STORED-PRODUCT Population Growth and Development of the Psocid Liposcelis brunnea (Psocoptera: Liposcelididae) at Constant Temperatures and Relative Humidities 1 G. P. OPIT AND J. E. THRONE USDAÐARS, Grain Marketing and Production Research Center, 1515 College Ave., Manhattan, KS 66502-2736 J. Econ. Entomol. 102(3): 1360Ð1368 (2009) ABSTRACT We studied the effects of temperature and relative humidity on population growth and development of the psocid Liposcelis brunnea Motschulsky. L. brunnea did not survive at 43% RH, but populations increased from 22.5 to 32.5ЊC and 55Ð75% RH. Interestingly, we found population growth was higher at 63% RH than at 75% RH, and the greatest population growth was recorded at 32.5ЊC and 63% RH. At 35ЊC, L. brunnea nymphal survivorship was 33%, and populations declined or barely grew. L. brunnea males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 13, 82, and 5%, respectively. Female L. brunnea have three to Þve instars, and the percentages of females with three, four, and Þve instars were 18, 78, and 4%, respectively. The life cycle was shorter for males than females. We developed temperature-dependent development equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages and nymphal survivorship. The ability of L. brunnea to multiply rather rapidly at 55% RH may allow it to thrive under conditions of low relative humidity where other Liposcelis species may not. These data give us a better understanding of L. brunnea population dynamics and can be used to help develop effective management strategies for this psocid. KEY WORDS stored products, development rates, life history, grain Psocids of the genus Liposcelis increasingly pose a rugosa Badonnel in Canada, but Lienhard (1990) re- threat to stored products (Rees 1998). Until recently, ported that these were actually L. bostrychophila that psocids were regarded only as nuisance pests feeding had been misidentiÞed as L. rugosa. on molds (Kucˇerova´ 2002). However, weight losses We conducted studies in 2006 to determine which caused by germ and endosperm consumption by pso- species of psocids were present in wheat stored in steel cids (McFarlane 1982, Kucˇerova´ 2002), frequent fail- bins, a feed mill, and an elevator in Manhattan, KS ure of standard practices of protection and disinfes- (unpublished data). We found all seven species listed tation to control psocids (Wang et al. 1999a, Beckett above that had previously been reported in the United and Morton 2003, Nayak et al. 2003, Nayak and Daglish States. There have been studies on the biology of L. 2007), and the fact that commodities infested by pso- bostrychophila (Rees and Walker 1990; Turner 1994; cids can be rejected for export (Kucˇerova´ 2002, Nayak Wang et al. 1999b, 2000), L. decolor (Tang et al. 2008), 2006) have led to the recognition of psocids as serious L. entomophila (Rees and Walker 1990; Leong and Ho pests. Psocid species known to infest grain in North 1995; Wang et al. 1998; Mashaya 1999, 2001), L. paeta America (Sinha 1988, Mockford 1993, Lienhard and (Rees and Walker 1990), and L. reticulatus (Opit and Smithers 2002) are Lepinotus reticulatus Enderlein Throne 2008). However, there are no published stud- (Psocoptera: Trogiidae), Liposcelis bostrychophila Ba- donnel (Psocoptera: Liposcelididae), Liposcelis brun- ies on the biology of L. corrodens or L. brunnea. De- nea Motschulsky, Liposcelis corrodens (Heymons), Li- velopment of an effective management program for poscelis decolor (Pearman), Liposcelis entomophila any pest is dependent on having sound knowledge of (Enderlein), and Liposcelis paeta Pearman. Sinha its ecology. Given the lack of information on ecology (1988) had indicated that he had found Liposcelis of L. brunnea, we initiated studies on population growth and development of L. brunnea to provide an Mention of trade names or commercial products in this publication experimental basis for developing pest management is solely for the purpose of providing speciÞc information and does not strategies for this pest. Our objectives were to deter- imply recommendation or endorsement by Oklahoma State Univer- mine the effects of constant temperature and relative sity or the U.S. Department of Agriculture. humidity on population growth of L. brunnea and to 1 Corresponding author: Department of Entomology and Plant Pa- thology, Oklahoma State University, Stillwater, OK 74078-3033 (e- quantify the effects of temperature on development of mail: [email protected]). L. brunnea. June 2009 OPIT AND THRONE:POPULATION GROWTH AND DEVELOPMENT OF L. brunnea 1361 Materials and Methods Ϸ1Ð2 wk old (based on preliminary work we had done that indicated that development of females from egg Insects. Cultures used in the study were started with to adult took Ϸ31dat30ЊC). insects collected during the summer of 2006 in a grain Five 1- to 2-wk-old adult females were added to elevator at the Grain Marketing and Production Re- each of the 120 vials containing equilibrated diet, search Center in Manhattan, KS. Voucher specimens which were incubated at each of the 24 temperature- of 50 female L. brunnea preserved in alcohol that were relative humidity combinations. Six incubators were used in this study were deposited in the Kansas State set at temperatures of 22.5, 25.0, 27.5, 30.0, 32.5, and University Museum of Entomological and Prairie Ar- 35.0ЊC, and into each incubator were placed four plas- thropod Research under lot 203. Psocids were reared tic boxes (20 by 12.5 by 10 cm high) containing sat- on a mixture of 93% cracked hard red winter wheat, 5% urated solutions of K2CO3, NaBr, NaNO2, and NaCl. wheat germ, and 2% rice krispies (Kellogg Company, Five vials containing diet equilibrated at room tem- Battle Creek, MI) (wt:wt; referred to as psocid diet perature and each relative humidity were randomly below) in 0.473-liter glass canning jars covered with assigned to the corresponding relative humidity box in mite-proof lids (Opit and Throne 2008), and cultures Њ each incubator. Four positions were established in were maintained at 30 C and 75% RH. each incubator for the boxes to occupy. Every 7 d, the Effects of Temperature and Relative Humidity on boxes in each incubator were shufßed so that each box Population Growth. We determined the effects of spent a total of at least7dineach position during the temperature and relative humidity on the increase in course of the experiment to counteract any temper- number of psocids over a 30-d period at six temper- ature variability that may have existed in the incuba- Њ atures (22.5, 25.0, 27.5, 30.0, 32.5, and 35.0 C) and four tors. During shufßing, the boxes were also checked to relative humidities (43, 55, 63, and 75%)Ñi.e., 24 tem- ensure that the salt solutions were still saturated. En- perature/relative humidity combinations. The top vironmental conditions in each incubator were mon- third of the inner surface of 120 vials was coated with itored using a temperature and relative humidity sen- Fluon (polytetraßuoroethylene; Northern Products, sor (HOBO U12; Onset Computer, Bourne, MA). Live Woonsocket, RI) to prevent psocids from escaping, insects in each vial were counted after 30 d by spread- and5gofcracked hard red winter wheat (Triticum ing a portion of the contents of a vial on a 9-cm petri aestivum L.) were placed in each vial. A screen (U.S. dish, which had a coat of Fluon on the walls, and #40 mesh) was placed in the snap-cap lid to allow air removing motile L. brunnea using a moist brush under movement. Vials were randomly placed in each of four a stereomicroscope (Wild M5A; Wild Heerbrugg, plastic boxes (40 by 27.5 by 16 cm high) containing Heerbrugg, Switzerland). saturated solutions of K2CO3, NaBr, NaNO2, and NaCl The experiment had three replications over time, below perforated false ßoors to maintain relative hu- and the experimental design was a randomized com- midities of 43, 55, 63, and 75% (Greenspan 1977), plete block (RCBD) with subsampling. Five vials were respectively, and the cracked wheat in the vials was placed in each plastic box (20 by 12.5 by 10 cm high) equilibrated for moisture content at room tempera- during replications 1 and 3, and four were placed in ture for 4 wk. each box in replication 2. All statistical procedures One- to 2-wk-old female L. brunnea for the exper- were accomplished using Statistical Analysis System iment were obtained by placing1gofcolored psocid software (SAS Institute 2001). PROC MIXED was diet (Opit and Throne 2008), 10 particles of cracked used for analysis of variance (ANOVA) to determine wheat, and 30 adult female psocids of unknown age the effects of temperature and relative humidity on from our culture in each of eighty 35-mm-diameter the numbers of psocids in the vials, which were trans- petri dishes (Greiner Bio-One, Kaysville, UT), which formed using the square-root transformation to stabi- had a coat of Fluon on the walls to prevent psocids lize variances before analysis. Untransformed means from escaping. Colored diet was used because we and SEs are reported to simplify interpretation. We found that L. brunnea prefer laying eggs on and among used a least signiÞcant difference (LSD) test to de- diet particles, and colored diet makes it easier to see termine differences among mean numbers of psocids eggs and, therefore, make an assessment of whether produced at different temperatures and relative hu- sufÞcient numbers of eggs are being laid for the ex- midities, despite the quantitative independent vari- periment. The petri dishes were placed on false ßoors ables, because we were not able to quantify the rela- in three Rubbermaid plastic boxes (30 by 23 by 9 cm tionship using a biologically meaningful equation high) that contained saturated NaCl solution.