Rhopobota Naevana Research Articles

Modeling of Blackheaded Fireworm (Lepidoptera: Tortricidae) Oviposition and Pheromone-Trap Catches

Our objectives were to predict pheromone-trap catches and oviposition of blackheaded fireworm, Rhopobota naevana (Hübner), on commercial cranberry farms in Wisconsin, Washington, Oregon, and British Columbia and to model oviposition in Wisconsin. Real time, expressed as days after male moths were caught in traps, predicted the day of 50% catch better than degree-days in both growing regions. Weibull functions were used to model the cumulative percentage of male moths caught and cumulative percentage of eggs laid over time in a Wisconsin cranberry farm not treated with insecticides and the percentage of catch of male moths on insecticide-treated farms in Wisconsin and the Pacific Coast growing region. Insecticide treatments made the patterns of flight activity less predictable. However, characteristics of flight activity common to all regions indicated oviposition may occur during a 4-wk period after first catch.

Blackheaded Fireworm (Lepidoptera: Tortricidae) Larval Phenology Model Based on Diet-Specific Developmental Rates

Phenology of blackheaded fireworm larvae, Rhopobota naevana (Hubner), was simulated with developmental rate-summation models. The relationship between temperature and median developmental rates of third instars and pupae were determined by using linear splines. Variation in developmental rates within a population was determined by using Weibull functions. Phenology of summer-generation larvae was simulated in multiple weekly cohorts starting from the estimated times eggs were laid. The model predicted within an average of 1 d (σ = 3.6 d) the date when 50% of the larvae in the field were past the second stadium. Development of larvae in the spring was predicted starting from the time of hatch of sampled eggs. The model included lower developmental rates and higher mortality before new leaves were available. When diet was included in the model, it predicted the date when 50% of the spring-generation larvae was past the second stadium within an average of 2.5 d. The models for the spring and summer generations were sensitive to the estimated dates of egg hatch and oviposition, respectively.

Hatch of Blackheaded Fireworm (Lepidoptera: Tortricidae) Eggs and Prediction with Temperature-Driven Models

Egg hatch of blackheaded fireworm, Rhopobota naevana (H¨bner), was monitored in Wisconsin and British Columbia. In Wisconsin, hatch of overwintering eggs began during the last 2 wk of April, median hatch occurred during the first week of May, and hatch ended in late May. In British Columbia, hatch began in late March to early April, median hatch occurred in April, and hatch ended (except for one egg in both years that hatched in June) in late April in 1991 but extended into late May in 1992. Summer-generation eggs began hatching 2–7 d and completed hatch 6–15 d after oviposition in both regions. A linear spline model developed in Wisconsin predicted 50% hatch of overwintering eggs in Wisconsin to within ±5.5 d standard deviation. The model had extreme error in predicting hatch in British Columbia. A linear model predicted 50% hatch of summer-generation eggs in both Wisconsin and British Columbia to within ±1d standard deviation.

IndigenousTrichogramma (Hym.: Trichogrammatidae) parasitizing eggs ofRhopobota naevana (Lep.: Tortricidae) on cranberries in British Columbia

Two indigenous species ofTrichogramma were reared from natural populations of the blackheaded fireworm,Rhopobota naevana (Hubner) infesting cranberries in British Columbia, Canada. One was identified asTrichogramma sp. nr.sibericum Sorokina and the other wasTrichogramma minutum Riley. Percentage of parasitized hosts increased during the season in an abandoned field, but decreased in a commercial field where pesticides were used. The potential ofTrichogramma as a biological control agent against the fireworm is discussed.

Fecundity, Number of Diapause Eggs, and Egg Size of Successive Generations of the Blackheaded Fireworm (Lepidoptera: Tortricidae) on Cranberries

This study was conducted to assess the reproductive potential of first- and second-generation Rhopobota naevana (Hubner) females collected from a commercial cranberry farm and reared on field-collected foliage under controlled conditions. Between 90 and 95% of eggs laid by first-generation females hatched within 2 wk of oviposition, whereas most (80–95%) eggs laid by second-generation females entered diapause. In 1990, when cranberry plants were heavily fertilized with nitrogen, total fecundity of the two generations was similar. In 1991, when a minimal amount of nitrogen fertilizer was applied to the plants, first-generation females were more fecund than second-generation females, and diapause eggs laid by second-generation females were larger than nondiapause eggs laid by first-generation females. Ovarian maturation proceeded more slowly in the second generation than in the first. Duration of pupal stage, adult stage, and emergence period were longer in the second generation than in the first. Male pupae weighed less than female pupae, and males emerged slightly before females. Results suggest that first-generation fireworm females allocate resources gathered during larval feeding to production of as many eggs as possible, whereas second-generation females produce fewer, larger eggs. However, second-generation females fed nitrogen-rich foliage may be able to produce more eggs than usual.

Consequences of Feeding Site Selection on Growth and Survival of Young Blackheaded Fireworm (Lepidoptera: Tortricidae)

Young blackheaded fireworm, Rhopobota naevana (Hubner), feed on old leaves or, when available, new leaves of cranberry, Vaccinium macrocarpon Aiton. In laboratory choice experiments, first-instar caterpillars preferred new leaves to old leaves regardless of temperature and photoperiod or generation of larvae. In no-choice tests, more larvae died before feeding (61.4%) when exploring dormant cuttings with only old leaves than did those exploring growing cuttings (11.8%). Larvae continued to reject old leaves and climb to the top of shoots even when deprived of food. Duration of the first stadium was 65% longer on overwintered leaves compared with young leaves. Survival of larvae in commercial cranberry marshes was 4.9 times greater after new shoot growth than survival of larvae hatched before new growth.

Hatch of Eggs of Overwintering Blackheaded Fireworm (Lepidoptera: Tortricidae) in Response to Duration of Winter

Eggs of overwintering blackheaded fireworm, Rhopobota naevana (Hubner), were collected from cranberry marshes in Wisconsin and Washington. Eggs were held at a naturally progressing photoperiod (for 45 degrees latitude) and constant cold temperatures representing winter conditions in the two states: -2 degrees C for Wisconsin and 5 degrees C for Washington. On five different dates in March, April, and May, sets of eggs were incubated at 18 degrees C while natural photoperiod was maintained. The first three groups of eggs from Wisconsin showed no difference in development rate upon incubation. The fourth group, transferred about mid-April, developed faster than previous groups. The fifth group developed fastest. The first group of eggs from Washington, incubated in early March, developed slowest. The remaining groups, incubated about mid-March and thereafter, developed and hatched at the same, more rapid, rate.

Flooding Cranberry Beds To Control Blackheaded Fireworm (Lepidoptera: Tortricidae)

Survival of larvae of blackheaded fireworm, Rhopobota naevana (Hübner), was determined in two experiments where insects were submerged in water of different temperatures or dissolved oxygen content. Water temperature at high (8.2-13.1 ppm) dissolved oxygen did not affect survival significantly; 47% survived at 2°C and 41% at 10°C after 9 d. Dissolved oxygen affected survival significantly; only 7% survived in water oflow dissolved oxygen (5.1-7.1 ppm) at 10°C for 3 d compared with 91% at high dissolved oxygen (8.8-9.8 ppm). Flooding to control fireworm larvae was evaluated on three commercial cranberry marshes. A 25-50-h spring flood while vines were dormant resulted in a significant reduction of larvae. Data show that flooding may be useful to manage blackheaded fireworm.

Relative Efficacies of Two Commercial Pheromone Blends for Monitoring the Blackheaded Fireworm (Lepidoptera: Tortricidae) of Cranberries

Two commercial pheromone blends are available for monitoring the blackheaded fireworm of cranberries, Rhopobota naevana (Hubner). Results from the 1st yr of a 2-yr field test showed that the three-component blend (69.2% (Z)-ll-tetradecen-l-ol acetate, 23.1% (Z)-ll-tetradecen-l-ol, and 7.7% (Z)-9-dodecen-l-ol acetate, at a total loading of 1 mg per septum) tended to attract more males to traps than the two-component blend (98% (Z)-ll-tetradecen-l-ol and 2% (Z)-9-dodecen-l-ol acetate, at a total loading of 2 mg per septum). Results in the 2nd yr showed that the three-component blend was significantly more attractive than the two-component blend. The dates of early and maximum catches were independent of blend composition in both years.

Blackheaded fireworm: Laboratory and field studies of its sex pheromone

Electroantennogram (EAG) responses of maleRhopobota naevana (Hübner), the blackheaded fireworm, to all of the monoene straightchain 12- and 14-carbon alcohols and acetates implicated (Z)-11-tetradecenl-1-ol (Z11-14∶OH) and its acetate (Z11-14∶Ac) as sex pheromone components.Z11-14∶Ac produced the strongest EAG response of all compounds tested. Gas chromatography-mass spectrometry (GC-MS) analysis of extract of female sex pheromone glands (SPG) confirmed the presence ofZ11-14∶OH (125 pg/female) andZ11-14∶Ac (600 pg/female) (all other monoenes had different retention times). In field tests, traps baited withZ11-14∶OH alone captured males, but traps baited withZ11-14∶Ac alone did not. Traps baited with a combination ofZ11-14∶OH andZ11-14∶Ac in various ratios did not produce better trap catches thanZ11-14∶OH alone. (Z)-9-Dodecen-1-ol acetate (Z9-12∶Ac), reported by others to be a field attractant, did not produce trap catch in our tests, but in combination withZ11-14∶ OH (98∶2 in septa corresponding to 95:5 in vapor,Z11-14∶OH toZ9-12∶AC) produced a sevenfold increase in catch overZ11-14∶OH alone. IfZ9-12∶AC had been present in extract of SPG at 2-5% ofZ11-14∶OH, it would not have been detected in our GC-MS experiment.

Sex pheromone of blackheaded fireworm,Rhopobota naevana (Lepidoptera: Tortricidae), a pest of cranberry

Splitless capillary gas chromatography indicated the presence of (Z)- and (E)-11-tetradecenyl acetate and (Z)-11-tetradecenyl alcohol in the washes of female abdominal tips of the blackheaded fireworm,Rhopobota naevana (Hubner). Gas chromatography combined with mass spectroscopy confirmed the presence of tetradecenyl acetate in extracts of female tips. The low levels observed in these extracts (< 1 ng/female equivalent), prevented further chemical and spectroscopic identification. These materials were found to be stimulatory at low levels in electroantennogram studies. A combination of 9 μg of (Z)-11-tetradecenyl acetate and 3 μg of (Z)-11-tetradecenyl alcohol on rubber septa in wing traps provided an effective attractant. (Z)-9-Dodecenyl acetate, a previously reported attractant, did not significantly increase field trapping catches when added to the binary mixture, but was found to enhance trap catches when added to each of the primary components.

The Blackheaded Fireworm of Cranberry—A Pest of the Evergreen Huckleberry in Western Washington1

Moths identified as adults of the blackheaded fireworm of cranberry, Rhopobota naevna (Hbn.), were obtained from larvae that were very destructive to the "evergreen huckleberry," Vaccinium ovalum, Pursh., on the Olympic Peninsula in Washington in 1958 and 1959. These larvae are known locally as "tipworms" from their habit of feeding on the terminal growth of the young shoots of the host plant. The "evergreen huckleberry" is a new host for host for the blackheaded fireworm in America. Previously it was known only from cranberry. Two parasitic insects were reared from the "tipworms," an ichneumonid wasp, Horogenes sp., and a tachinid fly, Eulasonia sp. Both are now records. The parasitic wasps killed the "tipworms" in the last larval stage and destroyed about 10% of them. The synonomy of the blackheaded fireworm is questioned and reasons for this uncertainty are given.

Holly Bud Moth Control1

The holly bud moth, Rhopobota naevana (Hbn.) Kearfott, was introduced into British Columbia before 1923 and has subsequently spread southward through Washington into Oregon. It is now an important pest in Oregon holly plantings. Evaluation of insecticides for holly bud moth control showed that a high degree of control can be obtained with organic phosphate insecticides. Malathion consistently provided excellent control with one spray applied sometime between the opening of the leaf buds and the time of blossoming. Good control was also obtained with methoxychlor. DDT did not give consistent results under the same conditions. The difference between the results with the organic phosphates and with DDT might be explained on the basis of DDT tolerance in the holly bud moth. Another possible explanation is that the organic phosphate insecticides have an ovicidal effect which DDT does not have. The results with methoxychlor make the first explanation more probable.