Abstract
The ant Oecophylla longinoda Latreille forms a trophobiotic relationship with the invasive mealybug Rastrococus iceryoides Green and promotes the latter’s infestations to unacceptable levels in the presence of their natural enemies. In this regard, the antagonistic interactions between the ant and the parasitoid Anagyrus pseudococci Girault were assessed under laboratory conditions. The percentage of parasitism of R. iceryoides by A. pseudococci was significantly higher on “ant-excluded” treatments (86.6% ± 1.27%) compared to “ant-tended” treatments (51.4% ± 4.13%). The low female-biased sex-ratio observed in the “ant-tended” treatment can be attributed to ants’ interference during the oviposition phase, which disrupted parasitoids’ ability to fertilize eggs. The mean foraging time, host handling time and number of successful oviposition in “ant-excluded” treatment were significantly higher compared to “ant-tended” treatments. When ant workers were allowed access to sterilized sand grains, mummified and unmummified R. iceryoides, they selectively removed the mummified mealybugs, indicating that they recognized the mummies as potential foods (1.2 ± 0.46 to 7.8 ± 1.17 mummies at 10 min intervals for 2 h). Percentage emergence from mummified R. iceryoides removed by the ants was significantly lower compared to emergence from mummies not exposed to ants. Although, host seeking parasitoids frequently evaded attacks, some were killed by the foraging ant workers (2.0 ± 0.38 to 6.0 ± 0.88 at 10 min intervals for 2 h). These results suggest for the first time that the presence of O. longinoda has a detrimental effect on the abundance, reproductive success and possibly oviposition strategy of female parasitoids, which might be a delimiting factor in field conditions if both natural enemies are to be recommended for use within the same agro-ecosystem.
Highlights
Rastrococcus iceryoides Green (Hemiptera: Pseudococcidae) was inadvertently introduced intoTanzania, Kenya and Malawi in the early 90s, where it is potentially posing a serious threat especially on mango production [1,2,3,4]
The host range of R. invadens has been well documented with 45 plant species from 22 families classified as forest trees, vegetables, shade trees, fruit trees and ornamental plants [6] compared to more than 80 known host plants from 35 families in Southeast Asia [1,7] and 29 host plants from 16 families in Kenya and Tanzania for R. iceryoides [4]
As part of an ongoing project on integrated pest management (IPM) of major mango pests, the purpose of this study was to examine under laboratory conditions (i) the effect of O. longinoda on the incidence of parasitism of R. iceryoides by A. pseudococci and parasitoid emergence; (ii) host-handling time and oviposition success of A. pseudococci in the presence and absence of O. longinoda; (iii) effect of O. longinoda abundance on parasitoid emergence based on close examination of mummified R. iceryoides removed by the ants; (iv) assess mortality inflicted by O. longinoda on the parasitoids and behavioural responses displayed by the parasitoid to evade encounters with workers of O. longinoda
Summary
Rastrococcus iceryoides Green (Hemiptera: Pseudococcidae) was inadvertently introduced intoTanzania, Kenya and Malawi in the early 90s, where it is potentially posing a serious threat especially on mango production [1,2,3,4]. The egg stage of R. iceryoides in particular and several other mealybug species are protected by a thick waxy ovisac [4,13], which most insecticides cannot penetrate [14]. This combined with the extremely wide host range makes it almost impossible to have a spraying program capable of bearing the cost and coping with the practicalities of treating the whole range of infested plants in an affected area [15]. The most common method used by some growers is cutting down of heavily infested mango trees, while others have abandoned mango cultivation altogether
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