Effects of diflubenzuron on black vine weevil oviposition, egg viability and adult longevity (Coleoptera: Curculionidae).

Adult black vine weevils, Otiorhynchus sulcatus (F.) were fed 3 concentrations of diflubenzuron (0.05, 0.025, and 0.013 g Al/liter) sprayed on the foliage of yews, Taxus media Reh der. Fecundity of those insects exposed to diflubenzuron was re duced 15-81% compared to that of insects fed nontreated foliage. Reduction of fecundity was caused by decreased oviposition and egg viability. Diflubenzuron did not affect adult longevity. Diflubenzuron (N(((4-Chlorophenyl) amino) carbonyl)-2, 6-difluoroben zamide; Dimilin?; Thompson-Hayward 6040) has shown varying insecticidal properties among a number of insects. Ovicidal and/or sterilant activity following adult exposure has been demonstrated in certain coleopterans (Taft and Hopkins, 1975; McGregor and Kramer, 1976; Calkins et al., 1977; Tedders, 1977) but not among parthenogenetic species. The black vine wee vil, Otiorhynchus sulcatus (F.) is a parthenogenetic species in which the reproductive system does not mature until 4-10 weeks after adult eclosion (Smith, 1932; Cram, 1958). Adults feed voraciously on foliage during repro ductive maturation, and their feeding, combined with larval damage to plant roots, makes the species one of the more serious pests of ornamental plants in many northern states and also in areas of Canada. Adults live up to 617 days and may produce >1600 eggs (Smith, 1932). Therefore, our experi ments were designed to detect effects of diflubenzuron on black vine weevil oviposition, egg viability, and adult longevity. Methods and Materials Newly emerged black vine weevil adults were collected 15 June 1977, in a yew planting of a Suffolk County, New York nursery. They were taken to our laboratory in Ithaca, placed in 10-cm disposable petri dishes, 5/dish, and fed Taxus media Rehder cuttings which were replaced daily. Each dish was designated as a replicate, and three replicates were assigned per treat ment. The insects were held in a growth chamber at 28?C, with a 12:12 h photoperiod. Received for publication 20 October 1978. This content downloaded from 157.55.39.147 on Wed, 18 May 2016 05:32:40 UTC All use subject to http://about.jstor.org/terms VOLUME 52, NUMBER 4 663 Three aqueous suspensions of Dimilin 25 WP (0.05, 0.025, and 0.013 g Al/ liter) were applied 20 June 1977, each to one of 3 large (ca. 4-m diameter), multi-plant, isolated blocks of T. media located near our laboratory. A fourth planting was sprayed with distilled water at the same time to serve as a check. All sprays were applied with a Solo? backpack sprayer until runoff. Beginning immediately after the foliage was dry, random foliar samples (ca. 7 cm long) were collected daily from the sprayed areas on each of the 4 plantings and placed in the appropriate dishes to feed the test weevils naturally aging diflubenzuron residues. Dead weevils were removed, all eggs present in the petri dishes or on the foliage were counted, and sprayed foliage was replaced daily. When all weevils in a replicate died, the total number of eggs in that replicate was divided by the cumulative number of live weevils present during each 24 h period, and is expressed as eggs/9 day. The total experimental period was then divided into 5-day intervals, and eggs/9 day calculated for each interval to evaluate treatment effects on oviposition cycles. If fewer than 50 eggs replicate were found during daily counts, all were held to determine the hatch percentage; if more than 50 were present, 50 were randomly selected for observation and the excess counted and dis carded. The eggs to be observed were placed in 30-ml styrene cups con taining 15 ml of hardened plaster of Paris saturated with distilled water. The cups were closed with tight-fitting plastic lids, and held in complete darkness at 28?C, except during observations of hatch. Observations began when the eggs were 9 days old, and continued daily until hatching ceased. All larvae were removed from the cups and discarded when counted. Total hatch per centages and 5-day interval hatch percentages were calculated after all wee vils in a replicate died, and hatch had ceased. Adult longevity is expressed as the mean number of days survived after the weevils' first exposure to treated foliage. We have not included the insects' pre-experimental ages in the longevity data, because we could not assess the intervals between their eclosion and emergence, which may range 4-17 days (Smith, 1932). Following arcsin transformation of the hatch per centages, all data were subjected to analysis to variance and least significant difference mean separation procedures. Results and Discussion Diflubenzuron had no observable effects on T. media, and treated foliage was readily eaten by the weevils. When presented in the manner described, diflubenzuron did not cause significant differences in longevity among the experimental insects (Table 1). The first eggs were found 12 days after the insects' exposure to treated foliage; the last were found 77 days after exposure. The total numbers of This content downloaded from 157.55.39.147 on Wed, 18 May 2016 05:32:40 UTC All use subject to http://about.jstor.org/terms 664 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY j-1-1-1-1-1-1-1 I 4 a * I 1 L\ / \ ? CHECK I "7 NX/ \ ?*0.013g Ai/I 1(4 / / X**^-. \ o?oa025gA./| 1 // \ \ u?u0-05g Ai/I |Cb?-,-,-,-,-,-,-n >ft-??*-1 10 30 50 70 DAYS AFTER ADULT EXPOSURE I-1-1-k-1-1-1-1-1-1-1-1-1 R /\ ? CHECK / \ *?*0.013g Ai/I I / A\ o?o0.025g Ai/I I 60| I i\ \ ?"" u0058 Al/| f tAra y UVM DAYS AFTER ADULT EXPOSURE Fig. 1. Five-day interval effects of diflubenzuron on black vine weevils, A: no. eggs/9 day B: % egg hatch. This content downloaded from 157.55.39.147 on Wed, 18 May 2016 05:32:40 UTC All use subject to http://about.jstor.org/terms VOLUME 52, NUMBER 4 665 Table 1. Laboratory bioassay effects of diflubenzuron on oviposition, egg viability, and longevity of black vine weevil adults. Each mean represents the performance of 15 insects. Treat~ ~ . , * Eggs/9 day Egg viability ment Total Adult Relative g Al/ eggs Fraction Hatch Fraction longevity fecun liter (no.) No.* of check (%)* of check (days)* dity** 0.05 1,869 2.41a 0.45 19. la 0.42 59.8a 0.19 0.025 2,238 2.61a 0.48 19.5a 0.49 67.7a 0.24 0.013 5,525 4.89b 0.91 43.2b 0.93 79.8a 0.85 check 4,992 5.40b 1.0 44.8b 1.0 67.0a 1.0 * Within-column means followed by the same letter do not differ significantly at the 5% level of probability. ** Relative fecundity = (eggs/9 day fraction of check) x (egg hatch fraction of check). eggs/9 day laid by the weevils fed 0.05 and 0.025 g Al/liter were signifi cantly less than in the check (Table 1). The ovipositional cycles observed in the check are similar to those reported by Penman and Scott (1976), i.e., a rapid increase in the number of eggs/9 day, followed by a sharp decrease and a series of subsequent fluctuations of lower magnitude (Fig. 1A). The weevils fed 0.05 and 0.025 g Al/liter had similar oviposition cycles, but laid fewer eggs. Eggs laid by weevils fed diflubenzuron at 0.05 and 0.025 g Al/liter were significantly less viable than eggs laid by the check weevils. As the study progressed, viability decreased in all treatments including the check, but diflubenzuron treatments were generally lower (Fig. IB). Egg viability in the check was lower than that reported in other studies (Cram and Pearson, 1965; Cram, 1967; Shanks and Finnigan, 1973), but approximates that re ported by Cram (1965) when black vine weevils were fed nitrogen-deficient strawberry foliage. Cram (1967) reported that apholate-induced sterility of black vine weevils was reversible. Our studies show slight resurgences of oviposition and egg viability among the treated weevils very late in the experiment (Fig. 1), however, few weevils were alive at that time, making those data extremely variable. The cumulative effects of diflubenzuron on oviposition and egg viability are given in Table 1 as "relative fecundity." This was much reduced among those weevils fed diflubenzuron at the 0.05 and 0.025 g Al/liter rates, due to the decreased hatch of fewer eggs than in the check. This net reduction in weevil fecundity clearly demonstrates a potential means of reducing black vine weevil population levels by interference with normal reproductive cycles and suggests that diflubenzuron may similarly affect other parthenogenetic insects. This content downloaded from 157.55.39.147 on Wed, 18 May 2016 05:32:40 UTC All use subject to http://about.jstor.org/terms 666 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY