BIOLOGICAL AND MICROBIAL CONTROL Influence of Sublethal Exposure to Abamectin on the Biological Performance of Neoseiulus longispinosus (Acari: Phytoseiidae) YUSOF BIN IBRAHIM AND TAN SEK YEE Department of Plant Protection, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia J. Econ. Entomol. 93(4): 1085Ð1089 (2000) ABSTRACT Effects of sublethal exposure to abamectin on the biological performance of Neo- seiulus longispinosus (Evans) were studied under ambient laboratory conditions of 28  2°C and 80  15% RH with 24 h light. The red form of the twospotted spider mite, Tetranychus urticae Koch, complex (Acari: Tetranychidae), was offered as prey. The LC 50 obtained from the contact bioassay at 48 h after treatment was 0.015 ppm (AI). A big change in kill for a given variation in dosage for the regression slope probably indicated that abamectin was unlikely selective. Sublethal exposures to abamectin caused a reduction in survival with the female reaching 50% mortality by the sixth day and the male 4 d later. The mean preoviposition period was extended by almost 1 d, whereas the mean oviposition period was shortened by almost 5 d causing a reduction in the mean fecundity female -1 to almost half that of the untreated females. The net reproductive rate (R o ), the intrinsic rate of increase (r m ), and the Þnite rate of increase () of the treated females were markedly inferior. Treated males were seriously affected; the mean life span was almost half that of the untreated. KEY WORDS Neoseiulus longispinosus, abamectin, bioassay, demography WORLDWIDE, CONTROL OF mites is accomplished almost exclusively with acaricides (Osborne and Oetting 1987, Parrella and Jones 1987). This is mainly attrib- utable to their effectiveness, low ratio of cost to po- tential loss, and the current lack of economical alter- native control measures (Sanderson and Zhang 1995). Because of the intensive use of chemical pesticides in agriculture, pest resurgence can take place when pes- ticide resistance develops among pest strains and im- portant natural enemies are eliminated (Waage 1989), thus invites growers on to the path of the “pesticide treadmill” (Hansen 1987). In Malaysia, the red form of the twospotted spider mite, Tetranychus urticae Koch, complex, is an impor- tant pest of Þeld crops, ornamentals, and vegetables grown under shades or screen structures. Often, local growers regulate mite populations solely with chem- icals and neglect the under-used predatory mites as agents of biological control. Among others, Neoseiulus longispinosus (Evans) (syn. Amblyseius longispinosus) has been reported to be common in orchards, Þeld crops, and nurseries in Southeast Asia (Charanasri 1994, Ibrahim and Seo 1995). A recent study revealed that this predator seemed to show promise as a bio- logical control agent of the red twospotted spider mite (Ibrahim and Abdul Rahman 1997). In view of the ever increasing emphasis on environmental friendly ap- proaches to control of pests, exploiting this phytoseiid predator as a biological control agent has become a practical way of solving acaricide resistance in the future. However, we cannot eliminate the use of pes- ticides in a short period. Phytoseiid predators alone might not be able to maintain spider mite populations below commercially acceptable levels as aptly ex- pressed by Burnett (1979) and Field and Hoy (1986). Integrated pest management (IPM) is only possible if natural enemies are not harmed by the pesticides used. Therefore, an integrated spider mite manage- ment with a workable combination of chemical and biological control tactics could be of great use. This requires the selective use of pesticides, and may be achieveable with abamectin, a compound reported to be more toxic to the spider mites than to predatory mites (Grafton-Cardwell and Hoy 1983, El-Banhawy and El-Bagoury 1985, Hoy and Cave 1985, Zhang and Sanderson 1990). As such, information about the side effects of abamectin on N. longispinosus is therefore essential. Knowledge of sublethal effects would be immediately applicable in adjusting predator-prey ra- tio in a sustainable management program. To this end, demographic toxicology has become quite a popular approach whereby ecological and toxicological pa- rameters are combined with the assumption that pre- dictions of the total effects of toxins at the population level can be elucidated (Ahmadi 1983, Stark and Wen- nergren 1995). In addition, this approach is ideal for chemicals that manifest detrimental sublethal effects on the pests and their beneÞcial species. The objec- tives of this study were to estimate the doseÐresponse of N. longispinosus to abamectin and to determine sublethal effects using life-table data. Materials and Methods Chemical Tested. Abamectin (AGRIMEC 1.8 EC, Kuala Lumpur, Malaysia) was used in this study. Serial 0022-0493/00/1085Ð1089$02.00/0  2000 Entomological Society of America Downloaded from https://academic.oup.com/jee/article/93/4/1085/2217227 by guest on 13 January 2023