Responses of Delphastus Catalinae

ECOLOGY AND POPULATION BIOLOGY Responses of Delphastus catalinae (Coleoptera: Coccinellidae), a Predator of Whiteﬂies (Hemiptera: Aleyrodidae), to Relative Humidity: Oviposition, Hatch, and Immature Survival

1 2 3 ALVIN M. SIMMONS, JESUSA C. LEGASPI, AND BENJAMIN C. LEGASPI

USDAÐARS, U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, SC 29414

Ann. Entomol. Soc. Am. 101(2): 378Ð383 (2008) ABSTRACT Delphastus catalinae (Horn) (Coleoptera: Coccinellidae) is a predator of whiteßies. It is tropical in origin. Whiteßies cause problems in agriculture in both humid and arid environments. A study was conducted to determine any effects of relative humidity on oviposition, hatching, and survival of immature D. catalinae. Comparative tests were conducted among relative humidities of 25, 35, 50, and 85% and between 10 and 85% RH. All tests were conducted at 26ЊC; hence, vapor pressure deÞcits ranged from 5.04 to 30.25 mb. The study was conducted using the B-biotype sweetpotato whiteßy, Bemisia tabaci (Gennadius), as the host insect, which was reared on collard, Brassica oleracea ssp. acephala de Condolle. Egg hatch and survival to the adult stage were reduced at the lower relative humidities. At 85% RH, 99% of the eggs hatched and Ϸ90% of the beginning cohort survived to the adult stage. Conversely, Ϸ85% hatched and Ϸ60% survived to the adult stage at 25% RH, whereas 50% survived to the adult stage at 10% RH. Eggs required more time to develop at 10% RH (5.3 d) compared with 85% RH (4.1 d); a test was not set up to compare the developmental times for the larval and pupal stages. Weights of male and female D. catalinae were signiÞcantly reduced with a reduction in humidity. The results also suggest that density of immature D. catalinae, limited food supply, or both may affect survival and size of the ensuing adults. These results help in the understanding of the ecology of D. catalinae, and they indicate that extremes in ambient moisture can have an impact on the population of this predator.

KEY WORDS Bemisia tabaci, Delphastus catalinae, biological control, predator, survival

Whiteßies are important worldwide insect pests in 1997). D. catalinae is an obligate whiteßy predator (Gor- both humid and arid environments. They damage nu- don 1994). Although this beetle is native to Colombia, merous plant species in greenhouse and Þeld produc- South America, established populations can now be found tion systems by feeding and/or vectoring pathogens. in several tropical and subtropical locations, including The B-biotype sweetpotato whiteßy, Bemisia tabaci southern California, and central and southern Florida (Gennadius) (also reported as B. argentifolii Bellows (Gordon 1994, Pickett et al. 1997). Even though it prob- & Perring) and other members of the Bemisia com- ably initially arrived inadvertently on plant materials in plex, are particularly a problem in crop production. Florida, intentional releases have been made in Florida, in Because of the continued concern by the agricultural the desert southwest of the United States, and in Hawaii community and general public concern about the (Pickett et al. 1997, Hoelmer and Pickett 2003). Further- prevalent use of pesticides, there is much interest in more, dissemination of D. catalinae has been made for the use of alternative approaches, such as the use of research and biological control purposes to many inter- beneÞcial organisms, to aid in pest management in the national locations over the past several years (Hoelmer production of crops. and Pickett 2003). Because of a similar appearance, D. Several species of predators are associated with white- catalinae had previously led researchers to report it as ßies, including Delphastus catalinae (Horn) (Coleoptera: Delphastus pusillus (LeConte). The latter species occurs Coccinellidae) (Muma 1955; Hoelmer et al. 1993a, 1993b; only in the eastern United States (Gordon 1994). Gordon Legaspi et al. 1996; Nordlund and Legaspi 1996; Liu et al. (1994) provided a major revision of the genus Delphastus. He amended the original descriptions of several species, This article reports the results of research only. Mention of a described new species and updated the species distribu- proprietary product does not constitute an endorsement or recom- tion. Although D. catalinae is marketed for whiteßy con- mendation for its use by USDA. trol, there is uncertainty on the taxonomic status of the 1 Corresponding author: e-mail: [email protected]. species of Delphastus in commercial colonies. Hoelmer 2 USDAÐARS, CMAVE, Center for Biological Control, Florida A&M University, 6383 Mahan Dr., Tallahassee, FL 32308. and Pickett (2003) concluded that the species held in 3 Employed by state of Florida; contact through J.C.L. commercial insectaries are probably D. catalinae instead March 2008 SIMMONS ET AL.: HUMIDITY EFFECTS ON D. catalinae 379 of D. pusillus. They further concluded that most of the photoperiod on oviposition. Collard seedlings were published studies on the biology and behavior of D. pusillis grown in Jiffy starter pellets (Jiffy Products of Amer- on Bemisia probably pertains to D. catalinae. After obser- ica, Batavia, IL). Four collard seedlings, four- to six- vations that D. catalinae had invaded a research green- leaf stage, were placed in a cage. The cage consisted house infested with B. tabaci in Florida during the late of an 18-cm-depth by 20-cm-diameter clear plastic 1980s (Hoelmer and Pickett 2003), several studies have cylinder. The starter pellet and base of each plant was demonstrated aspects of its potential for the control of B. placed in an interlocking seal plastic bag. The bag was tabaci (Hoelmer et al. 1993a, 1993b; Heinz and Parrella zipped sealed and cotton Þber was placed around the 1994; Liu and Stansly 1999). stem of the plant to complete the seal of the bag so that Bemisia proliferates in various climates around the beetles could not crawl into the bag. Approximately globe, but only recent attention has been given to the 200Ð300 adult B. tabaci of undetermined sex were effects of climatic conditions on the populations of D. placed in each cage, and the cage was covered with catalinae. Temperature is an important limiting factor for Þne mesh screening and secured with a pair of rubber both the Bemisia host and D. catalinae. We previously bands around each cage. The cages were then held for reported on short-term critical temperature limits for the 10Ð12dat25ЊC to allow the whiteßies to establish eggs survival of adult and pupal D. catalinae (Simmons and and nymphs on the leaves. Wagner (1995) reported Legaspi 2004) and overwintering capacity in mild win- that the egg of B-biotype B. tabaci hatches in 7.1 d at ters of coastal South Carolina and northern Florida (Sim- 24ЊC on cotton. After the whiteßy incubation period, mons and Legaspi 2007). Temperatures below 5ЊC for each whiteßy-infested plant was placed inside a 24 h had a considerable detrimental impact on survival of 480-ml cylindrical paper carton with Þne mesh screen- D. catalinae (Simmons and Legaspi 2004). Likewise, cli- ing secured to the top, and six adult female D. catalinae mate can dramatically affect the population and distri- were added to each cage. Ten of these caged plants bution of its Bemisia host (Gerling 1984, Simmons and were placed into one of three photoperiod regimes Elsey 1995, Simmons 1998). Coastal South Carolina is the (24:0, 12:12, and 0:24 [L:D] h) in environmental cham- most northern range of eastern North America where bers at 26ЊC and 85% RH. Lighting in the chambers was feral populations of the B-biotype B. tabaci survive by ßorescent bulbs oriented vertically along two op- throughout the winter, although the population is much posite walls. After 24 h, the number of C. catalinae eggs reduced compared with warmer months (Simmons and deposited on the leaves was determined for each plant Elsey 1995). Severely depressed populations of D. catali- for each photoperiod regime. The experiment was nae can survive such mild winters where the low tem- repeated Þve times by using different chambers for peratures are commonly above 0ЊC (Simmons and Le- each photoperiod test. gaspi 2007). Humidity can affect developmental rate and Oviposition and Humidity. An experiment was con- survival of eggs and immatures of some arthropods, ducted to test for any inßuence of humidity on ovi- including species of Acari, Coleoptera, Diptera, position by D. catalinae. Two relative humidity ex- Hemiptera, and Orthoptera (Chapman 1969, Ferro and tremes, 10 Ϯ 6% and 85 Ϯ 5% RH, were tested using Chapman 1979, Martinat and Allen 1987). However, environmental chambers (model I-36VL, Percival, there have been no published reports on the effect of Perry, IA) maintained at 26ЊC and a photoperiod of relative humidity on populations of D. catalinae. 16:8 (L:D) h. Vapor pressure deÞcit was 30.04 and 5.04 Knowledge of the ecology of whiteßy predators will mb for the 10 and 85% RH treatments, respectively. facilitate their role as a pest management component. Humidity for the 10% treatment was maintained with The purpose of this study was to determine any in- a built-in IAT-50 U in the chamber. Humidity for the ßuence of relative humidity on oviposition, hatch, egg 85% treatment was provided by an open container of developmental rate, and survival of immature D. water in the chamber. Collard plants were infested catalinae on B. tabaci as a host. In addition, an exper- with whiteßies as described above. Six adult female iment was conducted to determine any inßuence of beetles were then added to each 480-ml paper carton photoperiod on oviposition by D. catalinae. cage as described above. Ten cages were set up per treatment chamber. After 24 h, the number of eggs deposited were counted and recorded. The experi- Materials and Methods ment was repeated eight times. Oviposition and Photoperiod. Insects used in all ex- Survival from Oviposition to Adult Emergence at periments were from greenhouse colonies maintained at Four Relative Humidities. A laboratory study was set the USDAÐARS, U.S. Vegetable Laboratory, Charleston, up to test D. catalinae in four separate environmental SC. The whiteßies, B-biotype B. tabaci, had been reared chambers (Percival model I-36VL) maintained at 26 Ϯ on assorted vegetable crops since 1992 (Simmons 1994). 1ЊC and a photoperiod of 16:8 (L:D) h. The chambers Adult coccinellids (D. catalinae) were purchased com- were maintained at 25, 35, 50, or 85% RH. A portable mercially in 1999 and released to help suppress whiteßies dehumidiÞer connected to a humidistat controller in a research greenhouse, and they have persisted on B. (model RHC, Green Air Products, Gresham, OR) in tabaci since the original release. Voucher specimens of D. conjunction with an open container of water was used catalinae from the colony were deposited at the Division to maintain the humidity in each chamber. Collard of Plant Industry, Gainesville, FL. seedlings were set up in interlocking seal plastic bags To assist with the methods for the humidity tests, an and infested with whiteßy eggs and nymphs as de- experiment was conducted to test for any inßuence of scribed above. The bags were to help limit ambient 380 ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 101, no. 2 moisture and to prolong moisture on the pellets for the Table 1. Mean number of eggs deposited when D. catalinae was plants. After the whiteßy incubation period, each held under three photoregimes for 24 h at 26°C bagged plant was transferred to a 480-ml cylindrical No. eggs/six females/24 h paper carton with Þne mesh screening secured to the Photoregime n Mean Ϯ Upper leaf Range top. Six adult female D. catalinae were collected from SEM surface the greenhouse colony and placed in each cage. Free water was not provided for the beetles. Cages with 24:0 50 22.7 Ϯ 2.8a 3Ð66 0.5 Ϯ 0.16b 12:12 50 22.1 Ϯ 2.0a 4Ð49 0.8 Ϯ 0.18b beetles were placed in each of the four aforemen- 0:24 50 22.6 Ϯ 2.6a 0Ð69 1.4 Ϯ 0.30a tioned relative humidity chambers. Within 18Ð26 h, the adult beetles were removed from the cages. With Means in columns followed by the same letters are not signiÞcantly the aid of a microscope, all eggs that were deposited different (P Ͼ 0.05) according to StudentÐNewmanÐKeuls test. on the leaves were circled with a red Þne-point per- manent marker (Sharpie, Series No. 30000, Stanford eggs was placed in one of the 20-cm-diameter cylinder Corporation, Bellwood, IL) to aid in the relocation of clear cages and laid on its side so that the leaf with eggs the eggs. The number of eggs per plant was recorded. was turned upward. Four plants were set up for each Four plants with beetle eggs were placed in each of the treatment. Daily observations were made on egg clear aforementioned 20-cm-diameter cylinder cages. hatch, and the number of days to hatch was recorded During the experiment, water was added as needed for each egg. Eggs that did not hatch were not in- within the plastic bag, and it was resealed. Three cages cluded in the analyses. The experiment was repeated were set up per chamber for a total of 12 plants per three times for each treatment. trial. The cages were returned to the same relative Data Analysis. Data were analyzed using SAS (SAS humidity chamber in which oviposition had taken Institute 2002), and signiÞcance was determined at place. The plants were observed 8 d after the ovipo- P Ͻ 0.05. Percentages were transformed using arcsine sition period, and the numbers of eggs that hatched transformation before the analysis, but the results are were recorded for each plant. Liu (2005) reported that presented on back-transformed data. SigniÞcantly dif- it takes4dforD. catalinae to hatch at 26ЊC and 55% ferent means were separated using the StudentÐNew- RH; thus, any unhatched eggs found on day 8 were manÐKeuls test. Correlation relationships were tested assumed not to be able to hatch. To augment the diet between percentage of egg hatch and percentage of of immature whiteßies for the beetle larvae, Ϸ200Ð300 relative humidity. adult B. tabaci were added to each cage and the cages were returned to the humidity treatment from which they had been previously held. From 24Ð36 h after Results and Discussion emergence, the gender and weight of each adult bee- Oviposition as Inﬂuenced by Photoperiod and Hu- tle were determined and recorded. The experiment midity. There were no signiÞcant differences (F ϭ was repeated eight times. 0.39, P Ͼ 0.68) in the total number of D. catalinae eggs Survival from Oviposition to Adult Emergence at deposited at any of three photoperiods (Table 1). No Two Relative Humidities. An experiment was con- signiÞcant chamber effect was detected on number of ducted on survival from oviposition to the adult stage eggs deposited. An overall average of 23 eggs per six in a comparison between beetles held at 10 and 85% females and a range of 0Ð69 eggs were deposited RH. The test was set up using the same materials and within 24 h by sets of six females. Darkness increased methods as for the previous test with four relative the number of eggs that was deposited on the upper humidities, except that the number of eggs was lim- surface of the leaf, although only a few (4%) of the ited. Six eggs remained on the leaves of each plant overall eggs were deposited on the upper surface (Ta- after all other eggs were removed within 24 h of ble 1). In the other experiments herein, we similarly oviposition. Data on hatch, survival, and weight were found most of the eggs on the lower leaf surface. collected as in the aforementioned test. The experi- Humidity had an effect on the rate of oviposition for ment was repeated seven times. A total of 168 eggs D. catalinae adult females held for 24 h at 10 and 85% were tested in each treatment of 10 and 85% RH. RH. The latter resulted in a statistically greater num- An additional test was set up to test for any effect ber of eggs (F ϭ 4.01, P Ͻ 0.05), but the magnitude was of humidity on egg developmental rate. Treatments of not large (Table 2). There were 0Ð67 eggs deposited 10 and 85% RH under the above-described conditions were used. Eggs were obtained by allowing adult female D. catalinae to oviposit on collard plants set up in Table 2. Mean number of eggs deposited at two relative hu- plastic bags as described above, and all plants were midities for D. catalinae held in the laboratory at 26°C held at 85% RH to standardize the condition during Min. no. Max no. the ovipositional period. Six beetle eggs were gently % relative Mean Ϯ % eggs n eggs/six eggs/six humidity SEM eggs deposited removed one at a time, by using a probe, and they were females females placed on the lower surface of a collard leaf infested with whiteßy eggs and nymphs as described above. 10 70 16.8 Ϯ 1.4b 0 54 43.7 Ϯ 3.7b 85 70 20.6 Ϯ 1.8a 0 67 56.3 Ϯ 5.1a The six beetle eggs were placed within an area of Ϸ3 cm in diameter, which was marked with a red pen to Means in columns followed by different letters are signiÞcantly facilitate the relocation of the eggs. One plant with different (P Ͻ 0.05) according to StudentÐNewmanÐKeuls test. March 2008 SIMMONS ET AL.: HUMIDITY EFFECTS ON D. catalinae 381

100 Table 3. Mean percentages of hatch and survival to the adult 90 Egg Hatch a stage for D. catalinae held at a high and a low relative humidity in the laboratory with eggs limited to six per plant (26°C) 80 b ab 70 b % relative Mean Ϯ SEM Mean Ϯ SEM % 60 na 50 humidity % hatch adult emergence 40 10 28 84.7 Ϯ 1.95b 50.1 Ϯ 3.4b 30 85 28 99.3 Ϯ 0.37a 93.5 Ϯ 2.0a 20 10 Means in columns followed by different letters are signiÞcantly 0 different (P Ͻ 0.05) according to StudentÐNewmanÐKeuls test. 100 a For each treatment, 168 eggs were tested. 90 Egg to Adult 80 a 70 ab Similar to egg hatch, overall survival to the adult

% Survival 60 bc stage was reduced with a decrease in humidity (Fig. 50 c 1). In the experiment with four treatments, 86.5% of 40 the immatures survived to the adult stage at 85% RH, 30 whereas 58.5% survived to the adult stage at 25% RH 20 (Fig. 1). Survival (93.5%; Table 3) to the adult stage 10 tended to have been more favorable at 85% RH when 0 egg density was limited to six D. catalinae per plant 25 35 50 85 compared with when egg density was not limited. We % Relative Humidity suspect that beetle density may have had some inßu- ence on survival by limiting the food supply. Survi- Fig. 1. Survival of D. catalinae at four relative humidity vorships for immatures in the tests at 85% RH are treatments when held in the laboratory from the time of similar to what was reported (88% survival from egg to oviposition until adult emergence on B. tabaci-infested col- adult at 26ЊC) by Liu (2005) whom studied the insects lard plants (26ЊC); Means followed by different letters are on leaf disks in petri dishes with ambient condition signiÞcantly different (P Ͻ 0.05) according to StudentÐNew- outside of the dishes at 55% RH. At 10% RH, survival manÐKeuls test. from egg hatch to adult emergence was 50% (Table 3), which seems to be consistent with the adverse impact for a given cage of six adult D. catalinae within 24 h. of humidity as was observed in the experiment with To avoid age bias, random female beetles from the 25% RH (58.5% survival; Fig. 1). colony population were used in the experiments. They Apparently, too little moisture may be deleterious. In represented samples of egg production by the colony, the lepidopteran Heterocampa guttivitta (Walker), hu- and their ages presumably ranged from recently midity affected survival but not developmental rate of emerged to old age. The preoviposition period for this the eggs (Martinat and Allen 1987). In our study, data on species averages 5 d (Liu 2005), and viable eggs can be developmental rate for egg hatch indicate that more time deposited for the remainder of their life (Simmons and (1.2 d) is needed for egg hatch at low humidity compared Legaspi 2007). In research on a tropical leafhopper with high humidity (Table 4). Because the eggs were species, Alyokhin et al. (2004) concluded that there exposed to the separate treatments after the oviposition was no effect of humidity on oviposition when they period, the full impact of low humidity on rate of egg studied Þeld sites differing in annual precipitation development may be underdetermined herein. The 4-d (1,700Ð3,000 mm). Apparently, ambient moisture is a duration of the egg stage under 85% RH is the same as minor factor in affecting the oviposition behavior for reported by Liu (2005) for insects in petri dishes that D. catalinae. were held at 55% RH and at the same temperature as in Survival from Oviposition to Adult Emergence. Egg our study. In the experiment where survival was fol- hatch by D. catalinae signiÞcantly decreased as rela- lowed to the adult stage, unhatched eggs of different tive humidity was changed from 85 to 25% (Fig. 1). Similarly, egg hatch was higher for the high humidity (85%) treatment when only two treatments (includ- Table 4. Mean number of days to develop from oviposition to ing 10% RH) were tested (Table 3). Egg hatch ranged eclosion for D. catalinae held at high and low relative humidity from 84.7 to 99.3% in the experiment among the four treatments (26°C) relative humidity treatments (Fig. 1), and in the ex- Mean Ϯ SEM % relative periment between the two relative humidity treat- na no. days to humidity ments (Table 3). Egg hatch was moderately correlated eclosion ϭ Ͻ (r 0.40, P 0.001) with relative humidity in the 10 33 5.3 Ϯ 0.08b experiment with the four treatments (Fig. 1). Hatch 85 52 4.1 Ϯ 0.06a performance (Ϸ85%) was comparable for the lowest humidity treatments (10 and 25% RH) in two exper- Means followed by different letters are signiÞcantly different (P Ͻ iments, and hatch performance (Ϸ100%) was compa- 0.05) according to StudentÐNewmanÐKeuls test. a Unhatched or lost eggs were not included in the analyses. The rable at the highest humidity treatments (85% RH) in eggs were transferred from one collard leaf to a new leaf; 87 and 53% the same two experiments (Fig. 1; Table 3). hatched at 85 and 10% RH, respectively. 382 ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 101, no. 2

Table 5. Mean weight of adult D. catalinae after the immature orum (Westwood), as a host, Lucas et al. (2004) reported developed at four different relative humidities in the laboratory an average weight of 0.53 mg for D. catalinae. They did (26°C) not provide data on the weight by sex. Weight can be used as an index of size, and size may be an indication of % relative Mean Ϯ SEM wt (mg) n humidity Males Females Average Þtness of an organism. However, no data were collected on the reproductive and survival of the adults in response 25 318 0.336 Ϯ 0.008b 0.407 Ϯ 0.011b 0.369 Ϯ 0.007c to different relative humidities. The data do not deÞne 35 336 0.380 Ϯ 0.009a 0.426 Ϯ 0.009ab 0.403 Ϯ 0.006ab 50 440 0.375 Ϯ 0.007a 0.411 Ϯ 0.007ab 0.391 Ϯ 0.005b the speciÞc optimal relative humidity for D. catalinae, but 85 506 0.390 Ϯ 0.008a 0.440 Ϯ 0.008a 0.414 Ϯ 0.006a they indicate that it would be Ͼ50% RH. Nevertheless, very high humidity may provide adverse pathological Means in columns followed by different letters are signiÞcantly conditions. At 85%, there was a high incidence of mold Ͻ different (P 0.05) according to StudentÐNewmanÐKeuls test. and mildew on the leaves, which was not noticeable at low relative humidity. Although there were adult white- developmental stages were noticed. Once the eggs ßies that continued to oviposit on the leaves throughout hatched, the larvae had access to moisture by feeding on the experiment, we suspect that food may have been the whiteßy host and/or honeydew. Liu and Stansly limited at times in part due to the presence of the mold (1999) observed that some D. catalinae larvae fed on and mildew. Moreover, because of the relatively high honeydew and dew drops even when abundant white- number of D. catalinae larvae on leaves (a maximum of ßies were present. Adults and larvae of this coccinellid 42, but generally between 15 and 20 eggs per plant) in the species feed on a liquid diet. Based on where pupae were experiment with multiple humidities, insufÞcient diet found, some larvae moved among leaves and plants may have been related to the general small size com- within a cage. Similar to what we observed on plants in pared with the experiment with six eggs per plant. In the greenhouse colony, in this study, some larvae pu- other laboratory observations, we have rarely observed pated on the stem of the plant and in some cases on the cannibalism by the larvae. We do not know whether container (i.e., plastic bag) holding the roots of the cannibalism may have been a factor on survival in either plants. However, pupae and pupa cases were not ob- experiment, but such behavior was not observed in this served on the cages. The data suggest that at extremely study. Nevertheless, in the experiment with low density, low ambient moisture, the ability of D. catalinae larvae to the beginning cohorts were equal. The larvae tend to replenish moisture in its body may have been hampered, complete feeding on a host once they start feeding, but leading to an increase in mortality. We observed that prey handling time tends to increase under food depri- some died during the egg stage, larval stage, during eclo- vation (Liu and Stansly 1999). sion, and shortly after exiting the pupal case. In conclusion, results from this study indicate that Adult Weight. In every test within a given humidity populations of D. catalinae can be affected by the treatment, females weighed signiÞcantly more than amount of humidity in the environment. Vapor pres- males. Overall weights of both males and females were sure deÞcit, which expresses moisture status indepen- generally reduced with an increase in percentage of dent of temperature, is biologically more meaningful relative humidity (Tables 5 and 6). In the test with four than relative humidity (Ferro and Chapman 1979). humidity treatments, weights for the highest (0.414 mg) Ambient moisture was not constant in the study herein and the lowest (0.369 mg) percentage of relative hu- because temperature was held constant. Vapor pres- midity differed signiÞcantly (Fϭ9.16, PϽ0.05), whereas sure deÞcits in this study ranged from 30.25 mb (10% the weights of adults that developed at 35 and 50% were RH) to 5.04 mb (85% RH). A failure of D. catalinae to statistically the same (Table 5). Using a sample of 100 control B. tabaci in the Þeld on cotton, Gossypium beetles of each sex from the greenhouse colony, adult D. hirsutum L. (Heinz and Parrella 1994) may be only catalinae males and females had mean weights of 0.500 Ϯ partly related to the effect of humidity on the popu- 0.015 and 0.564 Ϯ 0.021 mg, respectively. These sizes lation. The role of temperature is very important on were similar to the experiment with limited D. catalinae the biology and ecology of D. catalinae (Simmons and egg density at 85% RH. In that experiment, the average Legaspi 2004, Simmons and Legaspi 2007, Legaspi et al. weight for males and females were 0.490 and 0.567 mg, 2008). As such, increased or decreased temperatures respectively (Table 6). In a study under 24ЊC and 70% can affect biological parameters of this predator, but RH with the greenhouse whiteßy, Trialeurodes vaporari- there has not been a report on a study of any inter- action of temperature and humidity. The intensity and duration of exposure to adverse factors can limit the Table 6. Mean weight of adult D. catalinae after the immature survival of insects. During a typical day within either developed at a high and a low relative humidity with eggs limited to an arid environment such as the U.S. southwest desert six per plant in the laboratory (26°C) or a humid environment such as the southeastern United States, relative humidity may not vary exces- % relative Mean wt (mg) Ϯ SEM n humidity Males Females Average sively between the low and high extremes. Similarly, vapor pressure deÞcit within a closed greenhouse sys- 10 339 0.440 Ϯ 0.008b 0.489 Ϯ 0.007b 0.467 Ϯ 0.006b tem generally does not vary excessively, and it is usu- 85 603 0.490 Ϯ 0.005a 0.567 Ϯ 0.006a 0.529 Ϯ 0.004a ally under humidity conditions that are favorable to Means in columns followed by different letters are signiÞcantly the population of D. catalinae. The results of this study different (P Ͻ 0.05) according to StudentÐNewmanÐKeuls test. support that although D. catalinae can exist in a wide March 2008 SIMMONS ET AL.: HUMIDITY EFFECTS ON D. catalinae 383 range of humidities, low ambient moisture can have a Liu, T.-X., and P. A. Stansly. 1999. Searching and feeding negative impact on its population dynamics. behavior of Nephaspis oculatus and Delphastus catalinae (Coleoptera: Coccinellidae), predators of Bemisia argentifolii (Homoptera: Aleyrodidae). Environ. Entomol. 28: Acknowledgments 901Ð906. Liu, T.-X., P. A. Stansly, K. A. Hoelmer, and L. S. Osborne. 1997. Appreciation is given to Bradford Peck, Courtney Life history of Naphaspis oculatus (Coleoptera: Coccinelli- Hawkins, Kristie Fenn, and Peter Washburn for technical dae), a predator of Bemisia argentifolii (Homoptera: Aley- assistance and to D. Michael Jackson and Gloria McCutcheon rodidae). Ann. Entomol. Soc. 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