Benjamin C. Legaspi

Life table analysis for Cactoblastis cactorum immatures and female adults under five constant temperatures : Implications for pest management

Abstract The cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), was reported in Florida in 1989, and it is expanding its geographical range to threaten Opuntia cactus (Cactaceae) in the southwestern United States, into Mexico, where it is an important economic crop. Laboratory life history studies were conducted at 18, 22, 26, 30, and 34°C to understand cactus moth biology and to develop strategies for control. Duration of immature stages was generally longest at 18°C, declining significantly at 22°C, and shortest at 26, 30, and 34°C. Total immature developmental time from eggs to pupae was ≈180 d at 18°C, 116 at 22°C, and ranged from 65 to 72 d at 26–34°C. Developmental rate for egg-to-pupal stages was estimated using the logistic equation, rate = 0.0165/(1 + (T/20.7093)−5.8823). Percentage survival of immatures was usually lowest at the temperature extremes tested (18 and 34°C), but they did not differ between the sexes. Estimated lower developmental threshold temperature was 13.3°C, resulting in estimated degree-days for development from ≈845 at 18°C to 1,387 at 34°C. In general, pupal weights declined with increasing temperature, and they were always lower in males than in females. Female adult survivorship was longest at 18°C, and shortest at 34°C, with the other treatments clustered between the temperature extremes. The highest reproductive values were found at 30°C, which indicates an approximate optimal temperature. Net reproductive rate (R0), gross reproductive rate (GRR), generation time (T), intrinsic rate of increase (r), finite rate of increase (&lgr;), and doubling time (DT) were 43.68 ♀/♀, 44.02 ♀/♀, 67.14 d, 0.0562 ♀/♀/d, 1.058 ♀/♀/d, and 12.33 d, respectively. An oviposition rate surface describing mean oviposition rate as a function of time and temperature was, eggs = (−11.241 + 0.854T) d exp (−0.020Td). Given the life history characteristics found in this study and other studies, cost-effective pest management strategies against C. cactorum are discussed.

Comparison of functional response and mutual interference between two aphelinid parasitoids of Bemisia argentifolii (Homoptera: Aleyrodidae)

Functional responses and mutual interference were compared in an indigenous parasitoid, Encarsia pergandiella Howard (Hymenoptera: Aphelinidae), with that of an exotic parasitoid, Eretmocerus mundus Mercet (Aphelinidae) from Spain, attacking the silverleaf whitefly, Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae). Type II functional response curves were fitted to the data and were used to calculate handling time. Eretmocerus mundus attacked more whitefly nymphs than E. pergandiella. Handling times estimated from the functional responses were 72 min for E. pergandiella and 12 min for E. mundus, suggesting that lower attack rates for the former parasitoid may be attributed to longer handling times. The statistically estimated handling time for E. mundus was compared with an estimate derived from empirical observations of parasitoid behavior. Actual observations of handling time, defined as oviposition, host feeding and associated preening, yielded a mean handling time of <2 min, suggesting...

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

Abstract Delphastus catalinae (Horn) (Coleoptera: Coccinellidae) is a predator of whiteflies. It is tropical in origin. Whiteflies 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 26°C; hence, vapor pressure deficits ranged from 5.04 to 30.25 mb. The study was conducted using the B-biotype sweetpotato whitefly, 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 ≈90% of the beginning cohort survived to the adult stage. Conversely, ≈85% hatched and ≈60% 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 significantly 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.

Life table analysis for immatures and female adults of the predatory beetle, Delphastus catalinae, feeding on whiteflies under three constant temperatures

Abstract Immature development and reproductive life history of Delphastus catalinae (Horn) (Coleoptera: Coccinellidae) feeding on Bemisia tabaci biotype B (Gennadius) (Homoptera: Aleyrodidae) (= B. argentifolii Bellows and Perring) immatures was studied at three constant temperatures: 22, 26 and 30 °C. Lower developmental threshold temperatures (T0) were estimated at 9 and 9.9 °C, for males and females, respectively. Female adults weighed slightly more than males (0.587 and 0.505 mg, respectively). As temperature increased from 22 to 30 °C, developmental time from eggs to eclosion of the adult declined from 24 to 15 days. Thermal units required for immature development was ∼300 degree-days. Percentage egg hatch declined at increasing temperatures, but no significant effect of time was found. The intrinsic rate of increase, r, increased from 0.048 to 0.082 and doubling time decreased from 14.44 to 8.45 days as temperature increased from 22 to 26 °C. Mean daily fecundity was modeled as a function of time and temperature to create a 3-dimensional surface. Overall, Delphastus catalinae was found to perform better at 22 and 26 °C while 30 °C was detrimental to immature development and adult reproduction.

Foraging Behavior of Field Populations of Diadegma Spp. (Hymenoptera: lchneumonidae):Testing for Density-Dependence at Two Spatial Scales

The foraging behavior of populations of Diadegma spp. (Hymenoptera: Ichneumonidae) attacking the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), was studied in the field. The e...

Evaluation of Steinernema riobravis (Nematoda: Steinernematidae) against the Mexican rice borer (Lepidoptera: Pyralidae).

The virulency of an endemic nematode, Steinernema riobravis Cabanillas, Poinar and Raulston (Nematoda: Steinernematidae), was tested against the Mexican rice borer, Eoreuma loftini(Dyar) (Lepidopte...

Phenology and egg production of the cactus moth (Lepidoptera: Pyralidae): comparison of field census data and life stage development in the field.

Natural phenology and development of the cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), was studied under field conditions in St. Marks National Wildlife Refuge, St. Marks, FL, from July 2006 to September 2007. Pads of cactus (Opuntia stricta Haw. (Cactaceae)) were visually surveyed weekly for presence of moth immature stages. Adult male C. cactorum, populations were surveyed using a pheromone lure and wing style sticky traps. The field census data identified 3 generations per year which generally occurred in August to September, October to April, and May to July. Numbers of eggsticks peaked in midAugust, midOctober and micApril. High numbers of early larval immatures (1st to 3rd instars) were recorded in October 2006, May 2007 and September 2007. High numbers of late-stage larvae (4th to 5th in-star) were recorded in September to October 2006, December to January 2006, June to July 2007. Peak numbers of Cactoblastis male adults occurred approximately in midOctober 2006, April to May 2007, and July to August 2007. Pupae were cryptic and difficult to sample. Development in field cages was studied by introducing cohorts of moth eggs on potted cactus plants (Opuntia ficus-indica (L.) Mill.) into the field at approximately the same times they were found to occur naturally. During the course of each generation, the potted plants were returned to the laboratory for determination of moth lifestage. Body weights and lengths also were recorded. In the field cages, 3 generations were observed and these coincided with the populations that were observed in the open field. However, the generations were more clearly defined because eggs were introduced as cohorts and most insects were recovered. Measurements of larval head capsules and body lengths show that development in the winter generation is slower than that of the summer and fall generations, although peak measurements are approximately identical in all 3 generations. Female pupae weighed 225.25 ([plus or minus] 4.8 SE) mg which was significantly heavier than males weighing 138.01 ([plus or minus] 5.5) mg. Pupal weights differed according to generation, but there was no effect on adult weight. Female adults weighed 130.3 ([plus or minus] 11.3) mg, compared with males, which weighed 60.81 ([plus or minus] 2.4) mg. Adult sex ratio was approximately 1:1. Male adults appeared to have emerged earlier than females in the fall generation.

Life Table Analysis and Development of Singhiella simplex (Hemiptera: Aleyrodidae) under Different Constant Temperatures

ABSTRACT Singhiella simplex (Singh) (Hemiptera: Aleyrodidae) is a newly invasive pest of several species of Ficus plants in the United States. Very little is known about its biology and life history. Here, we studied its development and reproduction at 15, 20, 25, 27, 30, and 35°C. No immatures survived the 35°C treatment. Stage-specific duration times are presented for the other temperatures. Total duration of immature stages varied from 97.1 d at 15°C to 25.2 d at 30°C. Linear functions were used to describe development rates for eggs, instars and pupal stages. Total immature development also was modeled using a nonlinear Briere-1 function: r(T) = aT(T -T0) where r(T) is developmental rate at temperature (T), a = 0.0000146, T0 = 7.3120084 and TL = 45.9512202 (constant, lower developmental threshold, and lethal temperature, respectively). The thermal requirement for development from eggs to pupae was estimated to be 487.8 degree-days. S. simplex reproduction was highest at 27°C, where R0, GRR, T, r, &lgr;, and DT were 23.114 ♀ / ♀, 24.25 ♀/♀, 31.413 d, 0.099 ♀ / ♀ /d, 1.105 ♀ / ♀ /d, and 6.93 d, respectively. The combined effect of temperature and female adult age on daily oviposition rate was modeled using the Enkegaard equation: eggmean = (p + qT) d exp(-wTd), where T is temperature. Parameter estimates were p = -30.21, q = 2.62, and w = 0.034. Duration of female adulthood was 8 d at 15°C, significantly longer than 2.5–4.2 d at the higher temperatures. At 25 and 27°C, lifetime fecundity per female averaged 37.9 and 46.2, respectively.

Reproduction, Longevity, and Survival of Cactoblastis cactorum (Lepidoptera: Pyralidae)

ABSTRACT Screened potted cactus, Opuntia ficus-indica (L.) Mill., plants containing pairs of adult male and female cactus moths, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), were placed in a cactus field in St. Marks, FL, to measure oviposition patterns under ambient conditions. Results showed a narrow window for oviposition during third and sixth day of adult females life. Peak oviposition activity occurred on the third day, whether measured in total fecundity, numbers of eggs per egg stick or numbers of ovipositions. After the third day, not only did oviposition rate decrease but also the quality of eggs produced declined. Percentage of egg hatch decreased and egg incubation increased. Longevity of adult males (6.3 ± 0.79 d) did not differ from that of females (5.2 ± 0.4), although female adults (157.8 ± 4.5 mg) weighed more than males (74.9 ± 1.51). Therefore, from the perspective of mass rearing this moth, the optimal time for collecting eggs is limited to the third day in the life of the adult female.