Larvae Of Hypera Postica Research Articles

Bacillus thuringiensis Protein Cry6B (BGSC ID 4D8) is Toxic to Larvae of Hypera postica

Insecticidal proteins produced by strains of Bacillus thuringenesis are specific toward target pests. One of the Bt proteins, Cry 1Ac has been used successfully for controlling crop predation by polyphagous pests Helicoverpa armigera. Structurally, Bt proteins consist of three domains; domain I and III are fairly homologous in various Bt proteins while domain II is hypervariable. The hypervariable domain II is believed to be responsible for specificity toward target pest. Successful deployment of Bt proteins requires knowledge of its specificity toward the insect. Various Bt proteins have been characterized for activity against coleopteran pests. Some Bt proteins of class Cry6 have been found to be active against potato weevil. We have evaluated the activity of Cry6B protein (BGSC-4D8) against lucerne weevil, Hypera postica, which is a major pest of forage crop Medicago sativa. Results revealed that the purified Cry6B protein is significantly active against the coleopteran pest with LC₅₀ value 280 ng/μl. The leaves coated with the purified Cry6 toxin were three times less damaged as compared with the negative control.

Role of Cold Tolerance in the Seasonal Life History ofBathyplectes curculionis(Hymenoptera: Ichneumonidae) in the Southern Great Plains

Emergence patterns and cold tolerance of adult Bathyplectes curculionis (Thomson) were studied in relation to weather conditions that are typical during fall and winter in the Southern Great Plains. Laboratory studies were conducted to confirm that daylength and environmental temperatures prevailing during fall and winter are conducive to termination of diapause, pupal development, and emergence of B. curculionis adults. Mean Julian dates for first detection of the parasite in larvae of Hypera postica (Gyllenhal) were 69 and 72 for two field research sites in Oklahoma. These dates indicate that adults of B. curculionis emerge during winter and are frequently subjected to freezing temperatures as they begin parasitizing the first larvae of H. postica to infest alfalfa, Medicago sativa L., each year. Both laboratory and field studies demonstrate that >80% of adult parasites can survive repeated exposures to daily low temperatures ranging from 0 to −9°C. This level of cold tolerance indicates that the adults can survive during February and March when mean low temperatures are −1 and 3°C, respectively, in central Oklahoma. Although some adults of B. curculionis do emerge during fall and winter in the Southern Great Plains when there are no hosts available, this potential disadvantage to effective biological control is offset somewhat by the cold tolerance of adults, which allows survival during late winter and spring when they parasitize the first larvae of H. postica to infest alfalfa annually.

Probabilities for Encapsulation of Eggs of Bathyplectes curculionis (Hymenoptera: Ichneumonidae) by Larvae of Hypera postica (Coleoptera: Curculionidae) and Resulting Reduction in Effective Parasitism

Encapsulation of eggs of the parasite, Bathyplectes curculionis (Thomson), in larvae of Hypera postica (Gyllenhal) was studied at two locations in Oklahoma from 1976 to 1984. Larvae were dissected to determine total numbers that contained parasites (actual parasitism) and numbers that had at least one unencapsulated parasite (effective parasitism). These data were used to calculate probabilities of one or more parasites being encapsulated by host larvae. Probabilities for encapsulation of one parasite egg ranged from 0.20 to 0.45 depending upon numbers of parasites within a host larva. Probabilities for encapsulation of supernumerary parasites ranged from 0.04 to 0.18. The linear regression of numbers of effectively parasitized larvae per 0.1 m2 on numbers actually parasitized per 0.1 m2 has a slope of 0.77 with an r 2 value of 0.97.

Reduction in Yield and Quality of Leaf and Stem Components of Alfalfa Forage Due to Damage by Larvae of Hypera postica (Coleoptera: Curculionidae)

Variable rates of carbofuran were used to obtain a gradation of larva population densities of the alfalfa weevil, Hypera postica (Gyllenhal), in nonirrigated ‘Oklahoma Common’ alfalfa, Medicago sativa L. Damaged and undamaged alfalfa stems were collected according to a 10-point defoliation rating scale. Leaf and stem components were separated and analyzed for yield and crude protein content. Regression analyses were conducted to correlate alfalfa performance parameters with levels of weevil damage. As damage due to weevil larvae increased, yield reductions in both leaf and stem components were readily apparent. Crude protein content of leaves was reduced as a result of larva feeding. Protein levels in stems were highest early in vegetative growth and declined thereafter. No consistent trends in crude protein content of total herbage could be demonstrated due to high protein levels in stems throughout vegetative growth which masked effects of losses of high protein leaf tissues. There were no definite trends in percent of in vitro dry matter digestibility (IVDMD) of leaves related to weevil damage. Lowest percentages of crude protein and IVDMD in stems and total herbage resulted when plants reached full bloom before being harvested.

Effects of host age on embryogenesis and encapsulation of the parasite Bathyplectes curculionis in the alfalfa weevil

First- through fourth-instar larvae of Hypera postica were fixed at 12- to 24-hr intervals after parasitization by Bathyplectes curculionis and sectioned histologically. Sections revealed that host age had little effect on time required for embryogenesis and hatching of parasites. B. curculionis completed larval development and emerged from all host instars ca. 11 days after parasitization at 22.2°C. Parasite eggs were fully encapsulated in just 3.3% of the first-instar H. postica compared with 50.0% in the third instar. Much larger hemocyte capsules were formed in later instars as well.

Visual Technique for Determining Presence and Stage of Zoophthora phytonomi in Dead Alfalfa Weevil Larvae12

A visual technique accurately and rapidly determines the incidence of a fungus Zoophthora Phytonomi (Arthur) Batko in dead larvae of Hypera postica (Gyllenhal). The technique is based on the presence and color of a precipitate which forms when dead larvae are placed in 3% KOH. The accuracy of this technique was confirmed by standard diagnostic procedures.

Seasonal incidence of the fungus Entomophthora phytonomi infecting Hypera postica larvae in central missouri

Seasonal incidence of the fungus Entomophthora phytonomi infecting Hypera postica larvae in central missouri

Capsule Formation in Hypera postica1 Parasitized by Bathyplectes curculionis2,3

Larvae of Hypera postica (Gyllenhal) were stung by Bathyplectes curculionis (Thomson) and fixed at timed intervals after parasitization. Encapsulation commenced 5-6 h after stinging and 40-50% of all eggs were fully encapsulated by 12-15 h. Melanization was observed in nearly all fully encapsulated eggs after 15 h. Complete encapsulation resulted in arrested embryonic development at the blastoderm stage. Some parasite embryos were killed within 21 h of parasitization. Although the rate of encapsulation (partial + complete) did not vary greatly between solitary parasitized and superparasitized weevil larvae, a greater percentage of solitary eggs were fully encapsulated and destroyed.

Insecticide Bioassays with Field Populations of Alfalfa Weevils, a Simplified Approach12

Adults and larvae of Hypera postica (Gyllenhal), were collected from the field and tested with a simplified contact biological assay with carbofuran, methidathion, phosmet, and carbaryl. Carbofuran and methidathion, with 24 h LC50 values from 0.05 to 1.39 μg/vial were the most toxic to either adults or larvae. Phosmet had a similar LC50 to young adult weevils but was much less effective against larvae. Carbaryl was ineffective in the contact tests against either adults or larvae. The simplified assay conducted without rigid control of insect age or sex or environmental parameters could be suitable for field research in agricultural entomology or for preparing test kits to provide early warning of insecticide resistance.

Photoperiodic Sensitivity of the Alfalfa Weevil During Larval Developmenet1

Larvae of Hypera postica (Gyllenhal) from the eastern United States were subjected to diapause-inducing photoperiods at various stages of development to study the relationship of photoperiod and larval development upon the induction of diapause in the adult weevil. Adults from larvae which were exposed to short-day photoperiods did not diapause, whereas adults from larvae exposed to long-day photoperiods did diapause. As little as 1 day of long-day photoperiod during larval development was sufficient to induce diapause in the adult. Adults from larvae which were subjected to an uninterrupted 16-hr photophase diapaused, whereas adults from larvae exposed to 16 hours of light which was interrupted by two 4-hour periods of scotophase did not diapause, and limited observations suggest that starvation of the larva in the late 3rd and 4th stages induced diapause in the adult.

Chemical Control of the Alfalfa Weevil in Illinois and Indiana. II. The Importance of Spray Volume in Aerial Application1

Methyl parathion and phorate were tested at rates of ½ and 1 lb of toxicant in 4 and 8 gallons of spray per acre. These materials were applied by aircraft against larvae of Hypera postica (Gyllenhal) in several tests ranging from early to late spring. Low-volume (LV) applications of technical malathion also were tested in aerial applications. Results showed that the greater volume of spray was most effective. Higher control was obtained with 0.5 lb of phorate in 8 gallons of spray than with 1 lb of toxicant in 4 gallons of spray. Results with LV applications of technical malathion were not favorable. The tendency of the material to drift, the nonpredictability of favorable temperatures, and difficulty of penetrating foliage sufficiently to come in contact with the larvae make the results of LV applications for control uncertain in southern Illinois and Indiana.