Stephen L. Lapointe

Effect of soil moisture on development of Diaprepes abbreviatus (Coleoptera: Curculionidae)

We conducted trials to determine conditions of soil moisture required to optimize production of adults of Diaprepes abbreviatus (L.) in a laboratory colony. Larvae of D. abbreviatus were reared on a commercially available artificial diet and then placed in soil with water content ranging from 20 to 80%. Optimal moisture content of soil for pupation was determined to be 60 10% by weight. When 68-d-old larvae were transferred from artificial diet to soil with these moisture levels and constant temperature (25C), mean ( SEM) development time of D. abbreviatus from neonate to pupa was 126 2.3 d (n = 47). For all pupae, the time required for pupation did not vary with soil moisture. When 68-d-old larvae were taken from diet and placed in soil, the proportion that pupated varied with moisture content. Low (20-40%) and high (80%) moisture content resulted in increased mortality, and fewest larvae pupated within the low range. The mean SEM number of days to pupation of 68-d-old larvae was 58.2 2.3 (n = 47). Older (180 d) larvae reared on diet pupated over a greater range of moisture treatments (30-70%) and were adversely affected only by the highest (80%) and lowest (20%) treatments. Mean SEM time to pupation (38.4 1.9 d, n = 54) did not vary for 180-d-old larvae kept at 30-70% moisture content.

Phylogenetic and Structural Relationships of the PR5 Gene Family Reveal an Ancient Multigene Family Conserved in Plants and Select Animal Taxa

Pathogenesis-related group 5 (PR5) plant proteins include thaumatin, osmotin, and related proteins, many of which have antimicrobial activity. The recent discovery of PR5-like (PR5-L) sequences in nematodes and insects raises questions about their evolutionary relationships. Using complete plant genome data and discovery of multiple insect PR5-L sequences, phylogenetic comparisons among plants and animals were performed. All PR5/PR5-L protein sequences were mined from genome data of a member of each of two main angiosperm groups—the eudicots (Arabidoposis thaliana) and the monocots (Oryza sativa)—and from the Caenorhabditis nematode (C. elegans and C. briggsase). Insect PR5-L sequences were mined from EST databases and GenBank submissions from four insect orders: Coleoptera (Diaprepes abbreviatus and Biphyllus lunatus), Orthoptera (Schistocerca gregaria), Hymenoptera (Lysiphlebus testaceipes), and Hemiptera (Toxoptera citricida). Parsimony and Bayesian phylogenetic analyses showed that the PR5 family is paraphyletic in plants, likely arising from 10 genes in a common ancestor to monocots and eudicots. After evolutionary divergence of monocots and eudicots, PR5 genes increased asymmetrically among the 10 clades. Insects and nematodes contain multiple sequences (seven PR5-Ls in nematodes and at least three in some insects) all related to the same plant clade, with nematode and insect sequences separating as two clades. Protein structural homology modeling showed strong similarity among animal and plant PR5/PR5-Ls, with divergence only in surface-exposed loops. Sequence and structural conservation among PR5/PR5-Ls suggests an important and conserved role throughout the evolutionary divergence of the diverse organisms from which they reside.

Effects of a Particle Film on Biology and Behavior of Diaphorina citri (Hemiptera: Psyllidae) and Its Infestations in Citrus

Abstract Studies were conducted to investigate the effects of a kaolin-based hydrophilic particle film, Surround WP, on the biology and behavior of the psyllidDiaphorina citri Kuwayama (Hemiptera: Psyllidae) and to assess population densities ofD.citri in citrus subjected to monthly applications of Surround WP. Laboratory investigations indicated a 3% (wt:vol) suspension of Surround WP in water applied directly was not acutely toxic to eggs, older nymphs or adults. Presence of the dried particle film on leaves interfered with the ability of adults to grasp and walk on citrus leaves. During a 30-s period, adults spent an average of 5 s moving on leaves with particle film compared with 16 s on leaves without particle film. When leaves were inverted, a significantly higher percentage of adults fell or flew from treated leaves (53%) than untreated leaves (16%). In a 12-mo study investigating infestations ofD.citri on citrus treated monthly with Surround WP, cumulative reductions of 78% in adult numbers on mature leaves and of 60% in adult numbers on flush shoots (immature leaves) were observed in treated trees compared with untreated trees. Numbers of eggs and nymphs per flush shoot were reduced by 85 and 78%, respectively, in trees treated with particle film. Reductions in infestation levels ofD.citri in treated trees were attributed to the negative effects of the particle film on the ability of adults to grasp, move, and oviposit. The suppressive effects of a Surround treatment against adult psyllids were degraded by rain.

Particle Film Deters Oviposition by Diaprepes abbreviatus (Coleoptera: Curculionidae)

Abstract A hydrophilic formulation of the inert silicate kaolin was tested in a screenhouse for its effect on the behavior of the root weevil Diaprepes abbreviatus (L.), a pest of citrus and ornamental plants in Florida and the Caribbean. Feeding by adults on treated foliage was reduced by 68–84% compared with adults fed untreated foliage. No insecticidal activity was detected after 14 d of exposure to kaolin-treated leaves. Oviposition was completely suppressed on treated foliage. Although females oviposited >19,000 eggs during two trials on untreated foliage, no egg masses were found on foliage treated with the kaolin formulation. These data indicate potential for kaolin as a barrier to oviposition in citrus groves and may prove to be an economically viable and environmentally sound component of an integrated approach for control of D. abbreviatus and related root weevils.

EVALUATION OF HOST PLANTS AND A MERIDIC DIET FOR REARING MACONELLICOCCUS HIRSUTUS (HEMIPTERA: PSEUDOCOCCIDAE) AND ITS PARASITOID ANAGYRUS KAMALI (HYMENOPTERA: ENCYRTIDAE)

Abstract Biological control programs of Maconellicoccus hirsutus (Green), in the Caribbean have relied on Japanese pumpkins and sprouted potatoes as hosts for rearing both the mealybug and its parasitoids. However, seasonal shortages of these substrates have necessitated that others be found with equal or better qualities for sustaining large mealybug populations. In this paper, we report experiments comparing mass-rearing M. hirsutus on acorn squash (Cucurbita pepo L. var. ‘Turbinata’), chayote (Sechium edule [Jacques]), and prickly pear, Opuntia ficus-indica [L.]) with Japanese pumpkin and sprouted potato. In addition, a simple meridic diet based on canned pumpkins was developed and compared. Acorn squash produced large quantities of females (up to 1,300 per squash) with a life cycle and reproductive potential equal to that of mealybugs reared on Japanese pumpkin. Parasitoids reared on these mealybugs developed normally and had a female-biased sex ratio similar to those reared on mealybugs on Japanese pumpkins or potato sprouts. Development of M. hirsutus reared on chayote and prickly pear was delayed by 1.5-5.0 days compared to that of mealybugs reared on Japanese pumpkins. Mealybugs on these substrates produced parasitoids with prolonged developmental times and male-biased sex ratios. On diet, development and reproduction of M. hirsutus was possible only for 3 to 4 consecutive generations. Mealybugs with longer developmental time, lower survival, and smaller ovisacs with lower percentage eclosion were obtained. Parasitoids reared from these mealybugs did not possess desirable characteristics for biological control. The developmental rate of adult parasitoids increased linearly with that of female hosts depending on the quality of the rearing substrate for the mealybugs.

Effect of Low Temperatures on Mortality and Oviposition in Conjunction With Climate Mapping to Predict Spread of the Root Weevil Diaprepes abbreviatus and Introduced Natural Enemies

Abstract The tropical root weevil, Diaprepes abbreviatus (L.), has been a pest of citrus and ornamental plants since its introduction into Lake County, FL, in 1964. Since then, it has colonized the Florida peninsula to the south of its point of introduction but has not expanded its range to the north. A lower threshold for oviposition by D. abbreviatus was estimated as 14.9°C. Eggs were highly susceptible to cold, with 95% mortality (LTime95) occurring in 4.2 d at 12°C. Relative susceptibility of life stages to cold was eggs > pupae > larvae > adults. Archived weather data from Florida were examined to guide a mapping exercise using the lower developmental threshold for larvae (12°C) and the lower threshold for oviposition (15°C) as critical temperatures for mapping the distribution of D. abbreviatus and the potential for establishment of egg parasitoids. Probability maps using the last 10 yr of weather data examined the frequency of at least 10, 15, 20, 25, or 30 d per winter when soil temperature was ≤12°C. The geographic area that experienced between 15 and 20 d per winter with mean daily soil temperature ≤12°C closely approximated the northern limit of D. abbreviatus in Florida. Homologous maps of Arizona, California, and Texas predict the areas where soil temperatures favor establishment of D. abbreviatus. Successful establishment of egg parasitoids in Florida seems to be limited to southern Florida, where mean daily air temperatures fall below 15°C <25 d/yr. By this measure, we predict that egg parasitoids will not establish in Arizona, California, or Texas.

Thermal Requirements for Development of Diaprepes abbreviatus (Coleoptera: Curculionidae)

Abstract The root weevil Diaprepes abbreviatus (L.) was reared on artificial diet under controlled conditions of temperature and humidity. The lower thermal threshold for development of neonate larvae was estimated to be 15°C. The growth rate of neonate larvae increased exponentially with increasing temperature up to 30°C. The growth rate of later instars, however, was suppressed at 30°C and mortality was higher than that of larvae reared at 26°C. Larvae reared as late instars only (>56 d old), or continuously at 30°C, had increased mortality and produced smaller adults than larvae reared at 22 and 26°C. Larvae reared as late instars only (>56 d) or continuously at 22°C had similar survival rates compared with those reared at 26°C, and they emerged as larger adults compared with larvae reared at 26 or 30°C. The time required for development from neonate to pupation was 125 ± 3 d (mean ± SEM, n = 38) at 26°C. Duration of the pupal stage was inversely proportional to temperature between 22 and 30°C. Pupal mortality was higher at 30°C than at 22 or 26°C. The total time required for a single generation from oviposition to adult emergence was estimated to be 154 d at 26°C and adequate humidity. Cumulative mean air and soil temperatures and rainfall for a location in central Florida were analyzed and presented for the period October 1991 through January 1999.

Insect diets as mixtures: Optimization for a polyphagous weevil

Development or improvement of artificial insect diets can be tedious, convoluted and often under-appreciated. Using n-dimensional mixture designs, we identified a set of response-optimized meridic diets that contain fewer ingredients than the current commercial diet for Diaprepes abbreviatus, a polyphagous weevil pest of the Caribbean and southern U.S. A diet blend optimized to produce maximum adult weight was predicted to produce adult D. abbreviatus that weigh 28% more compared with adults reared on the standard commercial diet. Diet blends that produced greater individual adult weights resulted in lower survival compared with those blends that yielded adults of more modest proportions. In contrast, a simplified high cottonseed meal blend produced smaller adults more similar to field-collected individuals, and produced the greatest number of adults and the greatest biomass at relatively low cost compared with diets that yielded adult weevils of greater weight. We think that many insect-rearing programs would benefit from application of mixture design methods to situations where diet optimization is desired for researcher-selected criteria. This approach is broadly applicable to any problem that can be conceptualized as a mixture problem.

Reduced oviposition by Diaprepes abbreviatus (Coleoptera: Curculionidae) and growth enhancement of citrus by Surround particle film.

Abstract Regularly applied sprays of a particle film, Surround WP, greatly enhanced the growth of citrus trees on a poorly drained Winder soil at Fort Pierce, FL. After 3 yr of applications every 3 or 4 wk, Surround-treated trees had at least 5 times the mass, 6 times the canopy volume, and ≈4 times the cross-sectional area of the tree stems at the graft union compared with untreated trees. The larger Surround-treated trees attracted a higher number of adult weevil Diaprepes abbreviatus (L.) and to a lesser extent citrus root weevil, Pachnaeus litus (Germar), per tree, but there was an equivalent number of egg masses per tree compared with the control trees. The number of egg masses per female weevil oviposited on Surround-treated trees was significantly less than either the control trees or trees treated biannually with an entomopathogenic nematode, BioVector. The number of larvae per tree recovered from the roots of excavated trees was greater from trees treated with Surround once every 3 wk compared with control trees. The data suggest that Surround particle film greatly enhanced the growth of citrus trees grown in a poorly drained soil. The reduction in oviposition by D. abbreviatus was insufficient to significantly reduce the number of root weevil larvae per tree feeding on the roots. However, the more vigorous trees resulting from Surround applications may be more resistant or tolerant to root weevil feeding.

FIELD EVALUATION OF A SYNTHETIC FEMALE SEX PHEROMONE FOR THE LEAFMINING MOTH PHYLLOCNISTIS CITRELLA (LEPIDOPTERA: GRACILLARIIDAE) IN FLORIDA CITRUS

Traps baited with a binary mixture in the ratio of 30:10 of two EAG-active compounds, (Z,Z,E)-7,11,13-hexadecatrienal and (Z,Z)-7,11-hexadecadienal, attracted significantly more moths of the leafmining moth, Phyllocnistis citrella, compared with unbaited traps in a Florida citrus grove. The addition of a third EAG-active compound (Z)-7-hexadecenal, did not increase trap catch. Trap height, at 0.7, 1.3 and 2 m, did not significantly affect daily trap catch on 5 of 6 days. Mention of a trade mark or proprietary product does not constitute a guarantee or warranty of the product by the US Department of Agriculture and does not imply its approval to the exclusion of other products that also may be suitable.