Functional Response of Chelonus Oculator (Hymenoptera: Braconidae) to Temperature, and Its Consequences to Parasitism

COMMUNITY ECOLOGY 9(1): 45-51, 2008 20081585-8553/$20.00 © Akadémiai Kiadó, Budapest DOI: 10.1556/ComEc.9.2008.1.6 Functional response of Chelonus oculator (Hymenoptera: Braconidae) to temperature, and its consequences to parasitism M. García-Martín1, M. Gámez2, A. Torres-Ruiz1 and T. Cabello1,3 Department of Applied Biology, Almeria University, Ctra. de Sacramento s/n, 04120-Almeria, Spain Department of Statistics and Applied Mathematics, Almeria University, Spain ! Corresponding author. Fax: +34-950015476; Phone: +34-950015001, E-mail: [email protected] Keywords: Biological control, Egg-larval parasitoid, Ephestia kuehniella, Handling time, Lepidoptera, Mathematical models, Spodoptera exigua. Abstract: The parasitization behaviour of Chelonus oculator (F.), egg-larval parasitoid of noctuid lepidopteran species, has been studied under laboratory conditions, using Ephestia kuehniella Zeller as host, at four different temperature levels (10, 20, o 30 and 40±1 C) and five densities of host eggs (50, 100, 150, 200 and 250). A significant effect of temperature and parasitism o o density was observed. At 10 C, there was no parasitism, whilst at 40 C it was very low; presenting adequate values at the two o other temperatures (20 and 30 C). With regard to these facts, the functional responses of this parasitoid species were adjusted and we noted that they display Holling type III. Estimating the handling times from the respective mathematical expressions, o we obtained 10.944 and 15.250 min, at 20 and 30 C, respectively. These values are considerably higher than the respective times obtained by direct observation, 0.597 and 0.560 min for these temperatures (this difference is due to the fact that in the first case, unlike the second one, the time used for the search of the host is also included). The results obtained from the parasitization behaviour of Ch. oculator are discussed, also considering it as a candidate biological control agent against Spdoptera exigua (Hübner), beet armyworm, with a view to its possible use in greenhouse crops in Spain. Introduction bello et al. 1996). In the case of S. exigua, the parasitoid egg- Spodoptera exigua (Hübner), beet armyworm, is one of larval species that stands out is Chelonus oculator (F.) (Pino the most devastating pest in Spanish greenhouse crops, espe- et al. 2003) which could potentially be a control agent in cially in pepper and water melon (Cabello and Belda 1994, greenhouse crops if increased. We need to point out that the Cabello 2004). The development of biological control meth- functional response offers a good basis to understand the ac- ods against noctuid pests in these crops, with the only excep- tion of entomaphagous agents in biological control pro- tion of Bacillus thuringiensis Beliner, has hardly been com- grammes (Waage and Greathead, 1988; Barlow, 1999), al- pared with that for outdoor crops; as for example, with beit with restrictions as described by Mills and Getz (1996); species of Trichogramma (van Lenteren 2000). To be spe- admitting in addition a biological interpretation of the pa- cific, the allochthonous larval endoparasitoid species Cotesia rameters of the functional response (Cabello et al. 2007). marginiventris (Cresson), has been trialled in greenhouse Thus, when it comes to “classical” biological control, one in- conditions for the control of S. exigua (Messelink 2002, Ur- tends to introduce an allochthonous natural enemy to a new baneja et al. 2002) as well as Baculovirus (SeMNPV) both geographic area, where its prey/host has been previously de- allochthonous (Moscardi 1999, Smits and Vlak 1994), and termined, in order to exert a natural control similar to that autochthonous (Belda et al. 2000). they performed in their area of origin. This operation requires a certain stability of the predator-prey (or parasitoid-host) The lack of commercially available natural enemies for system, which can only be reached with a natural enemy the control of S. exigua, together with the problems of resis- showing type III functional response. The latter is the only tance to insecticides of this pest in our area (Smagghe et al. type considered adaptive depending on the density of the host 2003), constitute a restraining factor for the application of and with good potential for regulating the host population biological control programmes or IPM, in greenhouse crops (Hassell and May 1973, Oaten and Murdoch 1975a,b, (van der Blom 2002), especially in S. exigua (Castañé 2002). Hassell 1978). Contrary to this, in case of inundative biologi- On the other hand, in the outdoor crops of the area, cal control, stability of the system is not important, since our parasitoid and predator species (Cabello 1986, 1988, Cabal- objective then is to get a short-term response, due to the fact lero et al. 1990, Guimaraes et al. 1995, Torres-Villa et al. that the mortality of the prey/host occurs before a generation 2000) as well as entomopathogens (Caballero et al. 1992) are is completed. In this case, in principle, a type I response very abundant and provide very efficient control over the seems to be more adequate, in which there is a linear response pest populations, with elimination rate of 33 and 100% (Ca- between the density of the phytophagous insect and the mor- bello 1988), which does not happen in greenhouse crops (Ca- tality caused by the entomophagous insect. In this sense, 46 García-Martín et al. Jeschke et al. (2004) point out that a type I functional re- For each temperature at which adequate parasitization sponse is due to two fundamental conditions: a very short values were found, the type of functional response presented manipulation time and a maximal activity state, long enough was determined. First of all, a distinction was made between to reach saturation. This is the case in the majority of the spe- functional response types II and III, estimating the cubic and cies of the genus Trichogramma, which are globally used in quadratic linear parameters in the following equation pest control (van Lenteren 2000, Elzen et al. 2003): they usu- (Juliano 2001): ally follow type I functional response (Cabello 1985, Faria et N exp(PPNPNPN+⋅ +⋅2 +⋅3 ) al. 2000, Mills and Lacan 2004). For all these reasons, the a = 01tt 2 3 t (1) N 1++⋅+⋅+⋅exp(PPNPNPN2 3 ) objective of this study is to establish the functional response t 01tt 2 3 t of this parasitoid and the effects of temperature to complete where Na is the number of parasitized hosts, Nt is egg host its assessment as a potential biological control agent for S. density, Po,P1,P2 and P3 are adjustment parameters. exigua in greenhouses in Spain. Subsequently, the data were adjusted to the equation for parasitoid type III functional response, established by Materials and methods Hassell 1978, according to the following expression: In all the trials carried out in laboratory conditions, Ch. L F bT⋅⋅ N ⋅ P IO NN=⋅−M1 expG − tt JP (2) oculator mated females were utilised which had emerged at H 2 K NM 1+⋅cNtht +⋅ bT ⋅ N QP from the pupa less than 48 hours before and without previous parasitization experience; as well as eggs less than 24 hours old from the alternative host, Ephestia kuehniella Zeller. In where Na and Nt are as before, T is available time for search- both cases, the specimens came from the populations kept in ing (days), Th is the estimated handling time of the host the Agricultural Entomology Laboratory of the University of (days), Pt is the number of parasitoids, b, c are adjustment Almeria. In the first species, breeding was carried out follow- parameters. ing the methodology of Cabello et al. (2005), and for the sec- All the previous models were adjusted by non-linear re- ond one, the methodology utilised was that of Daumal et al. gression and the Marquardt algorithm (Conway et al. 1970), (1975) and Rodríguez et al. (1988a,b). using the programme GraphPad Prism version 4.00 (Motul- sky and Christopoulos 2003) The trial was factorial, with two treatments: temperature o (at four levels: 10, 20, 30 and 40±1 C) and host density (5 Once the type of functional response had been selected, levels: 50, 100, 150, 200 and 250 E. kuehniella eggs), carry- in order to verify if the functional response curves at 20 and o ing out 10 replications in each treatment. At this point, we 30 C represented the same models or different ones, they anticipate that although it might seem reasonable to make were compared using the extra sum-of-squares F-test with measurements at densities lower than 50, Figure 1 will show the above mentioned GraphPad software (Motulsky and egg number 50 is under the inflexion of the fitted curve, Christopoulos 2003). To discriminate between functional re- which justifies the choice of the corresponding Holling type sponse type II and type III, it is necessary to point out that at of the functional response without further measurements. both temperatures, the linear values found are positive and The containers used for parasitization were filter-paper cyl- the quadratic ones are negative, indicating type III. However, o inders (diameter 9 cm and height 5 cm) that were closed at we must highlight for values at 30 C that these include zero both sides with Petri plastic sheets. A piece of card was in their confidence interval. This needs to be interpreted with placed in each container (3 cm × 3 cm) where the E. caution since, as Juliado (2001) indicates, the parameters are kuehniella eggs were stuck using a brush and water, at each not significantly different if the confidence interval includes of the densities trialled. These were placed in rows and col- zero. umns with 2 mm separation to form the patch.

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