Mortality and growth inhibition of γ-irradiated Aspidiotus destructor (Hemiptera: Diaspididae) on mango (Sapindales: Anacardiaceae) plantlets Inamullah Khan1,*, Bitani Salahuddin2, and Habib Ur Rahman3 Abstract Aspidiotus destructor Signoret (Homoptera: Diaspididae) is a quarantine pest of mango (Mangifera indica L.; Sapindales: Anacardiaceae) and many other tropical crops. Irradiation was examined as a potential phytosanitary treatment to control A. destructor. Dose response tests were conducted with eggs, 1st and 2nd instars, pre-ovipositing adult females and ovipositing females with a series of radiation doses between 100 and 300 Gy to determine the most tolerant stage. The egg was found to be the most susceptible and adult the most tolerant stage. From probit analysis a dose of 217.7 Gy was estimated as the effective dose to completely stop scale development to subsequent stages. In large-scale validation tests 40,531 ± 79 scales in all stages were tested with 200 Gy and 51,101 ± 117 scales in all stages with 220 Gy (total = 91,633 scales). Scales did not develop to the subsequent stage when exposed to a dose of 220 Gy. We therefore propose a dose of 220 Gy for complete inhibition of development of all life stages of A. destructor that would provide quarantine security for A. destructor on exported commodities. Key Words: scale insects; phytosanitary; growth inhibition; export; quarantine pests; mango scale Resumen Aspidiotus destructor Signoret (Hemiptera: Diaspididae) es una plaga cuarentenaria de mango (Mangifera indica L.; Sapindales: Anacardiaceae) y muchos otros cultivos tropicales. Se examinó la irradiación como un tratamiento fitosanitario potencial para controlar A. destructor. Se realizaron pruebas de respuesta a la dosis con los huevos, las ninfas del primero y segundo estadio, las hembras adultas del tercer estadio sin huevos, y las hembras adultas con huevos en una serie de dosis de radiación entre 100 y 300 Gy para determinar el estadio más tolerante. Se encontró que el estadio de huevo fue el más susceptible y las ninfas de segundo estadio fue el más tolerante. De un análisis del Log dosis, se determinó que una dosis de 217.7 Gy es la dosis eficaz para detener completamente el desarrollo de la escama a los estadios posteriores. En pruebas de validación de gran escala, se analizaron con todas los estadios de escamas, 40,531 ± 79 escamas a 200 Gy y 51,101 ± 117 a 220 Gy (total = 91,633 escamas). Las escamas no se desarrollaron más cuando fueron expuestas a una dosis de 220 Gy. Por lo tanto, proponemos una dosis de 220 Gy para la inhibición completa del desarrollo de todos los estadios de vida de A. destructor y su reproducción con lo que se proveerá la seguridad cuarentenaria contra A. destructor sobre los productos básicos exportados. Palabras Clave: cochinillas; fitosanitaria; inhibición del crecimiento; exportación; plagas cuarentena; escama de mango Mango (Mangifera indica L.; Sapindales: Anacardiaceae) is grown twigs, branches and roots (Salahuddin et al. 2015; Suomi 1996; Nabity in more than 100 countries of the world (Galán Saúco 2002) and is con- et al. 2009). They cause severe damage to mango trees and depress sidered as the “king of fruits” (Tharanathan et al. 2006; Singh & Singh photosynthesis and plant respiration, inject toxins, transmit viruses 2011). It is an important fruit of tropical areas, and in South Asia it has and excrete honey dew, which serves as a growth medium for fun- been known for the last 4,000 yr (Salunkhe & Desai 1984). Mango is a gi causing sooty mold. In heavily infested trees the yield is reduced rich source of carbohydrates, vitamins A and C, iron, potassium, calci- mainly by reduced photosynthesis and respiration (Elwan 1990). Scale um and protein (Baloch 1994). In Pakistan, mango is ranked as the sec- insects may be quarantine pests and fruits infested with scale insects ond most important fruit after citrus and the third most important cash may be rejected at the port of entry. crop after cotton and rice. During 2010–2011, the area under mango Recently irradiation has been adopted as a safe measure for the crops was 117.9 km2 and its total production was 1,885,900 t. Paki- disinfestation of quarantine pests and has gained much importance stan is ranked fourth among mango producing and exporting countries in the export of agricultural fresh commodities (Heather & Hallman (Anonymous 2005). Mango is mainly exported to Dubai, Saudi Arabia, 2008). Phytosanitary irradiation has advantages over other posthar- Oman, the United Kingdom, Kuwait, Bahrain, France, and Germany. vest treatments, e.g., phytosanitary irradiation can be developed Scale insects (Hemiptera: Sternorrhyncha: Coccoidea) are very for a pest species irrespective of the host. Furthermore, irradiation important sucking pests of mango and many other plant taxa. Scale does not affect the quality of commodities at doses that nullify the insects feed on the various parts of their host plants such as leaves, pest. 1Nuclear Institute of Food and Agriculture (NIFA), Tarnab, Peshawar, Pakistan 2Department of Entomology, Faculty of Agriculture, Gomal University, Dera Ismail Khan, Pakistan 3Department of Horticulture, Faculty of Agriculture, Gomal University, Dera Ismail Khan, Pakistan *Corresponding author; E-mail: [email protected]; mailto:[email protected] Copyright © International Atomic Energy Agency 2016. Published by the Florida Entomological Society. All rights reserved. 2016 — Florida Entomologist — Volume 99, Special Issue 2 125 126 2016 — Florida Entomologist — Volume 99, Special Issue 2 Limited data are available on disinfestation of scale insects (Follett the chamber where samples were placed was conducted to verify the 2006a, b). Currently, the Government of Pakistan has adopted a radia- accuracy and range of the doses applied. The absorbed dose was mea- tion dose of 400 Gy for disinfestations of fruit flies and other insects sured using Fricke dosimeters at 3 irradiation positions (top, bottom, including armored scales (Diaspididae). Specific studies on irradiation and center) of infested plants (Table 1). Responses to irradiation doses doses that would inhibit the development of scales, reduce the risk of between 100–300 Gy of 1st and 2nd instars and adult females either damage to fresh commodities as well as reduce costs and duration of pre-ovipositional or gravid were examined. Individual plants with a treatment are required and could be used to develop a generic phyto- specific stage of the scale served as replicates and each treatment was sanitary irradiation dose for use against scale insects. replicated 3–4 times depending on the number of scales on the plants. The current study aims to determine the minimum effective irra- After irradiation, plants were transported to the Nuclear Institute for diation dose to inhibit the development of nymphs and the emergence Food and Agriculture and kept in the greenhouse at 30 ± 2 °C, and 60 ± and reproduction of adults of the coconut scale, Aspidiotus destructor 5% RH. Scales on plants were examined twice per week to determine Signoret (Hemiptera: Diaspididae). Follett (2006a) developed a phyto- the number that had developed to the next stage. As the scale body is sanitary irradiation treatment against A. destructor on fruits of Cucur- translucent and eggs are visible under the scale cover, the eggs under bita moschata Duchesne ex Poir. (Cucurbitales: Cucurbitaceae).A dose the body cover of 10 gravid females were counted using a magnifying of 150 Gy was supported via irradiation of 32,716 gravid adult females lens. Recording of data was discontinued when scales atrophied and resulting in no gravid F1 adults, although one sterile non-gravid F1 adult no longer progressed to the next stage. Untreated controls from each developed for every 23 parent generation gravid female adults irradi- stage were held under identical conditions and examined similarly. ated. This dose was accepted by APHIS (2016). The present study will use an end point that does not allow for significant 1F development, as LARGE SCALE VALIDATION TESTS that might not be acceptable to some plant protection organizations Large scale confirmatory tests were conducted to validate the es- (Hallman et al. 2010). timated dose to prevent reproduction of the most tolerant stage, i.e., the adult female. A total of 40,531, 51,101, and 43,274 adult female Materials and Methods scales were irradiated with 200 and 220 Gy and non-irradiated con- trol, respectively. Number of 1st instars and adults at F1 generation was noted for each treatment. ESTABLISHMENT OF A. DESTRUCTOR CRAWLERS ON NURSERY PLANTS DATA ANALYSIS Mango plants of uniform age and size in plastic pots of 30 × 35 Data on the effect of gamma irradiation on mortality/survival were cm were placed on mango infested plants. Branches and leaves of the subjected to analysis of variance (ANOVA) after testing for equal vari- nursery plants were attached to the infested leaves of field plants. ances and normality. Means separations were done using Tukey’s test. Some heavily scale-infested leaves from surrounding branches were All statistical analyses were done using Statistix 8.1 (Analytical- Soft cut off and wrapped around the upper portions of nursery plants. ware, Tallahassee, Florida). In addition, percentage mortality and adult When crawlers moved and settled on the nursery plants, the newly inhibition data were subjected to probit analysis using PoloPlus (LeOra infested potted mango plants were removed from the field and placed Software, Petaluma, California) to estimate the dose response of -ex in a lath house. Batches of 6–7 plants per dose were infested in the posed eggs, nymphs, and adults. same way at 4–7 d intervals. Scales on prior infested plants developed to the next stage while freshly infested plants were added into the lot. Plant infestation continued until at least 6–7 plants were infested with Results each stage of the scale. Leaves on the abaxial side were marked on plants with the specific stage of the scale.