Biological Control 42 (2007) 186–195 www.elsevier.com/locate/ybcon Influence of diet on long-term cold storage of the predator Podisus maculiventris (Say) (Heteroptera: Pentatomidae) q T.A. Coudron a,*, M.R. Ellersieck b, K.S. Shelby a a Biological Control of Insects Research Laboratory, USDA-Agriculture Research Service, 1503 S. Providence Road, Columbia, MO 65203-3535, USA b Agricultural Experiment Station Statisticians, University of Missouri, Columbia, MO 65211, USA Received 26 December 2006; accepted 23 April 2007 Available online 29 April 2007 Abstract Long-term storage could aid in the cost-effective mass production of beneficial insects. Pre-conditioning, insect developmental stage and environmental conditions should be considered when selecting storage conditions in order to obtain the highest performance after storage. We evaluated the influence of nutrient quality on the response of eggs, nymphs and adults of Podisus maculiventris when exposed to two temperatures most likely to be used for long-term storage. Natural prey-fed insects were compared to artificial diet-fed insects. The results of our study showed that eggs survived storage at 10 °C better than 4 °C, and that eggs from diet-fed insects survived storage at 10 °C significantly better than eggs from prey-fed insects. Nymphal survival of cold storage treatment was slightly higher than for eggs, with a similar pattern of response to temperature, nutrient quality and time of storage. However, of the three developmental stages tested, the best survival was obtained with adults. Similar to eggs and nymphs, adults survival was higher at 10 °C. However, different from eggs and nymphs was that the prey-fed adults survived better than diet-fed adults. Our results show that prey-fed adults were able to withstand cold storage at 10 °C for 4 weeks with very little loss of survival, fecundity or viability of eggs oviposited by those adults. Longer periods of storage resulted in a decline in survival, fecundity and egg viability and that decline was greatest at 4 °C. For the longer intervals of storage at 10 °C, egg viability was highest for eggs from diet-fed adults. Collectively, these results demonstrate an influence of nutrient quality on the response to cold storage at different developmental stages, and that an optimal food source for continuous rearing is not necessarily an optimal food source for cold storage. Published by Elsevier Inc. Keywords: Podisus maculiventris; Cold storage; Diet; Nutrient quality; Survival; Fecundity 1. Introduction respond to undulating and unpredictable demands. Cold storage may be a useful technique to enable insectaries One of the primary obstacles to the use of insect natural and researchers to store insects for extended periods rather enemies for biological control is the difficulty and expense than to continuously rear a colony during those times when of rearing these insects in sufficient numbers and quality for the colony is not in use. Additionally, cold-storage could fluctuating markets. More efficient storage methods would assist in accumulating sufficient numbers of insects for substantially improve the options available to insectaries to innundative releases, or minimizing costs of retaining a col- ony between inoculative releases, off-season demands and q Mention of trade names or commercial products in this publication is between research studies. Tolerance to cold may also be solely for the purpose of providing specific information and does not considered a desirable attribute for shipment and for fitness imply recommendation or endorsement by the US Department of when used in early or late season releases. Agriculture. All programs and services of the US Department of The response of insects to cold temperatures has Agriculture are offered on a nondiscriminatory basis without regard to received considerable interest, with the majority of studies race, color, national origin, religion, sex, age, marital status, or handicap. * Corresponding author. Fax: +1 573 875 4261. focusing on diapause. However, the role of nutrient quality E-mail address: [email protected] (T.A. Coudron). in diapause is not well understood (Ruberson et al., 1998). 1049-9644/$ - see front matter Published by Elsevier Inc. doi:10.1016/j.biocontrol.2007.04.014 T.A. Coudron et al. / Biological Control 42 (2007) 186–195 187 The intentional cooling of insects for the purpose of stor- chamber. The prey-fed colony used in this study had been age has focused mostly on beneficial insects with some of maintained for ca. 80 generations on excess quantities of the earlier studies investigating parasitoids (Flanders, coddled fourth instar larvae of Trichoplusia ni (Hu¨bner) 1938; DeBach, 1943). More recently two studies have doc- (Coudron et al., 2000) and the diet-fed colony had been umented that host quality influences the response of bene- maintained for ca. 10 generations on excess quantities of ficial insects subjected to cold temperatures. In one study a zoophytogenous artificial diet (Coudron et al., 2002). involving the predatory pentatomid, Podisus maculiventris These two food sources were used for this study to provide (Say) (Heteroptera: Pentatomidae) it was reported that an optimal nutrition (prey-fed) that has been previously suboptimal food increased the number of individuals that used to maintain a continuous colony of P. maculiventris entered a putative diapause condition (Goryshin et al., for more than 150 generations and suboptimal nutrition 1988). In another study, the presence of cryoprotectants (diet-fed) that has been previously used to maintain a con- in the host were credited with improving the cold hardiness tinuous colony of P. maculiventris for more than 100 gen- in larvae of the fly pupal parasitoid, Nasonia vitripennis erations (Coudron et al., 2002, 2006; Yocum et al., 2006). (Walker) (Hymenoptera: Pteromalidae) (Rivers et al., Eggs, nymphs and adults from the prey-fed and diet-fed 2000). colonies that were used in each cold storage treatment were The spined soldier bug, P. maculiventris, is a polypha- cohorts (Birch, 1948; Wittmeyer et al., 2001) collected as gous predator of many agricultural pests and is native to eggs from control adult females that ranged in age from North America (McPherson, 1980, 1982). P. maculiventris 6 to 20 days old. has often been a preferred predator for research, sale and use because of its high reproductive capacity and its ability 2.2. Temperature treatments to be reared on artificial diets. Parallel with interests in storing insects has been a long-established interest in the Eggs, nymphs and adults were subjected to cold storage use of artificial diets to reduce the production costs and in continuous darkness and 75% RH within incubators set maintain stable colonies of insects. As with most beneficial at either 4 °Cor10°C. These temperatures prevent embry- insects, current methods for mass rearing P. maculiventris onic development in eggs that are <1 day post oviposition involve rearing on a natural host. However, several artifi- (Goryshin and Tuganova, 1989; De Clercq and Degheele, cial diets have been tested for rearing P. maculiventris, cul- 1992). A RH of >75% has been shown to be critical for sur- minating with a zoophytogenous diet that has proven to be vival. Pre-conditioning for the induction of diapause was cost-effect and has been successfully used to maintain a col- not attempted because this had previously been shown ony for more than 200 consecutive generations. The zoo- not to occur for P. maculiventris (Couturier, 1938; Vlasova phytogenous diet has not been fully optimized for et al., 1980; De Clercq and Degheele, 1993). Stored insects continuous rearing and at its original formulation resulted were provided water absorbed on a dental wick but were in an increase in developmental time and a decrease in not provided with prey or diet. Unless otherwise stated, fecundity (Coudron et al., 2002). Other possible effects random samples (Snedecor and Cochran, 1989) of three were indicated by altered gene expression patterns (Yocum replicates of 20 individuals were removed from each treat- et al., 2006; Coudron et al., 2006). ment at designated time points over a 10 week period for In the present study, the potential of nutrient quality on observation and recording. Samples removed for observa- responses of P. maculiventris to storage at two reduced tions were not returned to the study. temperatures were evaluated by measuring survival, fecun- Eggs from prey-fed and diet-fed females were collected dity and egg viability of P. maculiventris reared on larvae of at ca. 1 day post oviposition before being subjected to cold Trichoplusia ni or an artificial diet. In addition to Proc storage treatment. Three groups of 20 eggs were randomly Genmod analyses, the use of odds ratios analyses, i.e., an removed from cold storage treatment at the designated extension of a general linear model analysis, linked to a time points and subsequently held at 26 °C, 75% RH and logit (nonlinear) transformation to provide a good linear observed for hatch over a 7 day period. fit assigning a binomial distribution, enabled the compari- Prey-fed and diet-fed nymphs were subjected to cold son of uneven data sets that resulted from the extensive dif- storage treatment as newly ecdysed third instar nymphs, ferences of each developmental stage in response to the collected within 4–8 h of molting. Survival was recorded treatments. in two groups of 10 nymphs that were randomly removed from cold storage treatment at the designated time points 2. Materials and methods and observed for survival over a 7 day period. Male and female adults 2 days post adult eclosion were 2.1. Insect colonies and diet separated and subjected to cold storage treatment. Survival was recorded in two groups of 10 males and females. Sub- The P. maculiventris colony originated from adults col- sequently, adults removed from cold storage treatment lected in alfalfa in Boone County, Missouri in the summer were held at 26 °C, 16 L:8D photoperiod, and 75% RH of 2000 and subsequently maintained continuously at and survival was recorded 24 h after removal from the cold 26 °C, 16L:8D photoperiod, and 75% RH in a walk-in storage.