It can be reared on some alternative hosts such as eggs of Podisus maculiventris (Say). ... response of female wasps that emerged from the factitious host, ...
JEN 128 (2004) J. Appl. Ent. 128, 39–43 (2004) 2004 Blackwell Verlag, Berlin ISSN 0931-2048
Effects of host on functional response of offspring in two populations of Trissolcus grandis on the sunn pest H. Allahyari, P. A. Fard and J. Nozari Department of Plant Protection, College of Agriculture, University of Tehran, Karaj, Iran Ms. received: February 18, 2003; accepted: June 05, 2003
Abstract: Trissolcus grandis Thompson is the most important egg parasitoid of Eurygaster integriceps Put. in Iran. It can be reared on some alternative hosts such as eggs of Podisus maculiventris (Say). In this study, the functional response of female wasps that emerged from the factitious host, P. maculiventris, has been compared with that of females that emerged from the primary host, E. integriceps. In both wasp groups, at 23 ± 1C, 70 ± 10% relative humidity and 15.00 : 9.00 hours (L : D) photoperiod, a type III functional response was observed. Parameters of Holling’s disk equation for both populations were estimated and compared with an equation with indicator variable. Estimated handling time for females that emerged from Eurygaster and Podisus eggs are 0.62 and 0.77 h and parameter b, which describes the change in attack rate with host density in a type III functional response, was 0.004 and 0.005, respectively. The results indicated that the functional responses of the two populations differed in handling time. Longer handling time in wasps that emerged from factitious host showed that the wasps have lower quality in comparison with the wasps that emerged from primary host. This may be the first evidence of the effect of host on functional response of offspring and a promising result for use of functional response in quality testing.
Key words: Eurygaster integriceps, Podisus maculiventris, Trissolcus grandis, functional response, Holling’s disk equation, quality control
1 Introduction The sunn pest, Eurygaster integriceps Put., is the most important pest of wheat in Iran and the Middle East. The pest has one generation per year with an obligatory diapause. During early spring, overwintering adults arrive at the field, and after feeding, begin to lay eggs. This pest can cause qualitative and quantitative damage to wheat and barley (Radjabi, 2000). The sunn pest is controlled by some parasitoids from the families Scelionidae (Hymenoptera) and Tachinidae (Diptera). Among these parasitoids, Trissolcus (Scelionidae) gets more attention from Iranian entomologists. Mass rearing of Trissolcus on sunn pest eggs is difficult because the host is univoltine, and the availability of an alternative host could be a solution to this problem. A good alternative host must be able to produce high numbers of eggs throughout the year and its eggs must be accepted by the parasitoid. Suntsova and Shirinyan (1974) revealed that Graphosoma lineatum L. is a suitable host for Trissolcus grandis Thompson and Trissolcus simony Mayr. Shahrokhi (1997) tried to rear G. lineatum on seeds of umbelliferous plants such as Heracleum persicum and Foeniculum vulgare and used its eggs as an alternative host for Trissolcus. He reported a negative attribute for laboratory-reared bugs; there was a significant difference in the mean number of eggs among females U. S. Copyright Clearance Center Code Statement:
collected in late spring and summer (461.8) compared with laboratory-reared generations (53–104). Allahyari (1999) tried to rear T. grandis and Trissolcus vassilievi Mayr. on Podisus maculiventris (Say) eggs. There are some studies that report on the parasitism of Podisus by scelionid wasps (Yeargan, 1979; Orr et al., 1986; Colazza et al., 1996). Allahyari (1999) successfully reared two species of Trissolcus on Podisus eggs; he indicated that the waspsÕ progeny was about 11 and 7% (for T. grandis and T. vassilievi, respectively) smaller than wasps which had emerged from Eurygaster eggs and these differences were significant from a statistical point of view. This difference raises the question as to whether the killing efficiency of these parasitoids reared from alternative hosts will also be different from that of wild wasps. Differences in killing efficiency between two parasitoid or predator populations can be compared by estimation and comparison of functional response parameters (Livdahl and Stiven, 1983; Juliano and Williams, 1985; Juliano, 2001). In this study, we determine if there is any difference between functional response of wasps that emerged from Eurygaster eggs and others emerging from Podisus eggs. Functional response is defined as the change in number of parasitized hosts in relation to change in
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H. Allahyari, P. A. Fard and J. Nozari
host density (Cave and Gaylor, 1989). Among the three types of functional response, type II and III have received the most attention. The most widely used model for describing the functional response of predator/parasitoid is the disk equation of Holling (1959): Na ¼
aTt N0 1 þ aTh N0
ð1Þ
where Na is the number of host attacked, N0 the initial number of hosts, Tt the time of exposure, a the rate of successful attack and Th the handling time. For modelling the type III functional response, attack rate (a) must be set in equation 1 as a function of prey density. In the simplest generalized form, attack rate is a function of initial number of prey/host density: a¼
d þ bN0 1 þ cN0
ð2Þ
in which b, c and d are constants that must be estimated.
(2, 4, 8, 16, 32, 64, 128) of E. integriceps eggs (
