Functional response of the aphelinid parasitoid,Aphytis diaspidis:Effect of host scale species,Diaspidiotus perniciosusandHemiberlesia lataniae

Abstract

Aphytis diaspidis Howard is an idiobiont parasitoid of the invasive (Diaspidiotus perniciosus Comstock) and usual (Hemiberlesia lataniae Signoret) hosts. The objectives were to study the effect of host scale species on functional response of A. diaspidis and to answer on the question raised whether the killing efficiency of this parasitoid against the invasive host will differ from that of usual host. The parasitoid showed no host species preference with a type II response when offered both hosts at densities of 10–50 insects per patch. The proportion of hosts parasitized exhibited the same characteristic curve for the parasitoid on both hosts: a wave form that appeared to be a composite of a decelerating (type II) response at low host density and an accelerating and a decelerating (type III) response at medium to high densities. I assume that egg limitation, and/or host feeding rather than parasitism may have induced the modified type II response. The number of host parasitized within a 48 h increased with host density with a maximum of 18.3 and 18.6 adults of D. perniciosus and H. lataniae, respectively. However, the proportion of host parasitized significantly decreased with host density. This implies that the wasp seems to be more affective in low host populations. This result has to be considered in rapid population control. Estimated handling times for parasitoid were 0.98 and 1.258 h and attack rates were 0.016 and 0.02 h−1 on H. lataniae and D. perniciosus, respectively. Theoretically, the maximum number of hosts that could be parasitized by a single female within 48 h was 38.16 and 48.97 of D. perniciosus and H. lataniae, respectively. The longer time in handling D. perniciosus by a parasitoid showed that the host has lower quality than the usual host, H. lataniae. The functional response results have to be considered in both mass rearing quality testing and biocontrol programs.