Studies of a uniparental form of Aphytis vandenboschi (Hymenoptera: Aphelinidae), a parasite of the San Jose scale in northern Utah

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1 Great Basin Naturalist Volume 48 Number 3 Article Studies of a uniparental form of Aphytis vandenboschi (Hymenoptera: Aphelinidae), a parasite of the San Jose scale in northern Utah Manas Titayavan Utah State University Donald W. Davis Utah State University Follow this and additional works at: Recommended Citation Titayavan, Manas and Davis, Donald W. (1988) "Studies of a uniparental form of Aphytis vandenboschi (Hymenoptera: Aphelinidae), a parasite of the San Jose scale in northern Utah," Great Basin Naturalist: Vol. 48 : No. 3, Article 13. Available at: This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact scholarsarchive@byu.edu, ellen_amatangelo@byu.edu.

2 STUDIES OF A UNIPARENTAL FORM OF APHYTIS VANDENBOSCHI (HYMENOPTERA: APHELINIDAE), A PARASITE OF THE SAN JOSE SCALE IN NORTHERN UTAH' Manas Titayavan'"^ and Donald W. Davis" Abstract. ^The only San Jose scale parasite found at two sites in northern Utah was a uniparental form oiaphytis vandenboschi DeBach & Rosen. Parasites overwintered as pupae and were attracted to San Jose scale pheromone traps. Mature female scales were most heavily parasitized, although some prepupal males and instar II female scales were attacked. Only partial development occurred between 11.7 and 18.3 C, and fecundity was reduced between 28 and 31 C. Based on 11.7 C, 460 degree days were required in the field and 410 degree days at 26 C in the laboratory per generation. By the end of the season during 1981 at Brigham City, 30.9% of the adult scales on twigs and 79.2% on leaves were parasitized. During 1982, parasitism was 21.1% on twigs and 70.9% on leaves. A mite, Ptjemotes herfsi (Oudemans), was a major predator oiaphytis in both laboratory cultures and field populations. Field studies of the San Jose scale and its natural enemies were conducted at Brigham City and Hyde Park (near Logan), Utah, during 1981 and Laboratory studies were done at Utah State University, Logan. The more common San Jose scale parasites, such as ProspateUa { = Encarsia) perniciosi Tower (DeBach 1964) and Aphijtis aonidiae (Mercet) (Gulmahamad and DeBach 1978), were not encountered. Only one species of parasite occurred. Specimens for identification were sent to the University of California, Riverside, where they were examined by Paul DeBach, David Rosen, and Mike Rose. The initial identification given was Aphytis nr. vandenboschi (Hymenoptera: Aphelinidae), but they stated that it was probably a new species. Later correspondence indicated an inability to compare the material to specimens from the type location of A. vandenboschi; therefore, the best taxonomic designation was as uniparental forms of A. vandenboschi. Mkthods Both San Jose scales and Aphytis parasites were reared using banana squash (DeBach and White 1960) at 26.7 ± 1.5 C, 47 ± 3% RH, and using a 16-hr light: S-hr dark cycle. The scale culture was on the scjuash. Adult Aphytis were caged with the scale-infested squash. Life history studies were conducted in growth chambers at selected temperatures between 10 and 31 C. Photoperiods and relative humidities were not manipulated. All studies were replicated, although the number of replicates varied with the different experiments. Honey was supplied as adult food during all laboratory work with Aphytis adults. Experiments extending over the life span of the adult parasites began less than 12 hr after eclosion. Short-term studies were started when parasites were 2 ±.5 days old so that comparative data could be obtained near the peak oviposition period. The field studies involved time-series sampling on apple trees. This information was then correlated with temperature records within the orchards and with results of pheromone trapping. Both adult parasites and San Jose.scale males were collected readily on pheromone traps (Pherocon San Jose scale traps, Zoecon Corp.). The Brigham City orchard was an unsprayed, but cared for, backyard area of mixed fruit types. The Hyde Park orchard was an old, abandoned apple orchard of about four acres. Part of the information for life tables was obtained by lifting scales to observe the Aphytis eggs and larvae. The substrate next to the scales was mark(xl to identify.scales for sequential ()bser\ations. The population curves, shown in several figures, used third-order poknomials. This research was pari of the Ph.D. re( uir'nicnt.s al ^Utah State University, Logan. Utah Present address: Chiang Mai University. Thailand. Utah Slat' l'ni\(msity. Lotiai 388

3 July 1988 TiTAYAVAN, Davis: San Jose Scale Parasite 389 Table 1. Field parasitism of San Jose scales on apple trees by Aphytis vandenhoschi at Brigham City, Utah. Dates

4 390 Great Basin Naturalist Vol. 48, No. 3 Table 2. Partial field life table ioraphytis vandenboschi at the Brigham City apple orchard, July through August Stage of development Cause of mortality Survivors based on 1,000 k vah Eggs (n = 240) Larvae Pupae Desiccation Misc. predators^ Desiccation' Pyemotes herfsi Misc. predators Pyemotes herfsi Desiccation = ki 0.05 = ka 0.18 = k = k = k Adults (n = 5) K = 1.63 Desiccation by heat, wind, and low relative humidity. Lifting San Jose scales to examine for parasitism apparently increased desiccation ^Thrips were common at the parasite egg stage, while coccinellid adults tended to become important later European earwigs were involved but, being nocturnal, were difficult to observe. ^ 50 Q. O Hi > UJ Q O I TEMPERATURE C I 33 Fig. 1. Duration of development from egg to adult for Aphytis vandenboschi at six constant temperatures. The vertical lines show the standard error of the mean. Unidentified thrips were often associated with dead Aphytis eggs. Adult coccinellids commonly fed on both parasitized and nonparasitized scales. European earwigs consumed the entire scale, including the cover, leaving little evidence of the scales having been present. The time required for Aphytis to complete development in the laboratory is shown in Figure 1 and Table 3. At 10 C a few eggs were laid, but no embryonic development was detected. At and C there was egg hatch and some larval development. The lowest temperature showing any development was 11.7 C. The lowest temperature having complete parasite development was 18.3 C, where the cycle required an average of 38.6 days. A precise upper threshold was not determined, but 31 C was clearly above the optimum. Total eggs laid and adult longevity (Table 4) declined between 28 and 31 C. Maximum fecundity was calculated at about 26 C. The curve illustrated in Figure 1 shows the developmental rates obtained in laboratory experiments. At 31 C an average of 16.2 days was required for the full developmental cycle. Adult longevity was extremely short at higher temperatures (Table 4). The parasite had three larval instars. Measurements and time spent in each stage are shown in Table 5. These data are similar to data obtained in other studies of the genus Aphytis (DeBach et al. 1978, Rosen and Eliraz 1978). Aphytis vandenboschi showed a strong preference for adult female San Jose scales (Table 6) but apparently did not distinguish between gravid and nongravid hosts. A few prepupal males and instar II females were parasitized in the laboratory, but parasite development was incomplete. No instar I nymphs, instar II males, or pupal males were parasitized. The oviposition pattern at 23.8 C is shown in Figure 2. Oviposition peaked on day 2 with a subse(juent rapid decline on days 4 and 5. At higher tempimatiues the decline following day 2 was even more rapid. At 25.6 C little oviposition took place on day 5 and none on day 6. Figures 2 and 3 are similar, demonstrating consistency of searching ability. The percentage of scales parasitized daily (Fig. 3),

5 July 1988 TiTAYAVAN, Davis: San Jose Scale Parasite 391 Table 3. Progeny produced by 100 Aphytis vandenboschi when placed with ca 6,400 adult female San Jose scales for 24 hr, and the developmental time from egg to adult. Temperature (C) Replicated four times. Adults developing (Mean ± S.E.) : ± 11.0 Days to develop (Mean ± S.E.) eggs laid, no hatch hatch, no maturity hatch, no maturity 38.6 ± ± ± ± ± ± 0.4 Table 4. Comparative longevity of adult Aphytis vandenboschi under various constant temperatures at 47% RH and 16-hr photophase. Table 5. Developmental time and measurements of Aphytis vandenboschi immature stages, reared at 26. 7C, 47% RH, and 16-hr photophase. Temperature

6 392 Great Basin Naturalist Vol. 48, No. 3 LU C/) GC Q. a. HI Q. Q -I o LU PARASITE AGE (DAYS) Fig. 2. Influence oiaphytis vandenboschi age on number of eggs laid per female at 23.8 C. Vertical lines show the standard error of the mean. ou-

7 and G July 1988 TiTAYAVAN, Davis: San Jose Scale Parasite 393 Table 7. Number and percent of female San Jose scales parasitized by varied numbers ofaphytis vandenboschi, and their searching efficiency, in six hours at 23. 8C.' Number of para- sites Parasitism rate per Aphytis (Mean ± S.E ±0.31 a ± 0.14 b ± 0.14 b ± 0.09 c ± 0.13 c Percent parasitism (Mean ± S.E.f Searching efficiency ± 1.83 a a ± 1.71b b ± 2.50 c b ± 2.22 c c ±3. 86 d c Four replicates of 50 scales each. Data were analyzed by analysis of variance and Duncan s multiple range. Means followed by the same letter are not significantly different (5%). heavily parasitized and averaged about 75% during September The parasites in the laboratory showed partial development starting at 11.7 C, but complete life cycles were not observed below 18.3 C. The upper developmental threshold was not determined, but fecundity was reduced starting near 28 C. Using 11.7 C as the lower threshold, field data indicated an average of about 460 degree days per generation. Under laboratory conditions, at constant temperatures, a full life cycle including a preoviposition period required an average of 410 degree days. There are no records of A. vandenboschi being introduced into Utah. The introductions of this species have been reported as biparental; the adults have weak flight habits, the adult longevity is short, and rather few eggs are laid when reared on San Jose scales. This raises several questions: Why was this parasite of San Jose scales present while the more commonly encountered species were not? Is A. vandenboschi, an introduced species, the correct identity of the Utah form? Could the parasite actually be native to the region on some other scale species and then became adapted to San Jose scales? While A. vandenboschi were clearly significant biological control agents of the San Jose scale in northern Utah, they failed to achieve the level of control needed. The San Jose scale is still a major pest of Utah orchards, commonly requiring insecticidal control. Acknowledgments Identification of the Aphytis material was by Paul DeBach, David Rosen, and Mike Rose, University of California, Riverside. Identification of the Pyemotes mites was by Earle Cross, University of Alabama. Literature Cited DeBach, P Biological control of insect pests and weeds. Reinhold Publ. Co., New York. 844 pp. DeBach, P, M Rose, and D Rosen Biological and systematic studies of developmental stages in Aphytis (Hymenoptera: Aphelinidae). III. Meconia as a possible systematic tool in Aphytis. Hilgardia 46(3): DeBach. P, E B White Commercial mass culture ofthe California red scale parasite, Aphytis lingnanensis. University of California Agric. Expt. Sta. Bull pp. Gulmahamad, H, and P DeBach Biological studies on Aphytis aonidiae (Mercet) (Hymenoptera: Aphelinidae), an important parasite ofthe San Jose scale. Hilgardia 46(7): Rosen, D, and A. Eliraz Biological and systematic Varley, C G, studies of the developmental stages in Aphytis (Hymenoptera: Aphehnidae). I. Developmental history of Aphytis chilensis Howard. Hilgardia 46(3): R Gradwell, and M P Hassell Insect population ecology, an analytical approach. University of California Press, Berkeley. 212 pp.