastern states. However, to my knowledge it is not known how far M. aethiops has dispersed from an initial release site where a known number of parasitoids was released.

“Indirect-Choice” Olfactometer Experiments on Adult Alfalfa Weevils, 2

The 1st experimental evidence that adult alfalfa weevils, Hypera postica (Gyllenhal), are attracted by the odor of their principal host plant, Medicago sativa, was published in 1966 by Byrne and Steinhauer. They used a specially designed “indirect-choice” olfactometer to test attractiveness of fresh alfalfa over short distances (less than 10 cm), and concluded, in part, that “alfalfa produces a volatile substance which elicits an olfactory response from the alfalfa weevil.” Subsequently, however, this research has been extrapolated into an olfactory orientation hypothesis which proposes that adult weevils are able to locate suitable host plants by tracking the odor of alfalfa to its source (Hsiao 1969). This hypothesis has developed informally, largely without the benefit of experimental verification, and exists despite observational evidence which challenges its basic assumptions.

Kinetic Orientation Experiments on Adult Alfalfa Weevils1

Observed behavior of adult alfalfa weevils, Hypera postica (Gyllenhal), seems to be inconsistent with the hypothesis that weevils rely primarily upon olfactory cues to locate their principle host plant, Mcdicago sativa (Meyer and Raffensperger, 1974). In light of this disparity, the existing experimental data which support an olfactory orientation hypothesis were carefully reexamined.

MICROCTONUS STELLERI (HYMENOPTERA: BRACONIDAE, EUPHORINAE), A NEW PARASITE OF THE ALFALFA WEEVIL INTRODUCED INTO THE UNITED STATES

AbstractMicroctonus stelleri Loan is described as a new species. This euphorine braconid occurs in France, Germany, Sweden, and Russia. It is umvoltine and its only known host is the alfalfa weevil, Hypera postica (Gyllenhal). In the spring the mature parasite larva issues from the overwintered adult host and forms a white cocoon in the ground litter. In about 2 weeks the adult parasite emerges, mates, and oviposits in larva of the alfalfa weevil. The parasite egg hatches and the first-instar larva remains within the host until the following spring. In northern France M. stelleri was the dominant parasite in overwintering adults of H. postica. Parasitism ranged from 0 to 13% though it was usually less than 6%. Laboratory studies showed that M. stelleri females live longer, have a higher rate of oviposition, and parasitize more hosts than females of M. colesi Drea, a parasite of the weevil in the United Slates. A technique is described for the recovery of M. stelleri from adult alfalfa weevils. From 1966 to 1970, 4387 parasites were imported from France and released at 24 localities in the United States.

Activity of the Alfalfa Weevil 1 and its Parasites in North Georgia 2

Adult alfalfa weevils, Hypera postica (Gyllenhal), were collected with phototaxis traps from February 2 to ApriL 26, 1971, in Clarke and Fulton Counties, Georgia. Of 193 female weevils collected, 183 contained developed ovaries. Dissection revealed parasitism by Hyalomyodes triangulifer (Loew) (Tachinidae). Bathyplectes curculionis (Thomson) (Ichneumonidae) was reared from larvae consistently. LarvaL parasitism reached high levels in late May in the 2 regularly surveyed fields. One periodically sampled field had 97.5% parasitism in early May. After April 15, 90% or more of the B. curculionis entered diapause. The value of continuing investigations of parasitism of the alfalfa weevil and colonization of additional parasitoid species is stressed.

Establishment of Microctonus aethiops, a Parasite of Adult Alfalfa Weevils, in Michigan123

Establishment of Microctonus aethiops, a Parasite of Adult Alfalfa Weevils, in Michigan123

A Net for the Mass Collection of Alfalfa Weevils1

A program requiring the collection of large numbers of adult alfalfa weevils, Hypera postica (Gyllenhal), necessitated the development of an effective collection apparatus. A “trawl net” was designed and constructed to be dragged behind a field motorcycle (Fig. 1). The rectangular outer rim of the net consisted of ½-in.-diam steel rod, 5 ft long and 1 ft high. The net itself consisted of 4 pieces of “tuff-tarp” (vinylized nylon) sewn together. The 2 pieces which made up the top and the bottom were triangular with a base and height of 5 ft. The 2 side pieces were 66 in. long and tapered from a 1 ft width at the base to 6 in. at the point of the net. Lightweight chain was used to attach the net to the rear of the motorcycle.

Susceptibility of Adult Alfalfa Weevils of Low Lipid Content to Selected Insecticides12

Dosage mortality was determined for over wintering field-collected adult Hypera postica (Gyllenhal), and for laboratory-reared newly emerged adults at 3, 7, and 14 days of age using the insecticides carbofuran, methyl parathion, malathion, methoxychlor, and a 1:1 malathion + methoxychlor mixture. Carbofuran was the most effective material, followed in descending order of effectiveness by methyl parathion, malathion, malathion + methoxychlor, and methoxychlor. The amount of methyl parathion and methoxychlor required to kill 50% of the newly emerged adults was greater than that required to give a comparable kill of the over wintered stock. Lipid content of over wintered adults was 8.9% of the dry weight, while that of newly emerged weevils was 7.2% at 3 days, 11.5% at 7 days, and 13.7% at 14 days after emergence. An increase in lipid content had little effect upon any treatment other than methoxychlor. The methoxychlor dosage required for a 50% kill varied from 4.45 µg/weevil at 7.2% lipid content to 41.0 µg/weevil at 13.7%. No added effectiveness was noted from the addition of methoxychlor in the malathion + methoxychlor mixture.

Hibernation and Estivation Habits of the Alfalfa Weevil in West Virginia12

Field experiments to determine some of the hibernation and estivation habits of Hypera postica (Gyllenhal) in West Virginia were begun in December 1965. Soil samplings of caged and uncaged areas of alfalfa were used to ascertain the location and duration of hibernation and estivation sites. Adult weevils were found hibernating in the soil from late December to early March. They gradually emerged from the soil into the fields during mid-March through April, and they estivated in the soil from late June through September. Adult alfalfa weevils were found principally in the top 0.8 inches of the soil.

Sexual Dimorphism and Morphonietric Differences in the Eastern, Western, and Egyptian Alfalfa Weevils1,2

The shape of the last abdominal tergite and sternite was the best diagnostic character for determining the sex of adult alfalfa weevils, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), from both the eastern and western United States, and the Egyptian alfalfa weevil, H. bruneipennis (Boheman). Differences were observed also between the sexes of the eastern alfalfa weevil with regard to the elytral stripe, body size and proportions, position in which the front legs are held at rest, and manner of movement. Body size and proportions also differed significantly between the sexes in the western and Egyptian alfalfa weevils. Body proportions without regard to sex differed significantly among the 3 groups with proportions in the Egyptian alfalfa weevil intermediate between the eastern and western alfalfa weevils.

Leaf Disk Method of Testing Alfalfa Plants for Resistance to Feeding by Adult Alfalfa Weevils1

Several methods of testing adult alfalfa weevils, Hypera postica (Gyllenhal), feeding on detached leaves were evaluated under forced conditions. Dry-weight comparisons of damaged and undamaged pairs of lateral leaflets were time consuming and imprecise. Evaluations comparing leaf areas eaten from leaf disks were rapid, but were influenced by leaf thickness. Leaf area, eaten from leaf disks and then adjusted according to dry weight of the sample, was the most critical measurement of feeding. Adult feeding was influenced by light and by moisture levels used during testing of excised leaf disks. Weevils ate more when tested under constant light than under constant darkness. However, feeding was more erratic in light. Test conditions of constant darkness and uniform moisture levels were recommended. Effects of adult size, sex, and age on feeding were studied. Adult feeding was in direct proportion to body size. Differences in feeding rate (mg leaf material eaten per mg body weight) between large and small weevils as well as between male and female weevils were insignificant. However, because differences in body size exist in most weevil populations, the use of sized adults in feeding tests was recommended. Studies on feeding behavior of nondiapausing adults ranging from 1 to 49 days old showed that freshly emerged adults ate 5-6 times more leaf material than did 4- to 5-week-old adults. Information obtained was used to develop a rapid procedure for classifying alfalfa plants for differential feeding by adult weevils. Data obtained from using the leaf disk test on surviving seedlings from adult feeding preference test are presented.

Aestivation (Summer Diapause) in Hypera postica (Coleoptera: Curculionidae). II. Morphological and Histological Studies of the Alimentary Canal1

The alimentary canal of the adult alfalfa weevil, Hypera postica (Gyllenhal), was studied over a 12-month period. Structures that make up the stomodaeum, ventriculus, and proctodaeum are similar to those of other Curculionidae. The proventriculus consists of 8 sclerotized plates; the ventriculus is anteriorally bulbous, with a tubular posterior half; and the proctodaeum has a cryptonephridial attachment for the 6 Malphighian tubes anterior to the rectum. During aestivation a reduction is noticeable in total gut dimensions and in the cytoplasm of all epithelia and musculature, reflecting a decline of ingestion during adult diapause.

Factors Affecting Resistance of Alfalfa Clones to Adult Feeding and Oviposition of the Alfalfa Weevil in the Laboratory1

Factors affecting the resistance of 25 alfalfa clones to oviposition and feeding of adult alfalfa weevils, Hypera postica (Gyllenhal), were evaluated in the laboratory. Significant differences were found among clones for feeding and oviposition. The 2 responses were interrelated, and both were significantly related to stem diameter and to larval damage observed in the field. Although the clones differed in stem hardness, this fact did not influence fluence oviposition, nor did variations in stem age have any effect on oviposition.

The Attraction of the Alfalfa Weevil, Hypera postica (Coleoptera: Curculionidae), to Alfalfa1

Adult alfalfa weevils, Hypera postica (Gyllenhal), showed a strong olfactory attractancy to fresh alfalfa plant material in an olfactometer, but dried material did not attract them. Responses were strongest when materials were positioned above the insects. Age of the adults and pretest holding period in the refrigerator appeared not to affect the olfactory response; a 2-day pretest starving period elicited a higher response than did any other starving period tested. Fresh alfalfa plant material was extracted with steam distillation, ether extraction, and fractional distillation, and was watered down to dilutions of 0.1%, 0.05%, 0.025%, and 0.0125% by volume. Of these dilutions, that at 0.025% elicited a miximum response, but this response declined markedly when the insects were offered water before they were exposed to the extract. Addition of a 2% sugar solution to the 0.025% extract dilution elicited a higher overall response from the weevils than did any other test substance, including even alfalfa. Weevils with both antennae removed did not respond predictably when exposed to alfalfa vapors in the olfactometer. This phenomenon was thought to result from loss of both geotactic and chemotactic centers of the antennae.

Aestivation (Summer Diapause) in Hypera postica (Coleoptera: Curculionidae). I. Effect of Aestivation, Photoperiods, and Diet on Total Fatty Acids1

Total fatty acids of the adult alfalfa weevil, Hypera postica (Gyllenhal), collected in South Carolina were examined by gas chromatography. Seven acids accounted for approximately 98% of the total: myristic (14:0), palmitic (18:0), palmitoleic (16:1), stearic (18:0), oleic (18:1), linoleic (18:2) and linolenic (18:3). Based on analyses of pre- and postaestivating populations, the 3 principal characteristics noted during this period of reduced metabolism were a decrease in oleic acid, a decrease in monounsaturates, and an increase in polyunsaturates. Little evidence of any larval photoperiodic influence (8 or 16 hours) upon the new adult's fatty-acid composition was observed. However, weevils clearly mirrored the fatty-acid composition of the food source—artificial diet with high linoleic and fresh alfalfa with high linolenic acid.

Respiratory and compositional study on the aestivating insect, Hypera postica (Gyll.) (Curculionidae)

Studies of the adult alfalfa weevil, Hypera postica (Gyll.), in South Carolina have shown that the insect experiences periods of inactivity during midsummer and midwinter. The body composition and respiration of the developmental and adult stages have been studied to determine if any physiological distinctions might exist to characterize better these two periods. Aestivation, occurring during the summer months, clearly demonstrates the typical diapause alteration: low respiration, low water, and high fat. The insect, on the contrary, exhibits none of these characteristics during the winter. The hypothesis is thus presented that the alfalfa weevil in South Carolina aestivates but does not hibernate. The mechanism by which a certain percentage of the population can withstand the winter environment is not known. The insect's developmental periods exhibit compositional and respiratory changes not unlike the normal patterns.

Development of Heptachlor Resistance in the Alfalfa Weevil in Virginia

Because of a general failure of heptachlor treatments to control the alfalfa weevil, Hypera postica (Gyllenhal), in eastern Virginia, laboratory tests were conducted to determine if heptachlor resistance had developed in this pest. Larvae, pupae, and/or adult alfalfa weevils were collected from several counties in Virginia. They were maintained in the insectary until they were 30-day old adults. Individual adults were treated topically with measured drops of heptachlor, or dieldrin, solutions in acetone. The resulting dosage-mortality data indicate that weevils from several counties east of the Allegheny Mountains are resistant to heptachlor, with considerable cross resistance to dieldrin. There was no evidence that weevil from the higher elevations of Virginia had developed heptachlor resistance.