Influence of the host plant on the encyrtid Aenasius bambawalei, a parasitoid used to control the cotton mealybug, Phenacoccus solenopsis, in Pakistan

Abstract

The mealybug Phenacoccus solenopsis Tinsley (Sternorrhyncha: Pseudococcidae) is a highly polyphagous pest of fruits, vegetables, crops and ornamentals in Pakistan. Biological control approach by using Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae) has been developed recently to control this pest. However, the efficiency of this parasitoid is variable according to the locality and the plants on which P.solenopsis is feeding. In this context, this experiment investigated under field and laboratory conditions the influence of the host plant of P. solenopsis on the parasitism success and the female fitness of A. bambawalei, Five plant species, commonly found to be host of P. solenopsis, were tested: hibiscus, potato, okra, eggplant and tomato. Under no choice test conditions, the results showed that the % parasitism did not differ significantly between different host plants in laboratory and field conditions. In contrast under multiple choice test conditions, the % parasitism (65.00±3.75, 60.00±2.83, 51.88±1.88, 69.38±2.54, 60.63±2.80 under field conditions and 63.13±2.71, 61.25±2.60, 49.38±2.54, 68.13±2.37, 53.75±2.5 under lab condition for okra, tomato, brinal, hibiscus and potato respectively) significantly differed between plants showing higher parasitism on hibiscus as compared to the other plant species tested. Moreover, the % parasitism generally decreased drastically when the time of exposure on mealybug hosts increased. In addition, the host plants species influenced significantly the female fitness of the parasitoid expressed in term of hind tibia length and body weight. The female parasitoids coming from mealybugs fed on hibiscus exhibited a significantly longer tibia and body weight than the parasitoids coming from the mealybugs reared on the other plants. The host plants did not influence the sex ratio of the 3rd trophic level. The current study indicated that hibiscus is, among those tested in this study, the best plant species to mass rear the mealybug and its associated parasitoid in a context of biological control program. However, additional research is needed to assess the properties of hibiscus to attract the parasitoid