Detection of shield beetle remains in predators using a monoclonal antibody D. Schenk and S. Bacher Zoologisches Institut, Abteilung Syno¨ kologie, Universita¨t Bern, Bern, Switzerland Ms. received: October 29, 2003; accepted: June 11, 2003 1 Abstract: Cassida rubiginosa Muell. (Col., Chrysomelidae) is considered to be a native biocontrol agent of the creeping thistle, Cirsium arvense (L.) Scop, one of the world’s worst weeds. However, predation is a major mortality factor in C. rubiginosa populations and prevents high beetle densities in nature. We determined temperature-dependent detection periods of shield beetle remains within predators by immunological gut analysis, in order to define the time period within which predation must have occurred. We conducted feeding trials with the model predators Nabis mirmicoides Costa and Chrysopa carnea Stephen at two and three different temperatures, respectively, using C. rubiginosa larvae as prey. Indirect enzyme-linked immunosorbent assay (ELISA) was used to examine the predators for the presence of prey antigen. The monoclonal antibody (MAb) CRL5-1 clearly identified predation by N. mirmicoides for up to 47 h and by C. carnea up to 96 h post-feeding at 15°C. An exponential decay gave a good description of the antigen time course within predators. Calculated detection periods for the antigen were 234.7 h at 15°C and 85.0 h at 20°C in N. mirmicoides and 215.3 h (15°C), 91.9 h (20°C) and 79.1 h (25°C) in C. carnea. The reported detection periods of prey remains in predators are the longest known in immunology, and are much higher than the recently published detection periods of prey DNA in predators. Therefore MAb CRL5-1 is a highly valuable tool for quantifying predation in the field. Key words: Cassida rubiginosa, detection period, ELISA, feeding experiments, gut content analysis, serology 2 1 Introduction Predation is not only one of the major factors affecting population dynamics of insect herbivores, but also one of the most difficult to determine and quantify. Laboratory experiments can be used to evaluate the acceptability of a particular prey and rates of preda- tion. However, these type of studies seldom translate to actual field situations where requirements of predator search are more demanding, a variety of potential prey species in changing abundances are present, and both predator and prey are subject to changing environ- mental conditions. Immunoassays using monoclonal antibodies (MAb) are an elegant way to evaluate predators in their natural environment (Kidd and Jervis, 1996). Serological studies can provide accurate data on field predation rates and the importance of a particular prey for the predator, if the detection times of prey antigen in the gut of predators and accurate estimates of predator and prey densities are obtained (Sopp and Sunderland, 1989; Kidd and Jervis, 1996). As detection periods provide a measure of the interval in which predation must have occurred, they are important for the con- struction of models to estimate predation rates in the field. The detection interval is a key parameter in most indices that have been developed to assess predation using immunoassays (reviewed by Sopp et al., 1992). Cassida rubiginosa Muell. (Col., Chrysomelidae) is considered to be a native biocontrol agent against creeping thistle, Cirsium arvense (L.) Scop (Bacher and Schwab, 2000), one of the world’s worst weeds (Holm et al., 1977). To augment and sustain the densities of natural populations of C. rubiginosa it is essential to investigate the factors responsible for the low popula- tion densities of the agents (Friedli and Bacher, 2001). Predation is a major mortality factor in C. rubiginosa populations (Schenk and Bacher, 2002), especially in late larval instars (S. Bacher and E. Kaufmann unpublished data 3 ). The actual predator species and their predation rates are known only from two study sites with the aid of video surveillance (Schenk and Bacher, 2002). However, while video surveillance gives the most accurate data on the predator complex, it is less suitable for simulta- neously screening a large number of field sites. Serology is the method of choice for obtaining a more complete picture of the predator complex of C. rubiginosa at a number of different field sites (Symondson, 2002). We recently developed an MAb to the shield beetle C. rubiginosa (Bacher et al., 1999). With this antibody we are able to examine the gut contents of field-collected predators for the presence of prey antigen by enzyme- linked immunosorbent assay (ELISA). This study reports the half-life and detection period of C. rubigi- nosa antigen at different temperatures in two model JEN 128(4) doi: 10.1111/j.1439-0418.2004.00820.273–278 Ó 2004 Blackwell Verlag, Berlin