Insecticidal Control of Adult Haptoncus luteolus as a Component of a Comprehensive Sap Beetle Management Plan in Strawberries

Abstract

Field and laboratory experiments were conducted to determine the usefulness of aqueous sprays of Assail® (acetamiprid), Brigade® (bifenthrin), DPX-HGW86 (cyantraniliprole), Coragen® (Rynaxypyr®), and Rimon® (novaluron), candidate insecticides for adult sap beetle control. Assail® and Brigade® were shown to be effective control agents for adult Haptoncus luteolus and Assail® likely possesses an advantage over Brigade® when H. luteolus enter fields and quickly abandons insecticide-treated surfaces to enter strawberry fruit. Assail® and Brigade® adulticides can be important components of comprehensive programs of sap beetle management that include removal of all ripe fruit from the strawberry field and use of Rimon® insect growth regulator larvacide.

Keywords:

• Nitidulidae
• Haptoncus luteolus
• chemical control
• adult control
• acetamiprid
• bifenthrin
• cyantraniliprole
• novaluron
• Rynaxypyr®

INTRODUCTION

Strawberries, mostly for the fresh market, were produced on 3,601 ha in Florida (National Agric. Statistics Service, 2010a) and valued at about $362 million during 2010 (National Agric. Statistics Service, 2010b). There are numerous arthropod pests that affect these Florida strawberries, principally spider mites, thrips, sap beetles, aphids, and some moth larvae. Adequate remedies exist for most, but excellent control measures are lacking to manage sap beetles through the production season.

Sap beetles normally enter the strawberry fruiting fields from nearby trees and surrounding fields as weather warms in February. They are attracted to fruit damaged by rain, overhead watering for frost protection, botrytis fruit rot disease, other diseases, insect feeding, etc. Lannate® (methomyl) once was useful to manage the problem, but this insecticide no longer is available to the United States strawberry industry. As a result, growers have relied on removal of all ripe fruit, salable or unsalable, and poorly understood insecticides for management. These practices often still leave unacceptable numbers of sap beetles in the field.

Rimon® (novaluron) is a benzoylurea inhibitor of chitin biosynthesis type O insecticide (an insect growth regulator) and has been shown to be very effective to reduce presence of sap beetle larvae generated from adults that enter strawberry fields (Price and Nagle, 2010). Companion insecticides for adult control are needed adjunct to sanitation and larval control.

Experiments were conducted to elucidate the insecticides most likely to control adult Haptoncus luteolus sap beetles, the most commonly encountered sap beetle adult in strawberries of the Plant City Florida production area (Potter, 1995).

MATERIALS AND METHODS

Experiments 1 and 2 (Field)

Similar experiments were performed in 2009 and 2010 to evaluate the usefulness of candidate insecticides for management of sap beetles in strawberries at the University of Florida Gulf Coast Research and Education Center (UF GCREC), Wimauma, FL. Transplants were set on 13 Oct. 2008 (expt. 1) and 12 Oct. 2009 (expt. 2) in plastic mulched beds, spaced at 1.22 m, 0.33 m high, and 0.69 m wide. Overhead irrigation was applied for the first 2 weeks to aid in establishment. Drip irrigation was used for the remainder of the experiment. Plots of ‘Treasure’ were not harvested after late January to enhance sap beetle presence. Each plot consisted of 20 plants in two 10-plant rows per bed. Treatments and a non-treated check (Tables 1 and 2) were replicated four times in a randomized complete block design. Treatments were applied using a hand-held sprayer with a spray wand outfitted with a nozzle containing a 45-degree core and a no. 4 disc. The sprayer was powered by CO₂ pressurized to 2.8 kg/cm² and calibrated to deliver 935 L/ha. All treatments initially were applied on 18 Feb. 2009 (expt. 1) or 3 Mar. 2010 (expt. 2) and were reapplied at 1, 2, or 3 week intervals (expt. 1) or 1 or 2 week intervals 2010 (expt. 2) (Tables 1 and 2). Pre-treatment samples were taken 2 days before initial applications of treatments by inspecting the plants and surrounding plastic for 5 min then reporting observations to a recording assistant. Data were recorded as adult H. luteolus observed within a 5 min session per plot. Data were transformed using √(x + 0.5) prior to ANOVA and means were separated by Fisher's Protected LSD (P ≤ 0.05). Non-transformed means are reported.

TABLE 1 Schedule of Treatment Applications (expt. 1, 2009, UF GCREC Field)

		Date of treatment application
Treatment ^z	Amount per ha	18 Feb.	24 Feb.	4 Mar.	11 Mar.	19 Mar.	31 Mar.
Non-treated	—
Brigade 10% WSB	1,679 g	X	X	X
Brigade 10% WSB	1,679 g	X		X		X
Brigade 10% WSB	1,679 g	X			X		X
Rimon 0.83EC	877 mL	X	X	X
Rimon 0.83EC	877 mL	X		X		X
Rimon 0.83EC	877 mL	X			X		X
Rimon 0.83EC	657 mL	X		X		X
Rimon 0.83EC +	657 mL	X		X		X
Brigade 10% WSB	1,679 g
Rimon 0.83EC +	877 mL	X	X	X
Brigade 10% WSB	1,679 g
Rimon 0.83EC +	877 mL	X		X		X
Brigade 10% WSB	1,679 g
Rimon 0.83EC +	877 mL	X			X		X
Brigade 10% WSB	1,679 g
Rimon 0.83EC +	877 mL	X		X
Assail 30SG	484 g
Assail 30SG fb	484 g	X				X
Rimon 0.83EC	877 mL			X			X
Assail 30SG fb	484 g	X		X
Rimon 0.83EC	877 mL		X		X
^zA ‘+’ sign indicates the products were combined, ‘fb’ indicates followed by.

TABLE 2 Schedule of Treatment Applications (expt. 2, 2010, UF GCREC Field)

		Date of treatment application
Treatment ^z	Amount per ha	3 Mar.	11 Mar.	18 Mar.	24 Mar.	31 Mar.	7 Apr.
Non-treated	—
Brigade 10% WSB	1,679 g	X		X		X
Brigade 10% WSB +	1,679 g	X		X		X
Rimon 0.83EC	438 mL
Rimon 0.83EC	438 mL	X	X	X	X	X	X
Rimon 0.83EC	877 mL	X		X		X
^zA ‘+’ sign indicates the products were combined.

Experiments 3, 4, and 5 (Laboratory)

The effects of dried insecticide residues on adult H. luteolus sap beetles were evaluated by comparison to a non-treated control in a laboratory study at UF GCREC (Table 3). Three experiments were performed, each replicated in time four times between Jan. and Apr. 2010. Each experiment involved a different period of potential sap beetle adult exposure to the treated substrate, either 2, 5, or 24 hr, by Assail® (acetamiprid), Brigade® (bifenthrin), Coragen® (Rynaxypyr®), DPX-HGW86 (cyantraniliprole), or a non-treated check.

TABLE 3 Effects of Insecticides on Haptoncus luteolus Adults after 2, 5, or 24 hr of Exposure (expt. 3–5, 2010, UF GCREC Laboratory)

		Active adults observed 48 hr after the indicated exposure period (% of total)
Treatment ^z	Amount per L	2 hr	5 hr	24 hr
Non-treated	—	87.67a	94.54a	85.71a
Assail 30SG	0.52 g	4.38c	11.50b	2.08c
Brigade WSB	1.80 g	32.84b	10.16b	2.08c
Coragen 1.66 SC	0.37 mL	81.87a	85.68a	78.91a
DPX-HGW86 10SE	1.61 mL	79.31a	78.06a	44.95b
^zData were transformed arcsine[√(x + 0.5)] prior to ANOVA; non-transformed means are reported. Mean separation within columns by Fisher's Protected LSD (P ≤ 0.05).

Groups of 10 to 12 H. luteolus adults were aspirated from a laboratory colony and held in vials for 1 to 2 hr during which the treatments were applied in a greenhouse as follows. Each chemical preparation was sprayed as a fine mist, using a CROWN® Spra-Tool® disposable spray gun (Aervoe Industries Inc., Gardnerville, NV), onto 12-cm diameter discs of agricultural plastic mulch substrates and allowed to air dry for about 1 hr. The plastic mulch substrates then were transported to the laboratory where each was placed treated side up, above the overturned lid of a 100 × 15 mm polystyrene Petri dish.

A 13-mm diameter × 6-mm disk of apple was placed in the center of each disc of treated substrate to provide food and moisture for the sap beetles. Sap beetles from one vial were deposited near the center of each substrate, and then the overturned bottom of the Petri dish was placed into and attached to the overturned lid by cellophane tape. Sap beetles were exposed to the treated substrate and apple piece for the prescribed period.

Immediately after exposure, the sap beetles and the apple disk were transferred to a zip closure plastic bag to remain in the laboratory until observations of exposure effects concluded 48 hr later. The condition of each sap beetle was determined with the aid of a dissecting microscope and recorded as either “active” (likely able to damage fruit), “moribund” (having impaired movement and unlikely able to damage fruit), or “dead.” The percent of sap beetles fitting each category was calculated, transformed using arcsine [√(%x/100)] prior to ANOVA, and means were separated by Fisher's Protected LSD (P ≤ 0.05) test. Only data of active beetles are reported. Data are reported as non-transformed means.

RESULTS AND DISCUSSION

Experiments 1 and 2 (Field)

The lowest average numbers of H. luteolus observed per 5 min through the season in expt. 1 (2009) occurred when Brigade® (0.00–0.07) or Assail® (0.00–0.18) were included in the program of application (Table 4). The highest average number of H. luteolus observed per 5 min through the season occurred in the untreated check (0.57). There were no significant differences between average seasonal occurrence under programs that included Assail® or Brigade®.

TABLE 4 Response of Adult Haptoncus luteolus to Treatments (expt. 1, 2009, UF GCREC Field)

Treatment ^z, ^y	Amount per ha	Application interval	Average no./5 min observation ^v
Non-treated	—	—	0.57a
Brigade 10% WSB	1,679 g	1-week	0.00e
Brigade 10% WSB	1,679 g	2-week	0.04e
Brigade 10% WSB	1,679 g	3-week	0.06e
Rimon 0.83EC	877 mL	1-week	0.29bcd
Rimon 0.83EC	877 mL	2-week	0.57a
Rimon 0.83EC	877 mL	3-week	0.39abc
Rimon 0.83EC	657 mL	2-week	0.46ab
Rimon 0.83EC +
Brigade 10% WSB	657 mL + 1679 g	2-week	0.00e
Rimon 0.83EC +
Brigade 10% WSB	877 mL + 1679 g	1-week	0.04e
Rimon 0.83EC +
Brigade 10% WSB	877 mL + 1679 g	2-week	0.00e
Rimon 0.83EC +
Brigade 10% WSB	877 mL + 1679 g	3-week	0.07de
Rimon 0.83EC +
Assail 30SG ^x	877 mL + 484 g	2-week	0.00e
Assail 30SG fb	484 g fb
Rimon 0.83EC ^w	877 mL	2-week	0.14de
Assail 30SG fb
Rimon 0.83EC ^w	484 g + 877 mL	1-week	0.18cde
^zAll treatments were applied three times except where noted; a ‘+’ sign indicates the products were combined, ‘fb’ indicates followed by.
^yData were transformed √(x + 0.5) prior to ANOVA; non-transformed means are reported. Mean separation within columns by Fisher's Protected LSD (P ≤ 0.05).
^xThis tank mix was applied twice at the indicated interval.
^wThis alternation was repeated resulting in a total of four applications at the indicated interval.
^vData are the average of seven post-treatment samples taken between 23 Feb. and 6 Apr.

The fewest seasonal average numbers of adult H. luteolus observed in 5 min during expt. 2 (2010) occurred each time Brigade® was included in the treatment (0.25) or Rimon® was applied at the highest concentration (0.68) (Table 5). There was, however, no significant difference between average seasonal numbers of adult H. luteolus observed in 5 min from the Rimon® treatment (0.68) and the numbers observed in the non-treated check (1.11) (Table 5).

TABLE 5 Response of Adult Haptoncus luteolus to Treatments (expt. 2, 2010, UF GCREC Field)

Treatment ^z, ^y	Amount per ha	Application interval	Average no./5 min observation ^w
Non-treated	—	—	1.11a
Brigade 10% WSB	1,679 g	2-week	0.25b
Brigade 10% WSB +	1,679 g
Rimon 0.83EC	438 mL	2-week	0.25b
Rimon 0.83EC ^x	438 mL	1-week	0.75a
Rimon 0.83EC	877 mL	2-week	0.68ab
^zAll treatments were applied three times at 2-week intervals except where noted; a ‘+’ sign indicates the products were combined.
^yData were transformed √(x + 0.5) prior to ANOVA; non-transformed means are reported. Mean separation within columns by Fisher's Protected LSD (P ≤ 0.05).
^xThis treatment was applied six times at 1-week intervals.
^wData are the average of seven post-treatment samples taken between 9 Mar. and 20 Apr.

Experiments 3, 4, and 5 (Laboratory)

Forty-eight hours after 2 hr of exposure (expt. 3) the fewest active beetles (4.38%) were found in arenas with mulch substrate treated with Assail® (Table 3). There was also a significant reduction in active beetles in arenas with mulch substrate treated with Brigade® (32.84%) compared to the non-treated check (87.67%) (Table 3).

Forty-eight hours after 5 hr of exposure (expt. 4) the fewest active beetles were observed in arenas with mulch substrate treated with either Assail® (11.50%) or Brigade (10.16%) (Table 3).

Forty-eight hours after 24 hr of exposure (expt. 5) the fewest active beetles were observed in arenas with mulch substrate treated with either Assail® (2.08%) or Brigade® (2.08%) (Table 3). There was also a significant reduction in active beetles in arenas with mulch substrate treated with DPX-HGW 86 (44.95%) compared to the non-treated check (85.71%) (Table 3).

These data indicate that there is no benefit for control of H. luteolus adults derived from dried residues of Coragen® and only a slight benefit of DPX-HGW86 and then only after 24 hr of exposure. Exposure of H. luteolus adults to dried Assail® residues appears to disable the insects rapidly, while exposure to dried residues of Brigade® disables the insects only after longer exposures. Assail® likely has an advantage over Brigade® when adult H. luteolus insects enter a strawberry field and quickly abandon treated surfaces to chew into strawberry fruit. Assail® and Brigade® are of different modes of action (IRAC, 2012) and possess modes of action different from Rimon® larvacide. As such, they could be part of an insecticide rotation plan to minimize acquisition of resistance to insecticides among H. luteolus. Both Assail® and Brigade® adulticides can contribute to a comprehensive program of sap beetle control that includes the removal of all ripe fruit from the field and use of Rimon® larvacide.

ACKNOWLEDGMENT

The authors are grateful for the funding for this work provided by the Florida Strawberry Growers Association.